Showing papers in "Applied Composite Materials in 2020"

Mechanical and Acoustic Properties of Alkali-Treated Sansevieria ehrenbergii/Camellia sinensis Fiber–Reinforced Hybrid Epoxy Composites: Incorporation of Glass Fiber Hybridization

Abstract: The intention behind this research work was to analyse the mechanical as well as acoustic behaviour of Sansevieria ehrenbergii (snake grass) / Camellia sinensis (waste tealeaf) fibers with glass fiber (GF) – reinforcement to form the hybrid epoxy composites. Fibers of S.ehrenbergii/C.sinensis were chemically modified for their effective usage as reinforcement in hybrid composites. Five combinations of hybrid composites were fabricated using hand-operated compression molding techniques by changing the percentage weight of snake grass fiber (SGF) and waste tea leaf fiber (WTLF). The results indicated that the mechanical behaviour of SGF/WTLF composites have been substantially enhanced by hybridization with GF. Enhanced mechanical behavior of hybrid composites is observed as an incremental percentage of SGF composition. The experimental findings show that the weight fraction of 25 wt.% WTLF reinforced with SGF shows a strong acoustic absorption coefficient (AAC) of 0.59 in the frequency range of 2000–6300 Hz as well introduces the potential for acoustic sound proofing applications, such as loudspeaker design, perforated panels, sound recording, and reproduction room. The morphological behavior of hybrid composites, such as fiber pullout, matrix crack, void formation, and interfacial bond between the binder and fibers were observed using a scanning electron microscope.

Fabrication and Characterization of Hemp Fibre Based 3D Printed Honeycomb Sandwich Structure by FDM Process

Abstract: Natural fibre composites have been trending in the industries recently due to their better recyclability, renewability, biodegradability. Fused Deposition Modelling (FDM) is one of the widely used additive manufacturing process for the fabrication of simple and complex structures. In this study, hemp/PLA 3D printed honeycomb sandwich structures were fabricated by FDM process and mechanical behaviour was characterized. Initially, the tensile behaviour of hemp fibre/PLA filaments and the 3D printed composite specimens with an infill angle of 0°/90°, -45°/ + 45° were investigated. Honeycomb cores were fabricated and their mechanical behaviour in flatwise, edgewise directions were analysed. Later, honeycomb sandwich structures were fabricated using core and skin parts. Compression and 4-Point bending tests were performed to characterize the mechanical behaviour. Analytical analysis was also performed to predict the mechanical properties of the honeycomb sandwich structure knowing the properties of the cell wall material. Some small-scaled automotive and aerospace prototypes were fabricated to assure the application of this methodology.

Damage Detection in Composites By Artificial Neural Networks Trained By Using in Situ Distributed Strains

Abstract: In this paper, a passive structural health monitoring (SHM) method capable of detecting the presence of damage in carbon fibre/epoxy composite plates is developed. The method requires the measurement of strains from the considered structure, which are used to set up, train, and test artificial neural networks (ANNs). At the end of the training phase, the networks find correlations between the given strains, which represent the ‘fingerprint’ of the structure under investigation. Changes in the distribution of these strains is captured by assessing differences in the previously identified strain correlations. If any cause generates damage that alters the strain distribution, this is considered as a reason for further detailed structural inspection. The novelty of the strain algorithm comes from its independence from both the choice of material and the loading condition. It does not require the prior knowledge of material properties based on stress-strain relationships and, as the strain correlations represent the structure and its mechanical behaviour, they are valid for the full range of operating loads. An implementation of such approach is herein presented based on the usage of a distributed optical fibre sensor that allows to obtain strain measurement with an incredibly high resolution.

A Modeling Method of Continuous Fiber Paths for Additive Manufacturing (3D Printing) of Variable Stiffness Composite Structures

Abstract: A modeling method of variable stiffness composite structures (VSCSs) with curved fiber trajectories has been developed. The fiber trajectories are aligned in the direction of maximum principal stress, and the VSCSs with variable fiber orientation and the variable fiber volume fraction are modeled on the basis of these trajectories. A material property degradation method taking into account the heterogeneity of material properties of the VSCSs is used to predict the ultimate load and model the progressive failure for a composite plate with a hole under tensile loading. It is shown that a transition from rectilinear reinforcement to curvilinear results in an increase in the ultimate load of the plate. The opportunity for simulation of a continuous fiber path for the VSCSs is presented, and the path could be used to produce the VSCSs by additive manufacturing (3D printing).

Effects of Impactor Geometry on the Low-Velocity Impact Behaviour of Fibre-Reinforced Composites: An Experimental and Theoretical Investigation

Abstract: Carbon-fibre/epoxy-matrix composites used in aerospace and vehicle applications are often susceptible to critical loading conditions and one example is impact loading. The present paper describes a detailed experimental and numerical investigation on the relatively low-velocity (i.e. <10 m/s) impact behaviour of such composite laminates. In particular, the effects of the geometry of the impactor have been studied and two types of impactor were investigated: (a) a steel impactor with a hemispherical head and (b) a flat-ended steel impactor. They were employed to strike the composite specimens with an impact energy level of 15 J. After the impact experiments, all the composite laminates were inspected using ultrasonic C-scan tests to assess the damage that was induced by the two different types of impactor. A three-dimensional finite-element (FE) model, incorporating a newly developed elastic-plastic damage model which was implemented as a VUMAT subroutine, was employed to simulate the impact event and to investigate the effects of the geometry of the impactor. The numerical predictions, including those for the loading response and the damage maps, gave good agreement with the experimental results.

