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Abstract: This paper presents the effect of silane treatment of S-2 Glass fibres on the fracture toughness and water sorption/solubility behaviour of fibre-reinforced flowable dental composites. The effect of epoxy- and methacrylate-based silane coupling agents (SCAs) on the mechanical strength and hydrolytic properties were investigated. The concentration of the selected SCAs on the mechanical and physical properties were investigated. The influence of molecular structure and concentration in the interfacial adhesion at the fibre-matrix interfaces was also studied. Short S-2 Glass fibres of 250 µm in length and 5 µm in diameter were etched with acid to remove any impurities and roughen the surface. The acid-etched fibres were silane treated with 3MPS, 3GPS, and 8MOTS at different concentrations by weight (%). The silane-treated fibres were incorporated at 5 % into the dental resin mixture. Untreated fibres were added at 5 % to the dental resin mixture and served as the control group. The physical properties such as water sorption, solubility, and desorption along with mechanical properties such as fracture toughness and total fracture work of the fibre-reinforced dental composites grafted with the above-mentioned SCAs were evaluated. The surface morphology of the fractured surface was studied and analysed. The fracture toughness tests showed that the dental composites grafted with optimum weight per cent (wt. %) concentration of the SCA had a better stress intensity factor (KIC) when compared to the 2.0 wt. % and 3.0 wt. % concentration. The KIC value of dental composites grafted with untreated surface etched glass fibres was less than the KIC values of dental composites grafted with optimum concentrations of 3MPS, 3GPS, and 8MOTS by 81.6 %, 38.6 %, and 110.5 %, respectively. A similar trend was found while investigating the total work of fracture of the dental composites, between optimum concentration, 2.0 wt. % and 3.0 wt. % concentration of respective SCA. The increase in silane concentration also led to an increase in the water sorption/solubility characteristics. The absorption of water was most severe in the fibre-reinforced dental composites without silane treatment (32.9 µg/mm3). The ANOVA results showed that the fibre-reinforced dental composites grafted with 8MOTS at optimum concentration showed an increase in fracture toughness when compared to optimum concentrations of 3GPS and 3MPS by 51.9 % and 15.9 %, respectively. The enhanced mechanical and physical characteristics are due to the increased adhesion between the fibre and silane achieved from the optimum wt. % concentration of 8MOTS. Similarly, dental composites grafted with 8MOTS at optimum concentration showed a decrease in water sorption characteristics when compared to optimum concentrations of 3GPS and 3MPS by 18.2 % and 0.6 %, respectively. The decreased water sorption characteristics at the optimum concentration of 8MOTS could be due to the reduced availability of reactive hydroxyl groups and the hydrophobic characteristics of 8MOTS. Silane coupling agents (SCAs) are important components of dental composites. The type and concentration of SCA have a significant effect on material properties. The current study focuses on understanding the effects of different SCAs and wt. % concentrations on the interfacial fracture behaviour and the influence of different SCAs on the water sorption and solubility behaviour of S-2 Glass fibre-reinforced flowable dental composites.

���ܳٳ�ǰ���:��Jerrin Thadathil Varghese, Kiho Cho, Raju, Paul Farrar, Leon Prentice, B. Gangadhara Prusty
Year:��2023
Journal name: Dental Materials

Abstract: Embedded optical fibre sensors (OFSs) offer the potential to monitor the internal strains at various stages during the manufacturing and service life of fibre-reinforced polymer (FRP) composite structures. Various aspects associated with the embedment of OFSs, such as integration, material compatibility, and sensing performance of the embedded sensor needs to be investigated to develop reliable OFSs based internal sensing platform for composite structures. In this study, Polyimide (PI) and Polyether ether ketone (PEEK) coated optical fibres (OF) were embedded into glass fibre-reinforced polymer (GFRP) composites to evaluate four important aspects associated with the embedment of OFs, which include; i). Structural integrity of the OFs against chemical reactions from vinyl ester resin and its additives through immersion testing, ii). Methods of integrating the OFs into layered glass fibres for the vacuum resin infusion manufacturing process, iii). Sensing performance of the embedded OFs during manufacturing and structural testing (tensile and compressive), and iv). Internal structural integrity of the embedded OFs and the host composite structure using X-Ray micro-computerised tomography technique (μ-CT). The results from the immersion testing and manufacturing process monitoring showed that both PEEK and PI coated OFs can resist the chemical and mechanical stresses caused by resin polymerisation during curing process. The subsequent mechanical testing showed a similar sensing performance by the PI and PEEK coated OFs. Under tensile loads, the OFs monitored the tensile strain distribution up to 7,000 με and compressive strain distribution up to −1,200 με under flexural loading without compromising their optical performance. Finally, the μ-CT scanning results had shown a minimal structural deterioration of the embedded OFs and host composite structure. The outcomes from this detailed experimental investigation on the embedment of OFS in GFRP structures provided useful information towards the integration and performance of optical sensors in composite structures.

Authors: Prashanth Nagulapally, Mohammed Shamsuddoha, Thinu Herath, Luke Djukic, Gangadhara Prusty.
Year:��2023
Journal name: Journal of Composite Materials

Abstract: Robotic manufacturing using automated fibre placement (AFP) provides the foundation for efficient, low labour intensive, high accuracy and repeatable composite manufacturing. This paper presents a novel manufacturing process used to build a full-scale shape-adaptive composite hydrofoil using AFP. The outer layers of the hydrofoil were made up of carbon-fibre/epoxy plies laid up by AFP. The inner core of the hydrofoil was made from an E-glass/epoxy laminate, which was used as a rotatable “core-wrap” mandrel to place the carbon plies on. This type of core-wrapping manufacturing process allowed the consolidation of continuous carbon fibres around the leading and trailing edges and minimised the risk of premature delamination failure. Fibre orientations of the AFP-laid carbon plies were optimised using a genetic algorithm for a shape-adaptive response, and the manufacturing process from the layup to the curing is presented. The manufacturing downtime, dimensional variation and AFP-inherent imperfections and underlying reasons for their occurrence were discussed for future improvement. It was found that the manufactured hydrofoil has a lower laminate thickness than the expected profile due to not using female moulds during the cure process. About half of the AFP operation time was spent on several downtimes such as ply inspection and layup rework. Intrinsic tow defects such as tow upfolding and wrinkling mostly occurred around the narrow-curvature trailing edge and contributed largely to layup rework time.

Authors: Phyo Thu Maung, B. Gangadhara Prusty, Ebrahim Oromiehie, Andrew W. Phillips & Nigel A. St John
Year:��2023
Journal name: The International Journal of Advanced Manufacturing Technology

Abstract: This study reports the findings on the impact behaviour of metal-composite structures. Carbon fibre/Epoxy composite laminates were manufactured by using the Automated Fibre Placement (AFP) technique. Subsequently, hybrid structures were fabricated by bonding fibre laminate and aluminium plate together. The hybrids were tested at low velocity impact energies to probe the role of AFP composite laminates on the performance of the hybrid system. Our findings show that the bonding of the composite onto aluminium plate increased the natural frequency (stiffness) of the system and its energy absorption capability by almost 40 %. It was also found that the fibre layout of AFP composite significantly improved the central deflection of the hybrid. For instance, the deflection of cross-ply hybrids was 15% less in comparison to their counterparts with unidirectional fibrous composites. Nevertheless, under the investigated energies, the fibre layout appeared to have a marginal influence on the peak contact force. Post-mortem examination showed that at an impact energy of 150 J there was no fibre failure observed in asymmetric FMLs with unidirectional composite laminates. Conversely, the fibre failure in cross-ply hybrids occurred at 150 J. This suggests that less energy is required to induce fibre failure energy in cross-ply hybrids when compared to their unidirectional hybrid counterparts. Furthermore, it was also found that substrate treatment was successful in preventing excessive delamination, even though its influence on the peak contact force was not significant.

Authors: A. Serubibi, P.J. Hazell, J.P. Escobedo, H. Wang, E. Oromiehie, B.G. Prusty
Year:��2023
Journal name: Materials Today: Proceedings

Abstract: There are several complications associated with lumbar interbody fusion surgery however, pseudarthrosis (non-union) presents a multifaceted challenge in the postoperative management of the patient. Rates of pseudarthrosis range from 3 to 20 % in patients with healthy bone and 20 to 30 % in patients with osteoporosis. The current methods in post-operative follow-up - radiographs and CT, have high false positive rates and poor agreement between them. The aim of this study was to develop and test a proof-of-concept load-sensing interbody cage that may be used to monitor fusion progression. Piezoresistive pressure sensors were calibrated and embedded within a polyether ether ketone (PEEK) interbody cage. Silicone and poly (methyl methacrylate) (PMMA) were inserted in the graft regions to simulate early and solid fusion. The load-sensing cage was subjected to distributed and eccentric compressive loads up to 900 N between synthetic lumbar vertebral bodies. Under maximum load, the anterior sensors recorded a 56–58 % reduction in pressure in the full fusion state compared to early fusion. Lateral regions measured a 36–37 % stress reduction while the central location reduced by 45 %. The two graft states were distinguishable by sensor-recorded pressure at lower loads. The sensors more effectively detected left and right eccentric loads compared to anterior and posterior. Further, the load-sensing cage was able to detect changes in endplate stiffness. The proof-of-concept ‘smart’ cage could detect differences in fusion state, endplate stiffness, and loading conditions in this in vitro experimental setup.

