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Engineering structures are often subjected to fluctuating loads, which onset materials' fatigue and deleteriously affect their service life. This becomes crucial for fiber reinforced polymer (FRP) composite structures because their fatigue response is different from metals, complex, and can lead to catastrophic consequences. The desire and need to improve fatigue performance have been progressive and have led to the use of fillers as secondary reinforcement in matrix. In fact, ceramic, carbonaceous, clay, and polymer fillers have been extensively studied to enhance mechanical performance, but very limited study is available on the fatigue performance of FRP composites modified with fillers. Therefore, this work includes an extensive review on the use of fillers reinforcement to improve the fatigue performance of FRP composites, especially with thermoset and thermoplastic matrices. The various fatigue improvement mechanisms contributed by fillers are identified and explained. A comparison is made among the available literature to map the enhancement in the fatigue life of carbon and glass reinforced composites and the filler content used therein. This review shows that carbonaceous and polymer fillers have a positive reinforcing effect and provide maximum improvement in fatigue life by a factor of 11 and 100, respectively. There is enough evidence that the addition of fillers enhances the fatigue strength of thermosets composites, whereas not enough data is available yet to understand the fatigue performance of thermoplastic composites with fillers in entirety. In the end, the future potential and the likely challenges are summarized and discussed.

Current research investigates the effect of the core-shell (C/SH) particles in composites manufactured using novel thermoplastic Elium® resin and carbon fiber reinforcement of different areal weights, 200 gsm and 400 gsm bi-angle non-crimp carbon fabrics (NCCFs). The core-shell particles were activated using the ex-situ methodology which involves the activation of particles before the Resin transfer molding (RTM) injection process. Recommended particle activation parameters are established after carrying out a detailed microscopic study to understand the melting and flattening behavior of these particles. Static indentation and damping attributes are studied to understand the influence of C/SH particles added novel carbon/Elium® composite in improving the out-of plane properties and dynamic mechanical attributes respectively. The interply regions were also toughened with the addition of 1% core-shell particles and the intensity of load drop has reduced by 20% while comparing the thick and thin ply NCCF/Elium® composites. Microscopic examination has shown that the core-shell particles helped to spread the damage evenly throughout the specimen and absorbed more energy during the static-indentation. Loss factor or damping for thick ply Elium® composite and thin ply epoxy composite is increased by 19% and 16.4% with the addition of 5% and 1% C/SH particles respectively. The underlying reasons for improvement offered by C/SH particles in quasi-static impact and dynamic mechanical tests are also deliberated in this paper.

The load response, energy absorption, different damage mechanisms and failure modes of sandwich panels subjected to complete perforation by quasi-static indentation and the insights gleaned are presented in this paper. The experimental campaign was carried out on samples made of different type of facesheets: Aluminium, glass fibre-reinforced plastic and metal-composite hybrid (combined aluminium and GFRP) with two different core heights. Reliable numerical models were developed with appropriate constitutive material and damage model for facesheets and honeycomb core to complement the experimental observations. Good agreement between experimental results and numerical predictions in terms of force-displacement response and perforation damage ensure the fidelity of the developed numerical model. Effects of facesheet type, core height, energy absorbed by the constituent layers, damage evolution history are briefly discussed. It was observed that the energy absorption of sandwich panels and peak indentation force resisted by the top and bottom facesheet are strongly dependent on its metal-volume fraction, whilst unaffected with the height of the core. Recommendations for developing computationally efficient numerical models were provided.

Machine Learning (ML) is useful in predictive analytic or prognostic modeling for materials and engineering. It is, however, challenging to gather sufficient and representative data. Experiments are possible only in small numbers due to specialty materials, manufacturing, infrastructure, and testing involved. Simulation and numerical models need skills and appropriate validation. If the dataset at hand is too small in size to train ML, professionals tend to create synthetic data, which may not necessarily meet the quality required of the new data. A Knowledge-based Data Boosting (KDB) process, named COMPOSITES, that rationally addresses data sparsity without losing data quality is systematically discussed in this paper. A study on inter-ply fracture toughness of carbon nanotube (CNT) engineered carbon fibre reinforced polymer (CFRP) composite laminates is used to demonstrate the KDB process. This involved strengthening of inter-ply interfaces using CNT advocated for improving delamination resistance of the CFRP composites. It is demonstrated that the KDB process helped augment the dataset reliably and improved the best fit regression lines. The process also made it possible to define boundaries and limitations of the augmented dataset. Such sanitised dataset is certainly valuable for prognostic modeling. Accepted version