Authors: Vivek A.S. Ramakrishna, Uphar Chamoli, Subhas C. Mukhopadhyay, Ashish D. Diwan, B. Gangadhara Prusty
Year:��2023
Journal name: Journal of Biomechanics

Abstract: Extreme lateral interbody fusion (XLIF) may be performed with a standalone interbody cage, or with the addition of unilateral or bilateral pedicle screws; however, decisions regarding supplemental fixation are predominantly based on clinical indicators. This study examines the impact of posterior supplemental fixation on facet micromotions, cage loads and load-patterns at adjacent levels in a L4-L5 XLIF at early and late fusion stages. CT data from an asymptomatic subject were segmented into anatomical regions and digitally stitched into a surface mesh of the lumbosacral spine (L1-S1). The interbody cage and posterior instrumentation (unilateral and bilateral) were inserted at L4-L5. The volumetric mesh was imported into finite element software for pre-processing, running nonlinear static solves and post-processing. Loads and micromotions at the index-level facets reduced commensurately with the extent of posterior fixation accompanying the XLIF, while load-pattern changes observed at adjacent facets may be anatomically dependent. In flexion at partial fusion, compressive stress on the cage reduced by 54% and 72% in unilateral and bilateral models respectively; in extension the reductions were 58% and 75% compared to standalone XLIF. A similar pattern was observed at full fusion. Unilateral fixation provided similar stability compared to bilateral, however there was a reduction in cage stress-risers with the bilateral instrumentation. No changes were found at adjacent discs. Posterior supplemental fixation alters biomechanics at the index and adjacent levels in a manner that warrants consideration alongside clinical information. Unilateral instrumentation is a more efficient option where the stability requirements and subsidence risk are not excessive.

Authors: Ramakrishna VA, Chamoli U, Larosa AG, Mukhopadhyay SC, Gangadhara Prusty B, Diwan AD
Year:��2023
Journal name: Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine

Abstract: Pseudo-ductile fracture in composite structures is desirable which can provide a window of detection for structural anomaly. Several design strategies had been investigated to induce pseudo-ductile fracture in thin composite laminates. However, the thickness of load bearing structures such as the grid stiffeners in advanced grid structures are ranged up to 30 mm. This paper presents an investigation into introducing pseudo-ductile fracture into a grid stiffener of representative thickness by implementing cut-tow design at the grids’ intersection. Automated fibre placement permits the cutting, terminating and restarting layup of a tow which makes this design feasible. Experimental and numerical results showed the benefits of a cut-tows design is twofold. Firstly, improvements up to 42.4 % was achieved in mechanical strength due to the reduction in tow waviness at the grid’s intersection. By varying the ratio and distribution of cut-tows, it is possible to achieve additional 55.9 % of pseudo-ductile displacement before fracture in thick section grid stiffeners under tension and bending loads. The enabling mechanism of pseudo-ductile fracture are discussed further using numerical modelling.

Authors: Cong Zhao, Matthew J. Donough, B. Gangadhara Prusty, Jun Xiao, Laishui Zhou, Luling An
Year:��2023
Journal name: Composite Structures

Abstract: Material extrusion (ME) is one of the most popular techniques for 3D printing. However, despite offering almost unlimited flexibility in the design and choice of material of the printed components, it is yet to be widely adopted in the industry. Mechanical properties of printed parts are usually below expectations and this can be caused by the presence of voids, the most commonly encountered structural defect. Besides quantity, void type, shape, size, and their location, density and distribution within the microstructure can affect the material’s mechanical properties. Detailed knowledge of void geometric characteristics is also crucial for modelling and simulation, and there is a need for comprehensive experimental derived void databases. In this work, X-ray micro-computed tomography has been utilised to image two samples printed by ME and their respective parent feedstock filaments. Voids have been identified, quantified, mapped in 3D, then individually labelled, and their key geometrical characteristics extracted and analysed. Furthermore, the effects of the printing process on voids' geometry and distribution have been qualitatively and quantitatively assessed.

Authors: S. Sommacal, A. Matschinski, J. Holmes, K. Drechsler, P. Compston
Year:��2023
Journal name: Composite Structures

Abstract: Fibre-reinforced biocomposites usage has gained prominence over the past decade. Although higher fracture toughness was observed when fibres were added to biocomposites, material degradation could occur due to filler and fibre content intolerance in the biocomposite matrix. Optimisation of resin-fibre-filler ratios helps in increasing the tribological performance of high load-bearing applications. However, the tribological performance is less understood due to limited in-vitro studies on the effect of fibre microstructures. A comprehensive investigation of the reciprocating and rotary wear behaviour of different compositions was carried out by varying fibre (0%, 5%, 10% and 15%) to particulate filler (40%, 45%, 50%, and 55%) weight fractions. The investigation aimed to identify the optimal composition of fibre-reinforced biocomposites based on the in-vitro ball-on-disc reciprocating and rotary wear tests in the presence of modified Fusayama solution. The cross-sectional areas of wear tracks were analysed using laser microscopy and scanning electron microscopy techniques to assess the surface morphology and subsurface damage of the wear tracks on biocomposites and the antagonist. The numerical results were statistically analysed using two-way ANOVA followed by a posthoc Tukey’s test (p = 0.05). The results showed a combination of adhesive, abrasive and fatigue wear for all the tested Groups. The friction coefficient had a longer transient period for the 5 wt% and 10 wt% Groups. Based on the surface roughness, coefficient of friction, SEMs, specific wear rate, and ease of manufacturing, the threshold limit for fibre loading was found to be 10 wt%. The rotary test had a considerably lower specific wear rate compared to the reciprocating test. Fibre weight fraction was found to be the influencing factor of the abrasive wear behaviour compared to fibre length for the tested Groups.

Authors: Raju, Chee Wah Loy, Kiho Cho, Paul Farrar & B. Gangadhara Prusty
Year:��2023
Journal name: Nature Scientific Reports

Abstract: Hydrogen is emerging as a promising future energy medium in a wide range of industries. For mobile applications, it is commonly stored in a gaseous state within high-pressure composite overwrapped pressure vessels (COPVs). The current state of the art pressure vessel technology, known as Type V, eliminates the internal polymer gas barrier used in Type IV vessels and instead relies on carbon fibre laminate to provide structural properties and prevent gas leakage. Achieving this functionality at high pressure poses several engineering challenges that have thus far prohibited commercial application. Additionally, the traditional manufacturing process for COPVs, filament winding, has several constraints that limit the design space. Automated fibre placement (AFP), a highly flexible, robotic composites manufacturing technique, has the potential to replace filament winding for composite pressure vessel manufacturing and provide pathways for further vessel optimisation. A combination of both AFP and Type V technology could provide an avenue for a new generation of high-performance composite pressure vessels. This critical review presents key work on industry-standard Type IV vessels alongside the current state of Type V CPV technology including manufacturing developments, challenges, cost, relevance to commercial standards and future fabrication solutions using AFP. Additionally, a novel Type V CPV design concept for a two-piece AFP produced vessel is presented.

Authors: Alexander Air, Md Shamsuddoha, B. Gangadhara Prusty
Year:��2023
Journal name: Composites Part B: Engineering

Abstract: Substantial range, handling and acceleration improvements in high-performance vehicles can be achieved by weight reduction. An important area for weight reduction on a car is the wheels. A novel prototype carbon fibre/epoxy wheel has been developed using a combination of automated fibre placement (AFP) and hand layup for the Sunswift 7 solar car. A three-piece wheel design that utilises each process where best suited has been analysed and optimised using the ANSYS ACP PrepPost suite, manufactured, and mechanically tested. The wheel disc was produced using AFP and featured selective reinforcement in the form of spokes. The AFP fibre paths for the disc have been optimised using CGTech’s VERICUT VCP and VCS to minimise gaps and overlaps, resulting in a 98.9% reduction in overlaps when compared with the unoptimised layup. The rim and tyre mounting region of the wheel have been manufactured using hand layup and adhesively bonded to the disc. This hybrid manufacturing approach has demonstrated an advancement in the feasibility of combining traditional and automated composite manufacturing. The final wheel weighed 3352 g, and the wheel deflection under a compressive load has been experimentally verified within 3% of the theoretical value.

Authors: Alexander Air, Md Shamsuddoha, Ebrahim Oromiehie & B. Gangadhara Prusty
Year:��2023
Journal name: The International Journal of Advanced Manufacturing Technology

Abstract: Innovations in recycling, automated and out-of-autoclave processes have renewed significant interests in carbon fibre - polyether ether ketone (CF/PEEK) thermoplastic composites. The crystallinity and, consequently, fracture toughness of semi-crystalline thermoplastics is affected by the cooling rates during processing. Extensive review of published data indicates that in-situ consolidation deposition rates affect PEEK crystallisation. This paper investigates the influence of automated fibre placement (AFP) deposition rates from 76 to 124 mm/s on the crystallinity and mode I fracture toughness of Cytec PEEK polymer matrix with carbon Fibre (AS4/APC2) laminates. The experimental results showed a decrease in crystallinity when the material deposition rate was increased. However, this did not translate into an improvement in fracture toughness. The preliminary study showed an increase in fracture toughness from 76 to 100 mm/s deposition rates. The 124 mm/s samples had the lowest fracture toughness despite having the lowest crystallinity. The crystallinity was not the only driving mechanism in improving the fracture toughness performance and good consolidation is an important factor as well.

Authors: Shafaq; Donough MJ; Farnsworth AL; Phillips AW; St John NA; Gangadhara Prusty B
Year:��2023
Journal name: Composites Part B: Engineering

Abstract: Composite marine propellers improve hydrodynamic efficiency by inducing bend-twist coupling and allowing for passive pitch changes. One critical limitation, however, is the extent to which a composite propeller blade can deform and cause a pitch change without incurring structural failure. Recent numerical studies showed that curvilinear tows could improve the structural response of a composite blade by lowering its deflection or stress and strain required to induce a pitch change, but no experimental validation has been carried out before. The current study, thus, presents the manufacture of composite sandwich hydrofoils made with steered tows using automated fibre placement and validates the curvilinear tow benefits. Two hydrofoils were optimised with straight and curved fibre path layups, respectively and were manufactured for mechanical testing. The manufacturing complications arising from steering curvilinear tows in a three-dimensional convex mould are also discussed in the paper. The study found that significant tow buckling occurred near the tool cavity edge due to excessive steering radius during manufacture. The follow-up structural cantilevered tests showed that the experimental results were consistent with the FE predictions despite the presence of some manufacturing defects. The experiment agreed that the hydrofoil manufactured with curved tows achieved a similar tip twist but a significant reduction in deflection and critical principal strains compared to the hydrofoil made with straight tows. The use of a foam core reduced the overall weight of the sandwich hydrofoils by about 25% compared to that of a fully-carbon composite hydrofoil, and the numerical analysis showed that the core shear failure induced by transverse shear stresses was unlikely to occur.

Authors: Maung PT; Prusty BG; Donough MJ; Oromiehie E; Phillips AW; St John NA
Year:��2023
Journal name: Marine Structures

Abstract: Thick composite laminates are often required in marine applications to resist high hydrodynamic forces. In this work, damage in thick glass-fibre/epoxy laminates caused by low velocity impacts was investigated experimentally and numerically. Cubic specimens 50 × 50 × 50 mm were manufactured, and the ply stacking directions were orientated at 0°, 22.5° and 45° to the impact plane. The impact damage was localised in the vicinity of the impactor contact area and included an interplay of fibre crushing, matrix cracks, matrix plasticity, and delaminations. Finite element modelling predicted the impact response and the type of damages. The model also quantified the primary energy absorption mechanisms which were by fibre crushing, matrix plasticity and propagation of delamination cracks. The highest impact damage resistance was obtained with the 0° (in-plane) specimen due to the fibres being aligned to the impact loading direction.

Authors: Donough MJ; Prusty BG; Van Donselaar MJ; Morozov EV; Wang H; Hazell PJ; Philips AW; John NA
Year:��2023
Journal name: International Journal of Impact Engineering

Abstract: In this work, the scaled boundary finite element method (SBFEM) is employed to model weakly bonded thick laminated composite plates subjected to bi-axial bending. A three-dimensional modelling technique incorporated in the SBFEM framework is used for thick laminated plates, where two-dimensional plate models cease to provide accurate results. Weakly bonded interfaces are modelled using spring layer models with the incorporation of zero-thickness interface elements between the layers. The interface element is subjected to behave in a linearly elastic manner capturing the slippage between the layers. Using SBFEM, it is possible to have fewer discretisation in the through thickness direction of the plate (or individual lamina) without compromising the accuracy of the results. Additionally, the size of interface elements can be kept small without altering the size of the adjoining bulk element. Validation examples covering symmetric, anti-symmetric cross ply and angle ply laminates have been solved using the proposed approach. Results from the proposed method using SBFEM are compared with well-established methods for modelling thick laminated composite under bi-axial bending.

Authors: Garg N; Donough MJ; Song C; Phillips AW; Prusty BG
Year:��2023
Journal name: Engineering Analysis with Boundary Elements

Abstract: Robotic manufacturing using automated fibre placement (AFP) provides the foundation for efficient, low labour intensive, high accuracy and repeatable composite manufacturing. This paper presents a novel manufacturing process used to build a full-scale shape-adaptive composite hydrofoil using AFP. The outer layers of the hydrofoil were made up of carbon-fibre/epoxy plies laid up by AFP. The inner core of the hydrofoil was made from an E-glass/epoxy laminate, which was used as a rotatable “core-wrap” mandrel to place the carbon plies on. This type of core-wrapping manufacturing process allowed the consolidation of continuous carbon fibres around the leading and trailing edges and minimised the risk of premature delamination failure. Fibre orientations of the AFP-laid carbon plies were optimised using a genetic algorithm for a shape-adaptive response, and the manufacturing process from the layup to the curing is presented. The manufacturing downtime, dimensional variation and AFP-inherent imperfections and underlying reasons for their occurrence were discussed for future improvement. It was found that the manufactured hydrofoil has a lower laminate thickness than the expected profile due to not using female moulds during the cure process. About half of the AFP operation time was spent on several downtimes such as ply inspection and layup rework. Intrinsic tow defects such as tow upfolding and wrinkling mostly occurred around the narrow-curvature trailing edge and contributed largely to layup rework time.

Authors: Maung PT; Prusty BG; Oromiehie E; Phillips AW; St John NA
Year:��2022
Journal name: The International Journal of Advanced Manufacturing Technology

Abstract: Thermoplastic composites boast several advantages over thermoset composites including outstanding mechanical performance, thermoformability and recyclability. Coupled with automated fibre placement and out-of-autoclave in-situ consolidation, this has driven increased interest in thermoplastic composite materials. In-situ consolidation refers to heating and consolidating the thermoplastic towpregs as they are being laid. This leverages automation to reduce the process steps, costs, and turnaround. However, in-situ consolidated thermoplastic composites by automated fibre placement have not gained wider acceptance within the industry due to ongoing concerns regarding manufacturing induced defects such as voids, poor interlaminar bonding and dimensional stability. A powerful tool available to researchers and engineers to better understand the development of such defects is process modelling. Process modelling is the analytical or numerical simulation of the in-situ consolidation process which typically involves complex interactions between the mechanical, thermal, and physical phenomena. This review paper covers the modelling approaches and material models which researchers have employed to simulate and predict the in-situ consolidation process. Experimental work on optimising the process parameters is also briefly discussed. The current limitations and future directions of process modelling for in-situ consolidation are also discussed.

Authors: Donough MJ; Shafaq ; St John NA; Philips AW; Gangadhara Prusty B
Year:��2022
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: This paper evaluates the applicability of a damage slow growth management strategy to patch repairs or bonded joints of primary aircraft structures established earlier by the authors utilising wide bonded metal joints through a computational study using MSC Marc software. The adhesive element failure criteria was applied to establish the residual static strength of the joint as a function of disbond length. A cohesive zone element model implemented in a Ucohesive subroutine was used to evaluate the strain energy release rates (SERRs) as a function of disbond crack extent and predict the disbond growth in the joint. Similar to the 2D analysis conducted in the past, the results showed that for a wide joint with sufficient static strength safety margin under a typical fatigue loading that would propagate disbond, the disbond growth would be stable within a particular length range. Therefore, the slow growth approach would be viable when the patch is modelled to be large enough to allow expanded damage growth. Furthermore, numerical results on the load redistribution effect indicate an overall significantly slower disbond growth and longer fatigue life of the joint with part width disbond than that with full-width disbond.

Authors: Tanulia V; Wang J; Pearce GM; Baker A; Prusty BG
Year:��2022
Journal name: Composites Part C: Open Access

Abstract: The entrainment abrasive waterjet machines start with a pure waterjet before abrasives are injected to avoid nozzle clogging. This pure waterjet impact is the primary cause for delamination in the form of edge pop-up of laminated composites. This paper presents an investigation into the pop-up delamination formation mechanisms. A coupled fluid–solid numerical model is developed by coupling smoothed particle hydrodynamics method and finite element method. It is found that pop-up delamination is initiated due to the material’s elastic response to a rapid release of shock pressure to stagnation pressure and the traverse shear stresses induced by the bending of the plies. A hydro wedging effect between the plies due to flow divergence propagates the delamination. There is a threshold value for the water pressure above which pop-up delamination does not increase significantly. Moreover, the smallest delamination area takes place on the [0]12 composite, followed by the [0/45/90/-45/0/45]s and [0/90]3s composites.