The porous interconnected structure of three-dimensional graphene (3DC) combines the excellent thermal conductivity of graphene with an interconnected architecture, thereby creating a thermal network within composites infused with 3DC. In this study, improvements in thermal conductivity, latent heat of fusion (Hf) and shape-stability of paraffin were compared between paraffin phase change materials (PCM) infused with 3DC and with discrete graphene flakes (GP) at the same filler loading to quantify the advantage of the interconnected structure. Paraffin infused with a 3DC of higher bulk density (3DCH) was also compared to identify the effects of increasing filler density. Thermal conductivity of the PCM composites was measured using the hot-disk method and shape-stabilization was compared through thermal cycling in an environment chamber. We found that the interconnected architecture of 3DC improved the properties of the paraffin matrix in multiple ways. 3DC improved the solidification process for paraffin with heterogeneous nucleation, helped to retain the shape of the PCM composite over thermal cycling, reduced void formation within the PCM and induced a large increase in thermal conductivity at 7.4 times and 5.2 times that of neat paraffin for composites infused with 3DCH and regular 3DC respectively, with only a small trade-off in Hf. EDB (Economic Devt. Board, S’pore) Accepted version

The bladder molding process is primarily used in sporting applications but mostly with prepregs. Bladder-Assisted Resin Transfer Molding (B-RTM) presents the tremendous potential to automate and mass produce the complex hollow-composite profiles. Thin-ply, non-crimp fabrics (NCFs) provide excellent mechanical, fracture toughness, and vibration damping properties on top of the weight saving it offers to a final product. However, these fiber architectures are difficult to inject due to the resistance they provide for the polymer flow using the liquid injection process. Therefore, it is mandatory to optimize the process parameters to reduce the time for injection and simultaneously achieve better consolidation. This work presents a first, detailed, experimental case study to successfully inject a low-permeability, thin-ply, complex, thermoplastic tubular structure, and the effect of process parameters, boundary conditions, the associated manufacturing challenges, and proposed solutions are deliberated in this paper.

Carbon composites are deemed suitable for components with complex geometries which require high impact resistance. The broad range of industrial applications requires composite structures to be lighter and not to compromise with their mechanical performance. Non-crimp fabrics with lower fibre areal weight (FAW) are the class of reinforcement material which will only bring the advantages of better mechanical properties but will also offer more longevity to the structures and reduced maintenance costs. This research aims at investigating the low-velocity impact performance of textile spread tow thin ply (100 gsm) composites with an aim to study the load bearing capability, deflection characteristics and energy characteristics. The results are compared with the baseline thick (200 gsm) fibre reinforced composites. There was 19.2 %, 16.6 %, and 6.57 % higher peak load for spread tow thin ply composites when compared to thick ply composites at 25 J., 42 J., and 52 J impact energies respectively. Significantly lower residual deflection (40 % to 76 %) and higher major damage energy (20 % to 33 %) were observed for spread tow thin ply laminates compared to the thick ply variant at different impact energies. At 42 J and 52 J impact energies, the damage index (DI) was 2 times and 4 times higher for Thick ply laminates highlighting extensive damage, which is also observed with detailed failure mechanisms study.

Fiber-reinforced polymer composites, such as carbon-epoxy composites, are found to exhibit non-linear behavior when mechanically loaded in the transverse and shear directions. Experimental studies suggest that the non-linear behavior is due to two mechanisms: (i) damage in the matrix in the form of cracks and (ii) yielding of the matrix followed by plastic deformation. In this study, a bimodulus-plastic model that includes these two different damage mechanisms to simulate the non-linearity prior to failure is proposed. The pre-failure, onset of failure and post-failure analysis with the proposed model is discussed in detail with emphasis put on the transverse and shear components. The process of determining the material properties and parameters required for defining the new model is discussed and demonstrated. The newly developed model is then validated against the experimental results from three-point flexure tests on the composites. The correlation was good showing that the proposed model was able to simulate accurately the non-linear behavior of the composites and thus predict the failure. Finally, the model is applied to a case study on the failure of a composite riser under internal pressure loads. Accepted version

Textile non-crimp carbon fabrics (NCCFs) are made of several dry uni-directional (UD) tows which are aligned straight and stitched together. The use of these reduces resin rich areas and stress concentrations that are likely found in woven fabrics composites during manufacturing. The use of spread tows to manufacture the thin plies leads to the fibre areal weight (FAW) of lower than 150 g/m2. This current research aims at investigating the tensile, flexure and interlaminar shear response of thin ply carbon composites with a view to deduce the failure mechanisms. The baseline comparison is carried out with conventional thick ply composites and differences in the failure mechanisms are studied. For tensile tests, reduced number of acoustic emission counts in the case of thin ply composites indicated that the stresses were unaffected until the laminate ultimate strength. In flexural tests, it was noticed that the resin rich sites near the stitches first initiated compression failure followed by translaminar cracking or longitudinal fibre fracture. This is due to the strong fibre-matrix adhesion in the case of thin ply composites. No interlaminar shear fracture was seen to occur throughout the laminate thickness and across the width, leading to a significant improvement in the flexural properties of the thin ply composites. These thin laminates have better interlaminar shear properties. It was observed through microscopy that thin ply laminates first undergo interlaminar shear followed by inelastic deformation at the ultimate strength of the material.