Authors: Gu Y; Nguyen T; Donough MJ; Gangadhara Prusty B; Wang J
Year:��2022
Journal name: Composite Structures

Abstract: Objectives: To assess the hypotheses that a restored tooth structure for a class II occlusal-distal (OD) cavity can be reinforced by optimizing the cavity geometry and choosing composites with adequate mechanical properties. Methods: A human maxillary molar tooth was scanned, and segmented. The 2D profiles of dentin and enamel were drawn and imported to ABAQUS software. Eighteen restored tooth models with different cavity occlusal depths (OcDs) and internal cavity angles were developed. A semi-circular stone part was used to apply contact loads to the restored tooth model. After setting up the required interactions and boundary conditions, a written Python code was used to automatically assign a wide range of elastic moduli, from 2 GPa to 26 GPa, to the composite restorations, and assign constant material properties to the enamel and dentine.For simplicity, the behaviour of the mechanical material was postulated homogeneous and elastic, while the FE analyses were linearly carried out in this study. Also, the code enabled the FEA software to conduct the stress analyses, determine maximum principal stresses, and record the obtained results. Results: The internal cavity angle formed between the mesial wall and the pulpal floor of the cavity significantly changed the peak maximum principal stress both in the enamel and restoration. The peak stress concentrations were observed mostly at the enamel-restoration interface, with an almost perpendicular orientation to this interface. Regarding the effect of occlusal cavity depth (OcD), the model with the shallowest cavity (OcD = 1.5 mm) represented greater resistance to applied loads than the model with deeper cavities (OcD = 2.0 mm and OcD 2.5 mm). The composite modulus (CM) in the range of 10–18 GPa reduced the maximum principal stress concentrations in the enamel. The lowest result for maximum principal stress was observed in the model with OcD = 1.5 mm, CM = 10 GPa and internal cavity angles = 100°, which was the strongest model against contact loads. Significance: Class II OD cavities with optimal geometry have reduced induced stress levels, thus being able to be more mechanically robust against contact load transmitted by a stone. Cavity geometry designs with obtuse (more than 90°) internal cavity angles were significantly efficient in minimizing peak stress concentrations. The results indicated that for the model with obtuse internal cavity angles, choosing a composite with optimised properties can diminish stress, particularly at the tooth-restoration interface. Furthermore, the shallowest the cavity, the sturdier the restoration was, especially when the interface tooth-restoration laid on enamel and not on dentine.

Authors: Babaei B; Cella S; Farrar P; Prentice L; Prusty BG
Year:��2022
Journal name: Journal of the Mechanical Behavior of Biomedical Materials

Abstract: In-vivo experimental techniques to understand the biomechanical behavior of a restored tooth, under varying oral conditions, is very limited because of the invasive nature of the study and complex tooth geometry structure. Therefore, 3D-Finite element analyses are used to understand the behavior of a restored tooth under varying oral conditions. In this study, the distribution of maximum principal stress (MaxPS) and the location of MaxPS on a restored tooth using six different commercially available dental resin composites under the influence of thermal and thermomechanical stimuli are performed. An intact tooth was scanned using µ-CT and segmented to obtain separate geometric models of the tooth, including enamel and dentine. Then, a class II mesial-occlusal-distal (MOD) cavity was constructed for the tooth model. The restored tooth model was further meshed and imported to the commercial Finite Element (FE) software ANSYS. Thermal hot and cold stimuli at 50 °C and 2 °C, respectively, were applied on the occlusal and lingual surface of the tooth model with the tooth’s ambient temperature set at 37 °C. A uniform loading of 400 N was applied on the occlusal surface of the tooth to imitate the masticatory forces during the cyclic thermal stimuli. The results of this study showed that the restorative materials with higher thermal conductivity showed a lower temperature gradient between the restoration and enamel, during the application of thermal stimuli, leading to a higher value of MaxPS on the restoration. Moreover, on applying thermal stimuli, the location of MaxPS at the restoration-enamel junction (REJ) changes based on the value of the coefficient of thermal expansion (CTE). The MaxPS distribution on the application of simultaneous thermal and mechanical stimuli was not only dependent on the elastic modulus of restorative materials but also their thermal properties such as the CTE and thermal conductivity. The weakest part of the restoration was at the REJ, as it experienced the peak stress level during the application of thermomechanical stimuli. The findings from this study suggest that restorative materials with lower values of elastic modulus, lower coefficient of thermal expansion and higher values of thermal conductivity result in lower stresses on the restoration. The outcomes from this study also suggest that the thermal and mechanical properties of a restorative material can have a considerable effect on the selection of restorative materials by dental clinicians over conventional restorative materials.

Authors: Jerrin Thadathil Varghese, Behzad Babaei, Paul Farrar, Leon Prentice, B. Gangadhara Prusty
Year:��2022
Journal name: Dental Materials

Abstract: This experimental investigation explored the optimisation of silane treatment of surface-modified S-2 Glass fibres in restorative dental composites for improved mechanical performance. The influence of optimum amount of silane to improve the interfacial adhesion at the fibre-matrix interfaces and its effect on the mechanical properties of the restorative composites were explored. S-2 Glass fibres of 5 μm diameter and 250 μm length were surface modified using the acid etching technique. The etched fibres were then treated with either 3-methacryloxypropyltrimethoxysilane (3-MPS), 3-Glycidoxipropyltrimethoxysilane (3-GPS) or 8-methacryloxyoctyltrimethoxysilane (8-MOTS) at varying molar % / wt% concentrations. Fibres that were not silanised with any silane coupling agents were used as the control sample. The silanol content of each mixed silane was observed using Fourier transform infrared (FT-IR) spectroscopy analysis. Fibres (5 wt%) with optimised molar% / wt% silane coupling concentration were added to UDMA/TEGDMA dental resin. Mechanical properties such as flexural strength, flexural modulus, and the breaking energy of the materials were evaluated using a comprehensive experimental programme. FTIR spectrum of glass fibre silanised with each silane coupling agent revealed many peaks from 3800 to 1400 cm−1, indicative of -CH3, -CH2, and Cdouble bondO bonding, suggesting the proper silanization of the fibre. The contact angle test revealed that optimum wt% concentration of 3-MPS, 3-GPS and 8-MOTS were 0.5%, 0.8% and 1.4% respectively. The flexural strength of the fibre-reinforced with optimum concentration of 3-MPS (DC-3-MPS_0.5%) increased by 7.0% compared to those of the 2 wt% concentration of 3-MPS fibre-reinforced composite (DC-3-MPS_2.0%). While the flexural strength of optimum concentration 8-MOTS grafted dental resin composites (DC-8-MOTS_1.4%) were 9.9% higher than that of 2 wt% concentration 8-MOTS grafted dental resin composite (DC-8-MOTS_2.0%) and the flexural strength of optimum concentration of 3-GPS (DC-3-GPS_0.8%) was 7.5% higher when compared to that of 2 wt% concentration 3-GPS grafted dental resin composites (DC-3-GPS_2.0%). A concurrent trend was found while investigating the fracture behaviour of the dental composite with optimum wt% concentration of each silane coupling agent against its corresponding higher wt% concentrations. The ANOVA results showed that the optimum fibre-reinforced dental composites grafted with 8-MOTS showed better mechanical behaviour when compared to 3-GPS and 3-MPS. The interfacial adhesion between the fibre and the resin due to silane coupling agents has helped to improve the mechanical properties of the fibre-reinforced dental composite. This is the first experimental study to provide a thorough investigation into the significance of the optimal use of silane coupling agents to treat the S-2 Glass fibres and subsequently the influence on the mechanical performance of the fibre-reinforced flowable dental composites.

Authors: Jerrin Thadathil Varghese, Kiho Cho, Raju, Paul Farrar, Leon Prentice, B. Gangadhara Prusty
Year:��2022
Journal name: Dental Materials

Abstract: To assess the hypotheses that a restored tooth structure for a class II occlusal-distal (OD) cavity can be reinforced by optimizing the cavity geometry and choosing composites with adequate mechanical properties. A human maxillary molar tooth was scanned, and segmented. The 2D profiles of dentin and enamel were drawn and imported to ABAQUS software. Eighteen restored tooth models with different cavity occlusal depths (OcDs) and internal cavity angles were developed. A semi-circular stone part was used to apply contact loads to the restored tooth model. After setting up the required interactions and boundary conditions, a written Python code was used to automatically assign a wide range of elastic moduli, from 2 GPa to 26 GPa, to the composite restorations, and assign constant material properties to the enamel and dentine. For simplicity, the behaviour of the mechanical material was postulated homogeneous and elastic, while the FE analyses were linearly carried out in this study. Also, the code enabled the FEA software to conduct the stress analyses, determine maximum principal stresses, and record the obtained results. The internal cavity angle formed between the mesial wall and the pulpal floor of the cavity significantly changed the peak maximum principal stress both in the enamel and restoration. The peak stress concentrations were observed mostly at the enamel-restoration interface, with an almost perpendicular orientation to this interface. Regarding the effect of occlusal cavity depth (OcD), the model with the shallowest cavity (OcD = 1.5 mm) represented greater resistance to applied loads than the model with deeper cavities (OcD = 2.0 mm and OcD 2.5 mm). The composite modulus (CM) in the range of 10–18 GPa reduced the maximum principal stress concentrations in the enamel. The lowest result for maximum principal stress was observed in the model with OcD = 1.5 mm, CM = 10 GPa and internal cavity angles = 100°, which was the strongest model against contact loads.Class II OD cavities with optimal geometry have reduced induced stress levels, thus being able to be more mechanically robust against contact load transmitted by a stone. Cavity geometry designs with obtuse (more than 90°) internal cavity angles were significantly efficient in minimizing peak stress concentrations. The results indicated that for the model with obtuse internal cavity angles, choosing a composite with optimised properties can diminish stress, particularly at the tooth-restoration interface. Furthermore, the shallowest the cavity, the sturdier the restoration was, especially when the interface tooth-restoration laid on enamel and not on dentine.

Authors: Behzad Babaei, Suelen Cella, Paul Farrar, Leon Prentice, B. Gangadhara Prusty
Year:��2022
Journal name: Journal of the Mechanical Behavior of Biomedical Materials

Abstract: This paper investigates the bend-twist coupling analysis of multi-layered stepped generally orthotropic composite beams subjected to mixed end-of-beam and mid-span supports. Specifically, an analytical closed-form model was developed based on first-order shear deformation theory (FSDT), which discretizes the domain into elements based on the step change of geometry, laminate configuration, or mid-span boundary supports. Hamilton's principle was used to derive the governing equations within each element and connection and boundary equations. The state-Space approach was then utilized to provide an analytical solution. Moreover, an experimental investigation was conducted to validate the mode shapes and natural frequencies of the beam subjected to several mixed boundary conditions. The results are also validated with the literature and a finite element model developed using ANSYS. Comparisons demonstrate the reliability and accuracy of the analytical model.

Authors: Saeed Fazeli, Chris Stokes-Griffin, J. Gilbert, Paul Compston
Year:��2022
Journal name: Composite Structures

Abstract: The architectural intricacy of multi-ply woven composites, caused by differences in layer alignment, introduces complexity into their mesoscale response to on- and off-axis tensile loading. To better understand the relationship between architecture and deformation response, this work combines digital image correlation (DIC) and 3D micro-computed tomography (μCT) to examine deformation for 0°, 15°, 30° and 45° specimens. Tensile tests were conducted with a four-layer plain woven carbon/polyetheretherketone (C/PEEK) laminate. In addition to the evident variance of mechanical properties between orientations, significant mesoscale differences in topography and strain were observed resulting from the layer alignment of individual specimens. Alignment of the top two surface layers induced distinct topographical peaks under extension, whereas nested architectures formed continuous topographical ridges. Matching observed surface strains around microstructural cracks identified in μCT images revealed both inter-tow and intra-tow shearing during off-axis extension and corresponding fibre reorientation, which effectively illustrates the potential benefits from combining DIC and μCT.

Authors: John Holmes, Silvano Sommacal, Raj Das, Zbigniew Stachurski, Paul Compston
Year:��2022
Journal name: Composites Part B: Engineering

Abstract: Dental resin composites have revolutionized dental care and enabled minimally invasive dentistry to preserve healthy tooth structure and provide natural-appearing esthetic results; these materials are now good alternatives to metal and amalgam restorations. Nevertheless, dental composites are being further developed to enhance their long-term clinical performance and longevity. With a complete understanding of the various material characteristics and design strategies of dental composite systems, frontiers of dental restoration research can aim towards creating novel materials that can produce very similar properties, functionalities, and internal structures as hard dental tissues. In this review article, the authors present an overview of the synthesis of the advanced dental composite systems with the recent research and development fields over the last 5 years. This review also explores how to control and optimize the required properties of the composites, ideally to increase the longevity/durability of restorations preventing recurrent caries. Research studies and commercial products are introduced to forecast the demands and trends of resin-based dental composites, in order to assist clinicians and researchers in optimal selection of materials to fulfill mechanical, physical, biological, and functional requirements.

Authors: Kiho Cho, Ginu Rajan, Paul Farrar, Leon Prentice, B. Gangadhara Prusty
Year:��2022
Journal name: Composites Part B: Engineering

Abstract: This study reports the findings on the impact behaviour of metal-composite structures. Carbon fibre/Epoxy composite laminates were manufactured by using the Automated Fibre Placement (AFP) technique. Subsequently, hybrid structures were fabricated by bonding fibre laminate and aluminium plate together. The hybrids were tested at low velocity impact energies to probe the role of AFP composite laminates on the performance of the hybrid system. Our findings show that the bonding of the composite onto aluminium plate increased the natural frequency (stiffness) of the system and its energy absorption capability by almost 40 %. It was also found that the fibre layout of AFP composite significantly improved the central deflection of the hybrid. For instance, the deflection of cross-ply hybrids was 15% less in comparison to their counterparts with unidirectional fibrous composites. Nevertheless, under the investigated energies, the fibre layout appeared to have a marginal influence on the peak contact force. Post-mortem examination showed that at an impact energy of 150 J there was no fibre failure observed in asymmetric FMLs with unidirectional composite laminates. Conversely, the fibre failure in cross-ply hybrids occurred at 150 J. This suggests that less energy is required to induce fibre failure energy in cross-ply hybrids when compared to their unidirectional hybrid counterparts. Furthermore, it was also found that substrate treatment was successful in preventing excessive delamination, even though its influence on the peak contact force was not significant.

Authors: Arcade Serubibi, Paul Hazell, J.P. Escobedo, H. Wang, Ebrahim Oromiehie, Gangadhara Prusty
Year:��2021
Journal name: Materials Today Proceedings

Abstract: This study reports the findings on the impact behaviour of metal-composite structures. Carbon fibre/Epoxy composite laminates were manufactured by using the Automated Fibre Placement (AFP) technique. Subsequently, hybrid structures were fabricated by bonding fibre laminate and aluminium plate together. The hybrids were tested at low velocity impact energies to probe the role of AFP composite laminates on the performance of the hybrid system. Our findings show that the bonding of the composite onto aluminium plate increased the natural frequency (stiffness) of the system and its energy absorption capability by almost 40 %. It was also found that the fibre layout of AFP composite significantly improved the central deflection of the hybrid. For instance, the deflection of cross-ply hybrids was 15% less in comparison to their counterparts with unidirectional fibrous composites. Nevertheless, under the investigated energies, the fibre layout appeared to have a marginal influence on the peak contact force. Post-mortem examination showed that at an impact energy of 150 J there was no fibre failure observed in asymmetric FMLs with unidirectional composite laminates. Conversely, the fibre failure in cross-ply hybrids occurred at 150 J. This suggests that less energy is required to induce fibre failure energy in cross-ply hybrids when compared to their unidirectional hybrid counterparts. Furthermore, it was also found that substrate treatment was successful in preventing excessive delamination, even though its influence on the peak contact force was not significant.

Authors: V. Zinnecker, S. Madden, C. Stokes-Griffin, P. Compston, A.V. Rode, L. Rapp
Year:��2022
Journal name: Optics & Laser Technology

Abstract: The nanomechanical characterisation of unidirectional carbon fibre (CF) reinforced polyether ether ketone (PEEK) composites using a robotic processing technology known as automated fibre placement (AFP) with different processing conditions is presented in this paper. Mechanical and microstructural analysis revealed that a consolidated structure can be obtained when CF-PEEK is manufactured at high temperature. Later, nanoindentation test confirmed that CF-PEEK manufactured at higher hot gas torch (HGT) temperature and larger consolidation force exhibited increased nanohardness, elastic modulus and creep resistance either in polymer matrix or fibre/matrix interface in comparison with the laminates manufactured at lower HGT temperature of 650 °C. The nanohardness values in polymer matrix and fibre/matrix interface of CF-PEEK composites manufactured at 950 °C with 350 N consolidation force were about 188.8 and 1297.7 MPa while their values of composites manufactured at 650 °C were about 173.2 and 1077.6 MPa, respectively.

Authors: Asit Kumar Gain, Ebrahim Oromiehie, B. Gangadhara Prusty
Year:��2022
Journal name: Composites Communications

Abstract: Fibre reinforced composites materials offer a pathway to produce passive shape adaptive smart marine propellers, which have improved performance characteristics over traditional metallic alloys. Automated fibre placement (AFP) technology can provide a leap forward in cyber-physical automated manufacturing, which is essential for the implementation and operation of smart factories in the marine propeller industry towards Industry 4.0 readiness. In this paper, a comprehensive structural health monitoring routine was performed on an AFP full-scale composite hydrofoil to gain confidence in its dynamic and structural performances through a number of active and passive sensors. The hydrofoil was subjected to constant amplitude flexural fatigue loading in a purpose-built test rig for 105 cycles. The hydrofoil was embedded with distributed optical fibre sensors, traditional electrical strain gauges and linear variable displacement transducers. Both microelectromechanical system and piezoelectric accelerometers were used to conduct experimental modal analyses to observe changes in the modal response of the hydrofoil at regular intervals throughout the fatigue program. The hydrofoils modal response, as well as the stiffness measured using both displacements and strains, remained unchanged over the fatigue loading regime demonstrating the structural integrity of the hydrofoil. The optical fibre sensors endured the fatigue test cycles showing their robustness under fatigue loads. Furthermore, the sensing systems demonstrated the potential of being utilised as a useful maintenance tool combining their adaptability with automated manufacturing during manufacturing through integration within the hydrofoil, a structural test framework for performance measurement, data acquisition and analytics for visualisation, and the prospect of decision making for maintenance requirement during any onset in structural performance.

Authors: Md Shamsuddoha, Gangadhara Prusty, Phyo Thu Maung, Andrew W Phillips and Nigel A St John
Year:��2021
Journal name: Smart Materials and Structures

Abstract: Composites are potential replacement materials for marine propellers due to their benefits including high strength-to-weight ratio, high environmental and fatigue resistance, damping, and design flexibility. Underwater composite structures are susceptible to low-velocity impacts with floating or submerged debris, underwater cables, ice, marine animals, collision with other crafts and docks as well as groundings. Being a critical structural component, a propeller's durability is essential and must provide resistance to impact damage. The impact behaviour of a marine composite propeller is highly complex, and predominant influencing factors are identified and discussed in this review paper. These include laminate curvature, laminate thickness, impact angle, inter-ply stacking sequence, constituent materials, water diffusion, fluid-structure interaction, among others. The main objective of this review is to bring together the findings of many relevant publications on the impact mechanics of composite structures and to discuss their findings from the perspective of composite marine propeller design to improve impact behaviour.