This study presents the design and analysis of the segmented rotor design for an electrical machine embedded onto the more electric aircraft gas turbine engine shaft. The high-speed operational environment imposes high stress levels due to centrifugal forces; thus, the feasibility of this segmented rotor topology for such application is explored and a suitable design is proposed to overcome mechanical stresses. Finite element structural analysis was performed to compare the mechanical behaviour of a different rotor segment fixing structure and the proposed design. Also, electromagnetic analysis is carried out on a high-speed switched reluctance machine to study the impact of a new design on machine electromagnetic performance. NRF (Natl Research Foundation, S’pore) Published version

Fiber reinforced thermoplastic composites are gaining popularity in many industries due to their short consolidation cycles, among other advantages over thermoset-based composites. Computer aided manufacturing processes, such as filament winding and automated fiber placement, have been used conventionally for thermoset-based composites. The automated processes can be adapted to include in situ consolidation for the fabrication of thermoplastic-based composites. In this paper, a detailed literature review on the factors affecting the in situ consolidation process is presented. The models used to study the various aspects of the in situ consolidation process are discussed. The processing parameters that gave good consolidation results in past studies are compiled and highlighted. The parameters can be used as reference points for future studies to further improve the automated manufacturing processes.

Nowadays, laminated composites are widely used in the aerospace sector. All laminates have interply/interlaminar interfaces even if they are made using automated processes. The interfaces act as the areas of weaknesses and the potential crack initiation regions. Hence, any enhancement in the crack initiation and propagation resistance is always sought after. Usage of polymeric thin films is one of the promising and viable ways to achieve this. It is also easy to incorporate micro-thin films into any automation process. In the present study, different customized thin films that are compatible with Glass/BMI composites are fabricated. Fracture toughness tests in Mode I (opening mode), Mode II (sliding mode) and Mixed Mode I/II are conducted respectively using Double Cantilever Beam (DCB), End Notch Flexure (ENF) and Mixed Mode Bending (MMB) test specimens. This paper discusses the manufacturing of compatible micro-thin films. The various challenges faced during the manufacturing and incorporation of thin films are presented. The results of the various fracture toughness tests are examined. Mechanisms through which the different films help in resisting the crack initiation and propagation are deliberated and discussed. The incorporation of this technique in Automated Fiber Placement (AFP) is also discussed.

One of the main downsides of fiber reinforced polymer composite laminates is their susceptibility to impact damage. Many different methods have been devised to either modify or engineer the composites to improve their impact resistance and tolerance. In this chapter, three types of engineered composites and their impact performances are presented and discussed. The engineered composites are (i) composites with core–shell polymer particles, (ii) composites with carbon nanotubes/nanofibers and (iii) composites with thermoplastic film interleaves. Core–shell polymer particles absorb large amounts of energy during impact, thus limit the damage done to the composite laminate. Carbon nanotubes and nanofibers have excellent stiffness and strength, making them suitable for reinforcing the interlaminar regions of composite laminates, leading to improved impact resistance. For composites with thermoplastic film interleaves, thermoplastic films with high intrinsic toughness modify the interlaminar regions of the composite laminate and enhance the overall toughness. The three types of engineered composites exhibit varying levels of improved impact performances compared to the unmodified composites. For each type of engineered composite, its impact response, the strengthening mechanisms and factors affecting its impact performance are deliberated.

This chapter describes the methods and material used to produce carbon nanotubes (CNTs)-reinforced multiscale composites. It also includes material selection, manufacturing process, and specimen preparation. Dry CNTs transfer technique is the primary approach adopted here to manufacture the CNT-based multiscale composites. This chapter is concerned with the experimental work carried out to determine the influence of CNTs on the interlaminar fracture toughness (ILFT) of the woven carbon fiber reinforced plastic (CFRP) prepreg laminates. The mode-I and mode-II studies were performed to quantify the ILFT for present material system. A detailed quantitative analysis of fiber bridging and CNTs effect on ILFT was executed. Based on ILFT test results, the fiber bridging and CNTs effect on ILFT were calculated.

The contributions made by multiwall carbon nanotubes and the fiber bridging to the improved interlaminar fracture toughness (ILFT) of the carbon fiber-reinforced plastic laminates were verified by morphological analysis. Interlaminar fracture (ILF) morphology was needed to distinguish the fiber bridging and carbon nanotubes strengthening effect. For the morphological study, the test samples were examined during ongoing testing (in situ) to understand fiber bridging and the other causes that improved the ILFT. After testing, laminates were split open, and the ILF surfaces were examined by microscope and field emission scanning electron microscope/scanning electron microscope (FESEM/SEM) to look at the various interlaminar mechanisms that improved the ILFT. The step-by-step process of ILF morphology for multiscale interlaminar interface is demonstrated in detail. All the findings are discussed with the help of the test data, FESEM images, and the images of the ILF surfaces.

A potential application of this multiscale composites and the methodology is validated by modeling a double cantilever beam specimen using finite element methods and analyzed. Mori–Tanaka micromechanics was used to evolve the bulk properties of the carbon nanotube (CNT)/epoxy nanocomposite. An existing analysis strategy was employed that used cohesive elements to model the toughness effects on the delamination initiation as well as propagation. The cohesive element model was derived from superposition of two cohesive laws—one accounting the fiber bridging effect and the matrix strengthening by CNTs and the other representing the initiation of the interlaminar fracture toughness (ILF). The numerical simulation correlated well with the experimental results. The present study involves analytical investigation of the mode-I ILF and addresses the overall toughening effects due to CNTs and fibers.

Non-crimp fabrics are fabric tapes stitched to an adjacent orthogonal fabric with no associated crimp. In the current research, the effect of fixation polyester stitches in improving through-the-thickness properties of non-crimp fabric composite laminates is investigated. Detailed experimental studies on interlaminar fracture toughness and static indentation properties of stitched and unstitched thin ply carbon fibre epoxy composites have been conducted. About 23% higher peak load and 37% higher energy absorption were noticed during static indentation tests for the stitched ply composites. A detailed SEM investigation has shown that the stitch-stitch interaction ‘within a bi-angle ply’ and ‘between the bi-angle ply’ plays a significant role in reducing the delamination extent. The critical energy release rate during Mode I fracture toughness of stitched composites was found to be 26.5% higher and SEM investigation depicted that the stitches promote the intra-laminar delamination and enhance the toughness of the composite. Nanyang Technological University The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors would like to acknowledge the financial support from Institute for Sports Research, Nanyang Technological University, Singapore and CHOMARAT, France and ARKEMA, France.

Laminated polymer composites are extensively used in various applications ranging from aerospace to automotive, building to marine and offshore, and much more. These composites possess higher mechanical properties in their in-plane directions, but lower interlaminar properties. Especially, low interlaminar fracture toughness (ILFT) makes them susceptible to delamination. In the current research, a novel thermoplastic-based thin-ply composite system is conceptualized and manufactured with an aim to improve the through-the-thickness properties and which can be a competitive solution to traditional epoxy-based composites as well as other class of thermoplastic composites. The detailed experimental investigation on determining the Mode I ILFT properties of these thin ply carbon fibre thermoplastic composites, along with thin ply thermoset composites for benchmarking, is carried out. Quasi-isotropic composite laminates were manufactured using a room temperature cure epoxy, and the novel reactive Methylmethacrylate (MMA) liquid thermoplastic resin. The thin ply/liquid MMA composites have shown 30% and 72% higher Mode I ILFT properties compared to the thick ply/liquid MMA and thin ply/Epoxy composites respectively. Surface morphological studies were conducted to understand and differentiate damage mechanisms in these composites. From the comprehended damage mechanisms, it was deduced that strong fibre-matrix interface, plastic deformation as well as features like ductile drawings in liquid MMA composites make them more resistant to crack propagation.

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90),(45/−45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (−0.1 &amp, −0.5) and two frequencies (3 Hz &amp, 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young’s moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible.

This paper presents the details of vibration damping enhancement offered by the composites made up of thick and thin plies of carbon fibres with a novel liquid Methylmethacrylate (MMA) thermoplastic resin possessing characteristics similar to thermoset resin. After developing the novel composite system, its damping attributes are studied and a baseline comparison is carried out with a carbon fibres/epoxy resin composite system. The liquid MMA was found to be 27% more efficient in improving the structural damping compared to the epoxy resin. The increase in the dynamic loss modulus and loss factor calculated from the dynamic mechanical analysis (DMA) tests confirmed the positive influence of the reactive liquid MMA resin and the thin plies in dampening the vibrations. The vibration tests carried out indicated an increase in the damping ratio with the decrease in the individual ply thickness. The damping capacity at room temperature and at the glass transition temperature of carbon fibre/liquid MMA composites was found respectively 13% and 74% higher than the carbon/epoxy composite system. The details of the vibration and DMA tests conducted along with the rationale and underlying reasons for the accomplished advantages of the thin plies and liquid MMA resin composites system in vibration damping are presented.

This paper presents a multi-scale progressive damage modeling strategy to investigate the damage and failure behaviors of 2D woven composites. The micro-scale and meso-scale RVEs are identified to sequentially consider the fiber/matrix scale and the tow architecture scale. The micromechanics failure criterion is then introduced to facilitate analysis of the damage initiation and evolution at the constituent level. An anisotropic damage model is also constructed based on the Murakami-Ohno damage tensor, and the damage evolution is governed by the material fracture energy during failure. The proposed multi-scale strategy is carried out by a user-material subroutine (UMAT) in ABAQUS, which predicts the detailed local responses and complex failure mechanisms of the woven composites. Moreover, experimental tensile and compressive tests are conducted to further validate the proposed model.