Authors: Faisal Islam, Rowan Caldwell, Andrew W. Phillips, Nigel A. St John, B. Gangadhara Prusty
Year:��2022
Journal name: Composites Part C: Open Access

Abstract: The applicability of a damage slow growth management strategy to bonded joints/patch repairs of primary aircraft structures was evaluated through an experimental and computational study. Fatigue tests were conducted to investigate the entire process of disbond growth from initiation up to joint ultimate failure. The residual static strength of the joint as a function of disbond length was established using finite element modelling, in which the mesh size was calibrated using the static strength of the specimens measured in room temperature and dry (RD) and hot-wet (HW) conditions, based on the characteristic distance approach. A virtual crack close technique (VCCT) approach was utilised to assess the strain energy release rates (SERRs) as a function of disbond crack length. The measured disbond growth rates were correlated with the SERRs using a modified Paris law that enabled prediction of joint fatigue life. The fatigue test results indicated that for a joint having a sufficient static strength safety margin under a typical fatigue loading that would propagate disbond, the disbond growth would be stable in a particular length range. Thus, the slow growth approach would be feasible for a bonded joint/patch repairs if the patch is designed to be sufficiently large to allow extended damage propagation (whilst in the case when patch size must be limited, safe-life design for the patch termination region in critical repairs must be considered. Should disbond growth occur in this case, the joint must be repaired or replaced). The work presented in this paper validated the framework/procedure proposed previously by the authors (Tanulia et al., 2020) for managing damage slow growth in bonded joints/patch repairs. In the last part of this paper the planned follow-on research is briefly described.

Authors: Veldyanto Tanulia, John Wang, Garth M. Pearce, Alan Baker, Paul Chang, B. Gangadhara Prusty
Year:��2022
Journal name: International Journal of Fatigue

Abstract: This paper presents an efficient and novel cohesive contact network approach, modelling multiple mesoscale composite failures including delamination, matrix cracking, and fibre rupture within large assemblies, such as the tow-wise assembled automated fibre placement or filament wound composites. The various failure modes are modelled by allocating cohesive contact interfaces with different input parameters along or perpendicular to the fibre axis, forming an interconnected cohesive contact network. The strict element size requirement of damage modelling in traditional methods is significantly alleviated with the use of an advanced segment-to-segment contact formulation. This method allows for greater mesh sizes at the crack front (comparable to the cohesive zone length) which opens up the possibility of modelling multiple potential failures at the sub-component or even structural level with current computational resources. Several numerical studies including double cantilever beam, end notched flexure, fixed ratio mixed mode, and quasi-isotropic laminate tension are carried out to demonstrate the feasibility and efficiency of the proposed approach. The matrix cracking and delamination, as well as their interactions, which ultimately lead to fibre rupture are properly captured. The global response and final damage pattern also show an excellent agreement with the published numerical and experimental results.

Authors: Xie Li, Sonya A. Brown, Mathew W. Joosten, Garth M. Pearce
Year:��2022
Journal name: Composite Structures

Abstract: Experimental demonstration and performance evaluation on a shape-adaptive carbon composite full-scale hydrofoil manufactured using automated fibre placement (AFP) are presented in this paper. The experimental responses of the hydrofoil are validated with the finite element analysis (FEA) tools. The static performance of the hydrofoil was investigated using quasi-static cantilever load, whereas the dynamic response was studied using experimental modal analysis (EMA) to assess the structural quality of the manufactured hydrofoil. The variation between predicted and experimental modal and bending stiffness was found to be within 20%. Structural strains were also monitored using a network of distributed fibre optic sensors on the surface as well as embedded in conjunction with a network of strain gauges. The outcomes from this work demonstrates a framework of numerical analysis and experimental validation techniques using multiple sensors, which will pave the way towards further demonstrating the structural adequacy and performance of such hydrofoil, made of automated techniques and embedded with optical fibre sensor systems.

Authors: Phyo Thu Maung, B. Gangadhara Prusty, Md Shamsuddoha, Andrew W. Phillips, Nigel A. St John
Year:��2022
Journal name: Composites Part C: Open Access

Abstract: The automated fibre placement (AFP) process is a complex manufacturing technique with many variables which affect the final part quality. Inverse Machine Learning (ML) models can be used as decision-aid tools for optimising thermoplastic composites manufacturing. However, a common challenge of ML application in manufacturing is the acquisition of relevant and sufficient data. To overcome this small-data learning problem, a hybrid approach has been proposed here which combines the benefits of ML algorithms such as the Artificial Neural Networks (ANN), virtual sample generation (VSG) methods, physics-based numerical simulations and data obtained from experiments and photonic sensors, to enhance the manufacturing process.

Authors: Faisal Islam, Chathura Wanigasekara, Ginu Rajan, Akshya Swain, B. Gangadhara Prusty
Year:��2022
Journal name: Manufacturing Letters

Abstract: This paper presents a model to predict local fibre angle change due to post-forming of polyamide 6 carbon (CF/PA6) thermoplastic tubular structures. Fibre angles of the CF/PA6 tubes after forming are predicted based on the initial local fibre angles before forming within their bending zones. Four sets of CF/PA6 tubes were uniformly heated to 220 °C and formed under isothermal conditions into 45°, 90°, 135° and 180° bends using a rotary draw bender with a bending ratio of 2. A model is derived to predict local post-forming fibre angle changes and validated by experimental fibre angle measurements taken both before and after forming with an optical measurement system. Additionally, micro computed tomography is performed to analyse post-formed tube geometries and determine post-forming strains. The fibre angle prediction model allows laminate mechanical analysis to be performed on post-formed tube, therefore enabling tube laminate design optimisation.

Authors: Mengyuan Li, Chris Stokes-Griffin, Silvano Sommacal, Paul Compston
Year:��2022
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: This paper address the challenges in using traditional film inserts specific to hot gas torch (HGT) assisted and in-situ consolidated automated fibre placement (AFP) manufactured double cantilever beam (DCB) and end notched flexure (ENF) specimens using carbon fibre (CF) reinforced polyetheretherketone (PEEK) prepregs. Traditional films suffer from thermal degradation, wrinkling and distortion under the consolidation roller. In this study, steel shim inserts with different thicknesses (25 and 50 µm) were used to manufacture the DCB and ENF specimens for fracture toughness evaluation. The processing parameters for in-situ consolidation were selected based on prior optimisation studies on short beam tests. In-situ consolidated specimens suffer from high void content which can affect the mechanical properties. Hence, optical micrography was used to investigate on the void contents in the manufactured specimens. Microhardness measurement is proposed as an AFP manufacturing quality assessment tool for DCB and ENF specimens which were taken from different regions of composite laminates. A manufacturing methodology for producing high quality DCB and ENF specimens by hot gas torch assisted in-situ consolidation using AFP is proposed in this paper that provide comparable results with those specimens manufactured using traditional methods.

Authors: Ebrahim Oromiehie, Asit Kumar Gain, Matthew J. Donough, B. Gangadhara Prusty
Year:��2022
Journal name: Composite Structures

Abstract: This paper address the challenges in using traditional film inserts specific to hot gas torch (HGT) assisted and in-situ consolidated automated fibre placement (AFP) manufactured double cantilever beam (DCB) and end notched flexure (ENF) specimens using carbon fibre (CF) reinforced polyetheretherketone (PEEK) prepregs. Traditional films suffer from thermal degradation, wrinkling and distortion under the consolidation roller. In this study, steel shim inserts with different thicknesses (25 and 50 µm) were used to manufacture the DCB and ENF specimens for fracture toughness evaluation. The processing parameters for in-situ consolidation were selected based on prior optimisation studies on short beam tests. In-situ consolidated specimens suffer from high void content which can affect the mechanical properties. Hence, optical micrography was used to investigate on the void contents in the manufactured specimens. Microhardness measurement is proposed as an AFP manufacturing quality assessment tool for DCB and ENF specimens which were taken from different regions of composite laminates. A manufacturing methodology for producing high quality DCB and ENF specimens by hot gas torch assisted in-situ consolidation using AFP is proposed in this paper that provide comparable results with those specimens manufactured using traditional methods.

Authors: Ebrahim Oromiehie, Asit Kumar Gain, Matthew J. Donough, B. Gangadhara Prusty
Year:��2022
Journal name: Composite Structures

Abstract: Advanced grid structures can realise significant weight savings, compared to conventional stringer stiffened structures. Overlaps of the transverse tows create fibre drop-off around the intersection region. As a result, this creates a potential weak point of whole advanced grid stiffened structures. Localised buckling at the intersection region is imminent under compressive loading. In order to overcome this shortfall, an automated fibre placement based method to improve the microstructure of grid stiffener is proposed in this paper. In this method, discontinuous plies are introduced into rib to remove excessive material at the intersection. The influences of fibre waviness and discontinuous plies on the microstructure, mechanical performance of grid stiffener are investigated using experimental and finite element methods. Results show that structural efficiency of grid stiffener can be improved significantly with appropriate ratio of discontinuous plies in the intersection of grid stiffener. Corresponding finite element models are developed for verification and established good correlation with the experimental response. The finite element analyses also provide an insight on the failure mechanisms. The results of this study can be further used towards the design and manufacture of practical grid stiffeners for the mechanical performance improvement.