Electrically nonconductive composites are required in various engineering applications ranging from radome, antenna and many more. This research aims at investigating the mechanical properties of electrically non-conductive hybrid composites (thin carbon non-crimp fabric, Kevlar and E-glass fabrics) in combination with thermosetting epoxy resin. The composites comprise of multi-axial textile reinforcement carbon fabrics in the middle section with symmetrical quasi-isotropic layup, sandwiched with Kevlar fibre for improved impact performance and E-glass fibre at the outermost parts for electrical insulation. The fabrics are injected with room-temperature-cure epoxy using economical and energy saving resin transfer moulding manufacturing process. Electrical continuity tests and mechanical properties including vibration damping response, flexure and impact were studied to investigate the performances of the manufactured hybrid composites. Three hybrid laminate configurations were manufactured, and experimental results showed that hybrid composite with more number of Kevlar layers performed better for vibration and flexure testing. For impact performance, results showed that the absorbed impact energy improved with the inclusion of more glass layers, whereas configuration with more Kevlar layers experienced greater peak load to failure. The details of the composites fabrication, manufacturing and experiments conducted and the related findings with underlying reasons for the improvement offered by particular group of laminate configuration are discussed in the article.

A scaled, 7.5-mm thick, unidirectional glass/epoxy wind turbine spar cap cured in a vacuum-assisted oven was found to have attained non-uniform thickness along its length. Edge deformations were severe, leading to noticeable edge curvature even at the vacuum pressure. These unforeseen discrepancies could only be predicted and/or dealt beforehand through a process simulation that integrates the complete processing physics. A fully coupled numerical simulation of composites manufacturing was established and implemented for a portion of a spar cap in multiphysics finite element software. Phenomena such as resin flow-induced compaction and cure-induced deformation were captured. The simulation results indicated that even though the distorted edge of the laminate is trimmed off, there will still be some curvature left within the part. It was noted that simulating percolation flow of resin alone leads to less accurate deformation predictions. Therefore, a method to include shear flow-induced deformation of the resin-saturated fiber beds were proposed and implemented. Such a fully coupled and integrated procedure is useful for optimizing process parameters to achieve intended final part with accurate dimensions and minimal manufacturing-induced defects or deformities.

Even with small infinitesimal increase in load, change of equilibrium configuration of completely different character is highly possible for thin shell structures and that could eventually result the whole structure become unstable. This article presents numerical investigation on buckling and post-buckling characteristics of laminated composite circular cylindrical/conical shell subjected to torsional, thermal and combined loads. Using commercial finite element software ABAQUS, both linear and non-linear buckling response of composite shells are simulated. Linear critical buckling load due to uncoupled torsional and thermal loads is determined using eigen value buckling analysis. Non-linear post-buckling response of shell is simulated using Riks arc length method. Un-coupled and coupled influence of thermal-torsional influence to critical buckling load is estimated. Mode shape associated with linear Eigen value analysis are used as initial geometric imperfection for non-linear analysis. Thermo-mechanical coupling found reduces the buckling load resistance of cylindrical shell by maximum of 47%. It was observed that the generation of additional axial compressive reaction force due to thermal expansion restrain on axial constrained shell edges could be the major influential factor. Except a small radial expansion of cylindrical surface, deformation shape predicted from non-linear post buckling analysis resembles rather similar irrespective of any proportion of thermal-torsional coupling.

Reactive thermoplastic matrices are widely used for polymer composites manufacturing owing to their ease of processing using cost-effective liquid injection processes. The novel methyl methacrylate (MMA) Elium ® resin is a liquid thermoplastic resin, first of its kind which is curable at room temperature. It has attracted wide interest as a competitive solution to epoxy-based composites for structural applications. In this work, the flexural performances of novel non-crimp carbon fabric (NCCF) Elium ® composite laminates are evaluated. The baseline comparison is done with conventionally used composites with epoxy resin. The stress-strain curve, the fracture failure mechanisms and the effect of the annealing stage have been discussed. Nanyang Technological University Authors would like to acknowledge the financial support from the Institute for Sports Research, Nanyang Technological University, Singapore, Arkema, France and CHOMARAT, France.

Resin pressure distribution of a curing Glass/Epoxy prepreg lay-up is the key parameter that controls the strength, stiffness and void nucleation of the cured composite part. It is vital to monitor and control the resin movement of curing laminate to optimize its quality in any manufacturing process. In this paper, design of a Fiber Bragg grating (FBG) based device, capable of measuring in-situ resin pressure of a curing lay-up is presented. This device uses the principle of differential pressure in liquids. The device was calibrated using a water column, and a pressure sensitivity of 1.636 × 10 −2 MPa −1 was yielded. FBG responds linearly with the rise of hydrostatic pressure in the water column. An excellent agreement was found between experimental and theoretical results. This device was used to monitor the resin pressure in a curing prepreg composite lay-up. The measured liquid resin pressures were also compared to the resin pressure obtained from a coupled multi-physics numerical simulation. The presented sensor is useful for in-situ pressure measurements, especially for high temperature and low or zero bleed curing of composites, for example, out of autoclave curing.