Authors: Cong Zhao, Matthew J. Donough, B. Gangadhara Prusty Jun Xiao
Year:��2021
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: Composite tubes are used in numerous applications including aerospace, mechanical, civil and transport sectors, where they may be susceptible to combined loading especially axial compression and torsion and suffer failure due to their intrinsic weakness under such loads. An experimental cum numerical investigation is performed to understand the behaviour of hollow composite tubes with cut-outs under combined axial compression and torsional loadings. Carbon fibre reinforced thermoplastic CF/PEEK tubes with different diameters and varied lay-up sequences, were robotically manufactured using an Automated Fibre Placement (AFP) machine. These specimens were mechanically tested using a novel biaxial test jig, designed specifically to be compatible with an INSTRON 8852 axial/torsion servo hydraulic test system. A standard acrylate coated optical fibre was affixed on the surface of the cylinder for distributed strain sensing using an optical backscatter reflectometer (OBR) interrogator to obtain spatial strain data. Surface strains measured using distributed optical fibre sensing (DOFS) and strain rosettes were compared against finite element analysis predictions to successfully validate the numerical model created using Ansys ACP Pre-Post simulation package. Directional deformations around the cut-outs of these tubes were also numerically characterised and compared with digital image correlation (DIC) results from the experimental tests.

Authors: Md. Shamsuddoha, Matthew David, Ebrahim Oromiehie, B. Gangadhara Prusty
Year:��2021
Journal name: Composite Structures

Abstract: Experimental investigation is carried out to determine the flowability and stickiness of the developed composite material for dental restoration containing low aspect ratio (AR ≤ 100) surface treated micro-sized glass fibres. Specimens are manufactured by mixing low AR (50/70/100) micro-sized glass fibres with two different weight fractions (5%/10%) into UDMA/TEGDMA based resin. Particulate filler composite (PFC) containing 55% glass fillers is used as the control group. Dynamic oscillatory strain sweep tests are conducted to analyse the linear viscoelastic behaviour. Solid-to fluidic transition behaviour of dental composites is also calculated in terms of flow and yield stresses. Furthermore, the oscillatory frequency sweep tests are conducted at three different strains (0.5%, 5% and 50%) resembling the positioning of unset paste onto restorations for different real-life clinical situations. Additionally, stickiness of dental composites with handling instrument (steel) and dentine covered with bonding agent is also evaluated. The results suggested the all the FRC groups exhibited non-Newtonian, shear-thinning behaviour. It is further established that inclusion of 5% of 50/70AR fibres into dental composites does not affect the flowability. Simultaneously, stickiness with dentine covered with bonding agent is more for these two compositions as compared to that of handling instrument (steel). This study suggest that visco-elastic properties of dental composites are greatly affected by the type of filler (spherical shaped particulate fillers or rod-shaped fibres) as well as fibre weight fraction/fibre AR. This phenomenon can be attributed to the varying interactions between micro-sized fibres of different AR/weight fraction, particulate fillers and monomers.

Authors: Sonam Behl, Abbas Darestani, Farahani, Raju, Ginu Rajan, Ayman Ellakwa, Paul Farrar, Pall Thordarson, B. Gangadhara Prusty
Year:��2021
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: Carbon fiber reinforced polymer (CFRP) composites have been gathering a lot of interest in several engineering applications because of their favorable properties including lightweight and ease of manufacturing. Robotic manufacturing techniques using automated fiber placement (AFP) for aerospace and automotive applications present a growing trend toward error-free manufacturing. AFP manufactured laminates can be prone to internal flaws due to improper selection of manufacturing process parameters. Additionally, internal damage in composite laminates can occur during the operational service of the laminate due to fatigue or foreign object impacts. Identifying and characterizing at the microscopic level may allow optimization of process parameters, leading to higher quality laminates. In this paper, a direct 3D imaging approach to characterize global and local deformation-induced defects in AFP manufactured CFRP laminates using X-ray CT techniques is presented. The investigations are conducted on two sets of thermoplastic PEEK composite laminates (undeformed and deformed) manufactured using a set of processing conditions. The presented approach to quantify the defects provides local and global statistics including the evolution of local 3D fiber orientation as a methodology to detect the degree of deformation.

Authors: Ji-Youn Arns, Ebrahim Oromiehie, Christoph Arns, B. Gangadhara Prusty
Year:��2021
Journal name: Materials and Manufacturing Processes

Abstract: A strain profile measurement technique using a chirped fibre Bragg grating (CFBG) sensor by implementing an integration of differences (IOD) method is reported in this paper. Using the IOD method the spatial distribution of strain along the length of the CFBG is extracted from its power reflectance spectra. As a proof of concept demonstration, the developed technique is applied to measure the polymerisation shrinkage strain profile of a photo-cured polymer dental composite which exhibits a non-uniform strain distribution attributed to the curing lamp characteristics. The result from the CFBG technique is compared with that of an FBG array embedded in the dental composite and is correlated with the degree of conversion of the material which also depends on the curing lamp intensity distribution. This technology will have significant impact and applications in a range of medical, materials and engineering areas where strain or temperature gradient profile measurement is required in smaller scales.

Authors: Ginu Rajan, Alex Wong, Paul Farrar & Gangadhara B. Prusty
Year:��2021
Journal name: Scientific Reports

Abstract: Manufacturing of thermoplastic composites using automated fibre placement (AFP) machine with specific characteristics is a challenging task due to the interdependence of various processing conditions and variables. It is of interest to know the accurate value of different input variables which would give the desired characteristics (outputs) of the laminates. This problem comes under the framework of inverse identification and is often ill-posed and its solution becomes increasingly difficult when the available data samples are very less. The present study develops a neural network-based inverse predictive model for AFP based manufacturing process using virtual sample generation (VSG) techniques. The efficacy of the developed predictive inverse model has been established considering varieties of experimental data. The proposed approach can be applied to a large class of manufacturing processes to determine the input conditions to a get product with desired characteristics.

Authors: Chathura Wanigasekara, Ebrahim Oromiehie, Akshya Swain, B. Gangadhara Prusty, Sing Kiong Nguang
Year:��2021
Journal name: Journal of Industrial Information Integration

Abstract: Distributed fibre optic sensors (DFOS) are popular for structural health monitoring applications in large engineering infrastructure because of their ability to provide spatial strain measurements continuously along their lengths. Curved paths, particularly semicircular paths, are quite common for optical fibre placement in large structures in addition to straight paths. Optical fibre sensors embedded in a curved path configuration typically measure a component of strain, which often cannot be validated using traditional approaches. Thus, for most applications, strain measured along curved paths is ignored as there is no proper validation tool to ensure the accuracy of the measured strains. To overcome this, an analytical strain transformation equation has been developed and is presented here. This equation transforms the horizontal and vertical strain components obtained along a curved semicircular path into a strain component, which acts tangentially as it travels along the curved fibre path. This approach is validated numerically and experimentally for a DFOS installed on a steel specimen with straight and curved paths. Under tensile and flexural loading scenarios, the horizontal and vertical strain components were obtained numerically using finite element analysis and experimentally using strain rosettes and then, substituted into the proposed strain transformation equation for deriving the transformed strain values. Subsequently, the derived strain values obtained from the proposed transformation equation were validated by comparing them with the experimentally measured DFOS strains in the curved region. Additionally, this study has also shown that a localised damage to the DFOS coating will not impact the functionality of the sensor at the remaining locations along its length. In summary, this paper presents a valid strain transformation equation, which can be used for transforming the numerical simulation results into the DFOS measurements along a semicircular path. This would allow for a larger scope of spatial strains measurements, which would otherwise be ignored in practice.

Authors: Nagulapally P, Shamsuddoha M, Rajan G, Djukic L, B. Prusty G
Year:��2021
Journal name:������Բ��ǰ���

Abstract: Woven composites have complex deformation and damage behaviour which surface-based characterisation methods struggle to capture. This work combines surface digital image correlation (DIC) with 3D micro-computed tomography (μCT) and corresponding digital volume correlation (DVC) as a non-contact approach to assess the deformation and damage of woven thermoplastic composites. Specimens underwent load-relaxation tensile tests to 90% ultimate extension, inducing micro-scale damage and modest permanent architectural deformation. Results showed that differences in the loading direction and corresponding fibre waviness cause significant differences in surface topography, strain, and internal out-of-plane deformation. The average internal εz that remained after loading was 0.32% (warp) and 1.54% (weft). μCT images of specimen microstructure combined with DIC allowed depth-wise examination of surface features such as transverse cracking. DVC and μCT are effective tools for characterising woven composite deformation, imperceptible to surface-based methods, and have significant future potential for improving finite element simulations.