A novel technique to predict the manufacturing process-induced distortions and deformations in thick unidirectional carbon fiber reinforced plastics laminates is detailed in this article. An integrated numerical model is developed to account for non-isothermal resin flow, related compaction, transient resin cure, and resin shrinkage effects to predict the final shape of the autoclave cured thick prepreg laminate. The associated physics are mathematically coupled to solve for the process variables interactively. The results illustrate reduction in the thickness of the laminate prior to the start of curing when initial fiber volume fractions are pre-set. This confirms that the initial transverse deformation of B-stage prepreg is due to the applied vacuum and/or pressure. Once curing initiates, deformation of the laminate due to compaction increases, proportionally, with the increase in fiber volume fraction. Furthermore, the thermo-chemical residual strains contribute to additional compaction. The final distorted shape observed in simulation of the originally flat laminate matches with the shape of the fabricated laminate with 6.6 mm thickness. A solution to minimize the distortion is discussed in detail. This procedure is extended to simulate a curved laminate’s processing; where, the shear moduli were observed to influence the final shape of the laminate. The findings are presented and deliberated in this article.

Braided textile composite exhibits an efficient mechanism to distribute loads throughout its structure and have excellent impact resistant properties. Despite many works in the past, the successful prediction of braided textile composites strength still remains a challenge today. In this paper, a numerical simulation model based on a meso-scale approach is presented to predict the strength and damage behavior of braided textile composites. A meso-scale homogenized representative unit cell was built for the study using finite element analysis (FEA) method. 3D-Hashin and Stassi failure criteria were respectively selected for the yarn and the pure matrix, and coded in a subroutine in Abaqus finite element solver to study the individual constituents damages. From the different numerical studies, the failure mechanisms were observed to change with the braiding angle. The meso-scale computed results were also seen to agree closely with experimental and simulation results computed using a micro-mechanics failure approach.

This paper presents the analysis of different soft magnetic materials for high-speed, high-temperature applications, such as embedded electrical machines for aircraft gas turbine. The aim is to provide a comparison of their electromagnetic and thermal impacts, for varying alloy content and lamination thickness. The comparative study is carried out among different lamination material choices based on iron loss, thermal impact, and power density using a finite element analysis tool. Through this simulation study, cobalt-iron alloys appear to be the optimum choice for their combination of high thermal capability with high strength and high saturation magnetization. Furthermore, it is suggested that alloys with thin laminations will limit high iron losses.

A novel composite scarf joint is successfully fabricated with thermoplastic core shell microparticles incorporated into the interlaminar interface regions with a dual objective of mitigating the impact damage and improving the stiffness compatibility of the joint. The impact analysis of the joints revealed that the incorporation of microparticles led to a significant improvement of the impact load bearing capacity of joint and reduced the extent of the damage area. It is also observed from flexural tests that the microparticles reduces the stiffness of the laminate proportional to the weight fraction of the particles and thereby help design a joint adherend with controlled matching stiffness. This engineered scarf joint adherend configuration has the potential to minimise stiffness mismatch between a fatigue worn-out damaged composite part and the new scarf repair patch laminate designed for it. This shall help ensuring an easy restoration of uniform load distribution in the newly bonded composite scarf j...

A manufacturing technique was successfully adopted for incorporating core–shell polymer (CSP) particles into glass fiber reinforced polymer (GFRP) composites. CSP particles were firstly added into inter-ply interfaces during the lamination process. Conventional as well as CSP particle filled GFRP laminates were then cured at 122 °C under high pressure while in a vacuum environment. Good adhesion between the particles and the epoxy matrix was achieved during the curing. GFRP laminates with or without particles were immersed in water at 80 °C for different durations. These conditioned laminates were later subjected to low-velocity impact tests. It was found that the GFRP laminates with CSP particles absorbed more moisture while had less structural defects formed during the conditioning. The CSP particles significantly improved the impact properties of the GFRP laminates. After hygrothermal aging, the beneficial effects brought about by these particles for effectively resisting impact loads diminished. The underlying mechanisms were identified, studied and explained. Keywords: GFRP, Composites, Core–shell polymer particle, Hygrothermal, Impact, Tensile

This study details a fabrication methodology envisaged to manufacture Glass/BMI honeycomb core aerogel-filled sandwich panels. Silica aerogel granules are used as core fillers to provide thermal insulation properties with little weight increase. Experimental heat transfer studies are conducted on these panels to study the temperature distribution between their two surfaces. Numerical studies are also carried out to validate the results. Despite exhibiting good thermal shielding capabilities, the Glass/BMI sandwich panels are found to oxidise at 180 ºC if exposed directly to heat. In order to increase the temperature bearing capacity and the operating temperature range for these panels, a way of coating them from outside with high temperature spray paint was tried. With a silicone-based coating, the temperature sustainability of these sandwich panels is found to increase to 350 ºC. This proved the effectiveness of the formed manufacturing process, selected high temperature coating, the coating method as well as the envisaged sandwich panel concept. Published version

The current research presents a first attempt to manufacture thermoplastic tubular composites using carbon fibre as reinforcement and an innovative Elium® resin as the matrix material using Bladder Assisted Resin Transfer Moulding (B-RTM) manufacturing process. The manufacturing process parameters required to achieve a fully impregnated thermoplastic composites were established, and the parts have undergone impact, flexure, and vibration damping tests. The mechanical properties and the failure modes are compared with the tubes manufactured with conventional epoxy matrix. During impact testing, thermoplastic tubular composites have shown 16.3% and 18.9% higher peak load and major damage energy respectively compared to carbon/epoxy tubes. They have also shown distinctive failure modes, with acrylic Elium® composites tubes undergoing more ductile and spreaded failure whilst epoxy composites have shown brittle and catastrophic failure. Flexural tests have shown comparable load-carrying capability, higher strain to failure, and less delamination for carbon/Elium® composites compared to carbon/epoxy composites. These are attributed to the presence of microductlilty and other associated matrix deformation features shown during the fractographic analysis of carbon/Elium® composites. Vibration modal analysis tests have shown 21.7% higher structural damping for carbon/Elium® composite measured at different output locations on the tube. The differences in the failure mechanisms and the underlying reasons for the improvement shown by thermoplastic Elium® composite tubes under different mechanical tests are deliberated in this paper.

In order to build predictive analytic for engineering materials, large data is required for machine learning (ML). Gathering such a data can be demanding due to the challenges involved in producing specialty specimen and conducting ample experiments. Additionally, numerical simulations require efforts. Smaller datasets are still viable, however, they need to be boosted systematically for ML. A newly developed, knowledge-based data boosting (KBDB) process, named COMPOSITES, helps in logically enhancing the dataset size without further experimentation or detailed simulation. This process and its successful usage are discussed in this paper, using a combination of mode-I and mode-II inter-ply fracture toughness (IPFT) data on carbon nanotube (CNT) engineered carbon fiber reinforced polymer (CFRP) composites. The amount of CNT added to strengthen the mid-ply interface of CFRP vs the improvement in IPFT is studied. A simpler way of combining mode-I and mode-II values of IPFT to predict delamination resistance is presented. Every step of the 10-step KBDB process, its significance and implementation are explained and the results presented. The KBDB helped in not only adding a number of data points reliably, but also in finding boundaries and limitations of the augmented dataset. Such an authentically boosted dataset is vital for successful ML. Published version

Microwave curing has a tremendous potential to be used as an alternative to other thermal curing processes due to its shorter curing time and lower consumption of energy. Current research investigates the damping and dynamic mechanical characteristics of core-shell polymer (C/SH) particle modified glass fibre prepreg (GFRP) manufactured using microwave irradiations. The addition of C/SH particles has shown a significant improvement in damping and dynamic mechanical properties. The optimal areal weight per interface (AWI) for C/SH particles was established as 40 gsm. With this optimal addition, the laminates showed a 21.5% increase in mechanical loss factor, tan δ, and 52.7% in the vibration damping capability as noticed from dynamic mechanical and the forced vibration tests respectively. The underlying reasons for the improvement in properties with the addition of C/SH particles are also deliberated in this paper.

In the current research, the static indentation properties of composite laminates toughened by the addition of core-shell (C/SH) particles at the interfaces of non-crimp carbon fibre (NCCF)/Elium® composite laminate is investigated. NCCF/Elium® composite exhibited improved static indentation performance with an increase in the feed rate. There is a 19.6% and 13.5% increase in peak load with no particle reinforcement and 5% C/SH respectively when the feed rate was increased from 1 mm/min to 10 mm/min. Also, the 27% drop in the intensity of the major load drop was noticed when the interply region was toughened by the addition of 5% of the C/SH particles. Microscopic observations also showed reduced delamination with the increase of C/SH particles. The progressive failure was reduced due to increased energy absorption and delayed onset of fibre breakage and delamination.

Advanced manufacturing techniques, such as automated fiber placement and additive manufacturing enables the fabrication of fiber-reinforced polymer composite components with customized material and structural configurations. In order to take advantage of this customizability, the design process for fiber-reinforced polymer composite components needs to be improved. Machine learning methods have been identified as potential techniques capable of handling the complexity of the design problem. In this review, the applications of machine learning methods in various aspects of structural component design are discussed. They include studies on microstructure-based material design, applications of machine learning models in stress analysis, and topology optimization of fiber-reinforced polymer composites. A design automation framework for performance-optimized fiber-reinforced polymer composite components is also proposed. The proposed framework aims to provide a comprehensive and efficient approach for the design and optimization of fiber-reinforced polymer composite components. The challenges in building the models required for the proposed framework are also discussed briefly.