Authors: John Holmes, Silvano Sommacal, Zbigniew Stachurski, Raj Das, Paul Compston
Year:��2021
Journal name: Composite Structures

Abstract: To test the hypothesis that restoration of class II mesio-occlusal-distal (MOD) cavities can be strengthened through judicious choice of restoration geometry and material properties. An intact extracted human maxillary molar tooth was digitized, segmented, reconstructed, and four 3D restored tooth models were developed with four different restoration geometries: one straight, one single-curved, and two double-curved. Stress analysis was conducted for representative loading using finite element analysis, and maximum principal stresses were determined at the dentine-enamel and restoration-enamel junctions. A range of restorative material elastic moduli (5–80 GPa) and Poisson's ratios (0.25–0.35) were studied. Vertical loads of 400 N were applied on occlusal points, while the roots of the molar teeth, below the crevices, were supported in all directions. All the materials were modelled as homogeneous, isotropic, and elastic. The maximum principal stresses at the restoration-enamel junctions were strongly dependent on the MOD restoration geometries. Peak stresses occurred along the palatal surface of the restoration rather than the opposite buccal surface. Double-curved restorations showed the lowest peak stress at restoration-enamel junctions. Choice of the mechanical properties of restorative material in the range of 5–35 GPa further reduced stress concentrations on the enamel. Class II MOD restorations may be stronger if designed with double-curved marginal geometries that can reduce stress concentrations. Designs with convex and concave geometries were particularly effective because they reduced stress concentrations dramatically. Results suggest that relatively minor changes to the geometry of a restoration can have a substantial effect on stress at the restoration-enamel junction and motivate future experimental analysis.

Authors: Behzad Babaei, Paul Shouha, Victor Birman, Paul Farrar, Leon Prentice, Gangadhara Prusty
Year:��2021
Journal name: Journal of the Mechanical Behavior of Biomedical Materials

Abstract: A detailed analysis of the microstructure of five 3D printed CF/PEEK samples and the commercial feedstock material used to produce them has been conducted by the means of state-of-the-art micro-CT imaging. The images unequivocally show that both feedstock filament and printed samples contain a large quantity of voids heterogeneously distributed. Voids are randomly distributed within the feedstock, while they are aligned in rows parallel to the mould plate within the printed samples. Short fibers are heterogeneously distributed and display a preferential alignment in all specimens. Overall, the results showed that the 3D printing process did not remove the voids originally present in the feedstock filament and varying key printing parameters had only a minor effect on the printed samples’ void content, while the depositional nature of the printing process strongly affected the samples’ internal geometry.

Authors: S. Sommacal, A. Matschinski, K. Drechsler, and P. Compston
Year:��2021
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: This work investigates the effectiveness of fluorinated silica-based superhydrophobic coatings to protect 3D-printed carbon-fibre/polyamide composites against moisture-induced degradation. Increasing exposure time in wet and humid environments led to a reduction of tensile strength and an increase in experienced strain. However, the coated PA demonstrated 6.7–12.4% higher tensile yield strength than the uncoated PA. High-resolution X-ray micro computed tomography (μCT) was used to image the microstructure and revealed that the superhydrophobic coating effectively prevented liquid water penetration into 3D-printed polyamide and delayed water vapour-driven mechanical degradation. The presence of the superhydrophobic coating eliminated the liquid water presence in the surface features of the PA matrix and reduced the moisture-induced swelling of the polyamide matrix by about 53% after 168 h under water. Further optimisation of these coatings may provide a solution to enhance the performance of PA composites in humid and wet environments.

Authors: P.B. Kreider, A. Cardew-Hall, S. Sommacal, A. Chadwick, S. Hümbert, S. Nowotny, D. Nisbet, A. Tricoli, P. Compston
Year:��2021
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: This paper investigates the vibrational behaviour of smart orthotropic cross-ply laminated stepped beams. Specifically, an analytical closed-form model based on the first-order shear deformation theory (FSDT) is developed to consider a step change in laminate configuration along the beam axis due to integration of a piezoelectric patch for actuation applications. The 6th order governing equation within each element, along with appropriate continuity, equilibrium, and boundary equations, were formulated. State-space approach was utilised to find the beam's response to piezoelectric sinusoidal actuation. Results of the natural frequency analysis were compared with results in the literature and finite element modelling. An experimental investigation examined the accuracy of the analytical method to find the natural frequencies and forced vibrational response of a smart carbon-fibre/polyetheretherketone (PEEK) cantilever beam. Comparisons demonstrate that the provided closed-form method is capable of efficiently predicting the free and forced vibrational behaviour of smart stepped laminated composite beams with high accuracy.

Authors: S. Fazeli, C. Stokes-Griffin, J. Gilbert and P. Compston
Year:��2021
Journal name: Composites Part A: Applied Science and Manufacturing

Abstract: Carbon-fibre reinforced composites are seeing increased deployment, especially in the aerospace industry, and the next-generation of these materials will need to meet demanding performance requirements beyond just specific strength. The incorporation of nanomaterials such as graphene into composites has great potential for enhancing electrical, thermal, and mechanical properties, which could then enable new capabilities such as built-in lightning strike protection and electromagnetic shielding. One major challenge is successful integration of nanomaterials into the composite during the manufacturing process especially for thermoplastic based composites. This work explores the spray deposition of exfoliated graphene in liquid suspensions for the nano-enhancement of electrical properties in carbon-fibre reinforced polyether ether keytone (PEEK) composites. Developed thin films were smooth with RMS roughness of 1.06 μm on Si substrates and RMS roughness of 1.27 μm on CF-PEEK tapes. The addition of 1.3 wt% graphene into the interlayers of CF-PEEK composites resulted in bulk electrical conductivity enhancement both in plane and through thickness of ~ 1100% and 67.5% respectively. This approach allows for pre-consolidation introduction of high-performance nanomaterials directly to thermoplastic prepregs which could open simple pathways for the in-situ manufacturing of carbon-fibre reinforced polymer nanocomposites.

Authors: Christopher Leow, Peter B. Kreider, Christian Notthoff, Patrick Kluth, Antonio Tricoli and Paul Compston
Year:��2021
Journal name: Functional Composite Materials

Abstract: Automated fibre placement (AFP) technique has been progressively being adapted for high-quality fibre reinforced composite manufacturing for narrow tow placement, near-net shape output (low wastage) and reduced cycle times. Laser or hot-gas torch (HGT) is commonly used as the heating source in this process which has a significant influence on the quality of manufactured laminates. The capability of HGT-based AFP for manufacturing high-quality thermoplastic composite laminates and its parametric optimisation is investigated in this study. A series of AFP made coupon samples are manufactured using various processing parameters such as the deposition rate (60 mm/s-90 mm/s), consolidation force (180N-450N) and HGT/melting temperature (650-950 °C) to investigate on the processing parameters for optimisation. The interlaminar shear strength (ILSS) is evaluated for the samples using the short beam strength experiments on the manufactured samples using different parametric conditions. The influence of manufacturing processing parameters on the mechanical strength are discussed. Also, it is shown how the processing parameters will affect the overall quality of the laminate. The structural analysis confirmed a sandwich type layered structure in all coupons. However, the processing parameters influence on the resin-rich area within the laminate. Further, a sever fibre damage phenomenon observed in the sample manufactured at 450 N and 950 °C. Therefore, the mechanical strength and the specimen quality of laminates are critically dependent on the choice of manufacturing parameters and appropriate selection of them would provide optimal values.

Authors: Ebrahim Oromiehie, Asit Kumar Gain, B. Gangadhara Prusty
Year:��2021
Journal name: Composite Structures

Abstract: Fibre-reinforced dental composites are proven to have superior mechanical properties in comparison with micro/nano/hybrid filled composites. However, the addition of small quantities of short glass fibres could affect the dimensional stability of the restoration both during initial stages as well as through the life of the restoration. This in-vitro study aims at evaluating the physical properties of short S-Glass reinforced flowable dental composites. Two S-Glass short fibre-particulate reinforced (5 wt% of aspect ratios 50 and 70) and one particulate only reinforced flowable dental composites were prepared with UDMA-TEGDMA based dental monomer systems. Samples were photopolymersied for 60 s and stored in distilled water at 37 °C for 24 h before testing. Depth of cure (through-thickness microhardness), volumetric shrinkage (Archimedes technique), polymerisation stress (cantilever based tensometer), curing exotherm (thermocouple), water sorption and solubility (ISO 4049) and thermal expansion coefficient (dilatometer) were determined. The test results were statistically analysed using one-way ANOVA (p < 0.05). Depth of cure increased by 41%, volumetric shrinkage increased by 8.3%, shrinkage stress increased by 37.6%, exotherm increased by 20.2%, and thermal expansion reduced by 6.4% while water sorption and solubility had a negligible effect with the inclusion of short glass fibres. The study demonstrates that within the same organic resin system and quantity, a small replacement of fillers with short fibres could significantly affect the dimensional stability of the composite system. In conjunction with mechanical properties, this study could help clinicians to gain confidence in fibre reinforced dental composite restorative system.

Authors: Raju, Ginu Rajan, Paul Farrar and Gangadhara Prusty
Year:��2021
Journal name: Scientific Reports

Abstract: Manufacturing of thermoplastic composites using automated fibre placement (AFP) machine with specific characteristics is a challenging task due to the interdependence of various processing conditions and variables. It is of interest to know the accurate value of different input variables which would give the desired characteristics (outputs) of the laminates. This problem comes under the framework of inverse identification and is often ill-posed and its solution becomes increasingly difficult when the available data samples are very less. The present study develops a neural network-based inverse predictive model for AFP based manufacturing process using virtual sample generation (VSG) techniques. The efficacy of the developed predictive inverse model has been established considering varieties of experimental data. The proposed approach can be applied to a large class of manufacturing processes to determine the input conditions to a get product with desired characteristics.

Authors: Chathura Wanigasekara, Ebrahim Oromiehie, Akshya Swain, Gangadhara Prusty & Sing Kiong Nguang
Year:��2021
Journal name: Journal of Industrial Information