Interlaminar fracture or delamination is one of the major failure modes for fiber reinforced polymer (FRP) and fiber metal laminate (FML) composites. Many studies have been carried out to investigate the mechanisms affecting this interlaminar failure and ways to improve the interlaminar fracture toughness (ILFT) of FRP composites and FMLs. However, information on the topic is scattered, with studies having different emphases. Therefore, in this review, the studies are surveyed and put into perspective in terms of the improvements to ILFT achieved. A wide range of methods to improve the ILFT of FRP composites and FMLs is presented. For FRP composites, the methods include modifications to the constituents or interlaminar regions of the composite, applications of nano-fillers in multiscale composites approaches, and through thickness reinforcement techniques. For FMLs, studies on various surface treatment methods for the metal in FMLs are included. The strengthening mechanisms involved in each of the methods are also discussed. This review provides a comprehensive picture of the different methods to improve interlaminar interfaces in laminated composites, including their performances and drawbacks, as well as the future trends in the related topics.

The bonding between metal and carbon fiber-reinforced polymer (CFRP) composites is important in structures such as composite risers. Surface treatment of the metal is required to improve the metal-composite bonding. In this study, the effects of two mechanical surface treatment methods on the bonding between carbon/epoxy composites and aluminum are studied. The treatment methods investigated are grit blasting and grooving. Mechanical tests are performed and the test results are used with finite element simulations to study the failure and damage mechanisms at the composite-metal interface. The mechanical response and damage propagation at the metal-composite interface are modeled successfully using surface-based cohesive behavior. The finite element simulations gave insight into the way that the grooving treatment method improved the composite-metal bonding.

Experimental investigations were carried out to determine the low-velocity impact behaviour of carbon fibre composites with novel liquid Methylmethacrylate (MMA) thermoplastic matrix, Elium®. The load, deflection and the energy attributes under impact are studied in detail and the baseline comparison is carried with the carbon fibre composites with epoxy matrix . The quasi-isotropic non-crimp carbon fabric (NCCF) laminates were impacted at 25 J, 42 J and 52 J impact energies and the material response of both the composite configurations were studied. The composite laminates have shown less catastrophic damage at a high energy level (52 J) and around 10% higher peak load was observed. Structural integrity as measured from the load-deflection curve demonstrated up to 53% increase for Thin NCCF Elium composite compared to their counterpart composites with epoxy matrix. Significant energy absorption (56%) before the onset of major failure mostly through elastic-plastic deformations was observed for thin NCCF Elium® composite. Impact results at different energies showed the strain sensitivity of Elium® microstructure with the improved performance with increasing impact energy. From the detailed fracture and damage analysis of the impacted samples, the failure mechanisms were deduced for the novel Thin NCCF Elium® and epoxy composites .

An experimental investigation focusing on the hygrothermal aging-structural degradation–mechanical property relationship of GLARE 4A laminates was conducted. Water immersion conditioning at 80 °C for up to 4 months was carried out on GLARE 4A laminates. It was found that although the outer aluminum layers effectively protected the glass/epoxy composite layers from hygrothermal attack, the composite layers absorbed moisture through the edges. Consequently, significant decrease in both, the tensile strength and fatigue life of the GLARE 4A laminates, was observed although no structural defects were apparently identifiable in the microstructures of the conditioned laminates. Detailed experimental investigation was conducted to study the mechanism of mechanical property decay due to hygrothermal aging. It is proposed that the strength of the S2-glass fibers was not fully realized due to the weakening of the fiber/matrix interface and the deterioration of the sizing, which consequently led to the reduction in the tensile strength and fatigue life of the GLARE 4A laminates. The stiffness degradation characteristics of GLARE 4A laminates under cyclic loading were also investigated. Keywords: Fiber metal laminates, GLARE, Glass fiber, Hygrothermal, Tensile, Fatigue

The coupled nature of chemical kinetics, mechanical and rheological behavior of a curing prepreg dictates the dimensional accuracy of a composite laminate. In this work, an integrated study was carried out to understand the influence of thermo-chemo-mechanical and thermo-chemo-viscous effect on the curing strain of an epoxy laminate. The chemical kinetics of the resin was obtained from differential scanning calorimeter. The “instantaneous elastic modulus” was measured by using dynamic mechanical analyzer. An empirical model as a function of temperature and degree of cure (thermo-chemo-mechanical) was proposed to fit the elastic modulus data of the curing resin. This model correlates well with the experimental results offering improved accuracy than existing linear models and simpler than viscoelastic models. Rheology of the resin was investigated to obtain gelation, vitrification and viscosity information. The temperature-degree of cure-dependent viscosity was modeled empirically from the rheological data. The empirical models obtained for degree of cure, modulus and viscosity were used to predict the micro-level cure-induced strain of a curing composite and compared with experimental results.