Impact Response of Carbon/Kevlar Hybrid 3D Woven Composite Under High Velocity Impact: Experimental and Numerical Study

Abstract: The ballistic impact behavior of hybrid 3-dimentional woven composites (3DWC) is predicted through a novel numerical modeling technique and validated the outcome through experimental data. Continuum shell elements with Hashin failure criterion and cohesive surface contact algorithm with traction separation law are used to predict the damage behavior and failure mechanisms during the impact process at interply and intraply levels. Z-yarns are represented by the connector elements with uniaxial behavior having stress-based failure criterion. The proposed methodology predicted the different damage mechanisms during the impact process in comparison with the experimental data and estimated the residual velocities with acceptable accuracy. Different failure mechanisms incurred due to the hybrid nature of the material are also captured by the numerical simulation and the effect of z-yarns are truly depicted by the use of simple 1D elements over the different phases of perforation process. Overall, the finite element (FE) methodology by using simplest form of the elements, their constitutive and damage behavior gives promising results by sufficiently reducing the computational cost.

Finite Element Simulation of Tensile Preload Effects on High Velocity Impact Behavior of Fiber Metal Laminates

Abstract: As primary structures and protective structures, fiber metal laminates (FMLs) in practical application are always in preload states before possible impact damage threats. In this work, a nonlinear finite element (FE) model is developed to study the impact damage scenario where tensile preloaded FMLs are impacted by a hemispherical nose projectile at high velocities. In the modeling, the intra-layer damage in aluminum sheets and composite laminates and the delamination between adjacent plies are entirely included. The FE model is verified with available experimental results in non-preload condition and then applied to predict the high velocity impact behavior in uniaxial and biaxial tensile preload cases. The ballistic performance and damage response of representative FMLs with different preloads and impact velocities are discussed and analyzed in detail. The numerical results and modeling strategy here provides applicable reference for preloaded impact issues in other FMLs.

Investigation of Silica-Based Shear Thickening Fluid in Enhancing Composite Impact Resistance

Abstract: Laminated composite structures have attracted the interest of the modern industry due to their high performances and reduced weight when compared to traditional structural materials. However, they are very sensitive towards out-of-plane dynamic loading that can generate Barely Visible Impact Damage (BVID) within the structure and cause a drastic detriment of mechanical properties. One solution is proposed to overcome this problem by the hybridisation of the laminate stacking sequence using Shear Thickening Fluids (STFs) for absorption of large fractions of impact energy with a minimal damage generation. This work numerically investigated the impact response of Carbon Fibre Reinforced Polymers (CFRP) when a silica-based STF is embedded within the lamination sequence utilising an innovative Ls-Dyna-based Finite-Element Model (FEM). This was developed using an Arbitrary Lagrangian Element (ALE) approach in a fluid-structure interaction (FSI) analysis and calibrated with an experimental impact campaign to determine the best impact resistance as a function of the STF position along the thickness of the laminate. The results showed an improvement in impact resistance for all the hybrid configurations identifying the optimal STF location in the upper portion of the laminate with a reduction in absorbed energy of ~ 42%, damaged area of ~ 35% alongside an increase in contact force (~ 36%) with respect to conventional laminate with same stacking sequence and number of plies. The results showed that STF/CFRP structures can be successfully employed for applications in several advanced sectors including aerospace, automotive and energy (wind blades) representing an important step-up in the development of high-impact resistant hybrid composite structures.

Impact Damage Characteristics of Carbon Fibre Metal Laminates: Experiments and Simulation

Abstract: In this work, the impact response of carbon fibre metal laminates (FMLs) was experimentally and numerically studied with an improved design of the fibre composite lay-up for optimal mechanical properties and damage resistance. Two different stacking sequences (Carall 3–3/2–0.5 and Carall 5–3/2–0.5) were designed and characterised. Damage at relatively low energy impact energies (≤30 J) was investigated using Ultrasonic C-scanning and X–ray Computed Tomography (X-RCT). A 3D finite element model was developed to simulate the impact induced damage in both metal and composite layers using Abaqus/Explicit. Cohesive zone elements were introduced to capture delamination occurring between carbon fibre/epoxy plies and debonding at the interfaces between aluminium and the composite layers. Carall 5–3/2–0.5 was found to absorb more energy elastically, which indicates better resistance to damage. A good agreement is obtained between the numerically predicted results and experimental measurements in terms of force and absorbed energy during impact where the damage modes such as delamination was well simulated when compared to non-destructive techniques (NDT).

Detection of Damage in CFRP by Wavelet Packet Transform and Empirical Mode Decomposition: an Hybrid Approach

Abstract: The integrity of the CFRP specimens is tested using acousto-ultrasonic testing method. To validate the acousto-ultrasonic test mode, the specimens are tested before and after a Barely Visible Impact Damage induced by an impactor. A special model is created to use both Wavelet Packet Transform and Empirical Mode Decomposition, for decomposing the recorded waveforms. This mode also enables the reconstruction of the decomposed waveforms, discarding the residual signal in the parent waveform, and calculates the energy associated with each frequency band of the reconstructed signal. By using the percentage of energy recovered by the receiver compared to the signal sent through the specimen, the integrity of the specimens is identified. Moreover, the properties of each specimen and the extent of its damage, albeit qualitatively along the longitudinal and transverse directions can also be assessed by using this technique.

Direct Processing of Structural Thermoplastic Composites Using Rapid Isothermal Stamp Forming

Abstract: A novel rapid isothermal stamp forming process is proposed which enables the rapid manufacture of structural thermoplastic composite laminate parts directly from multilayer hybrid fabrics comprising stitched unidirectional carbon fibre-thermoplastic polymer veil. The process employs rapid-response variothermal tooling, allowing macro-scale (fabric forming/draping) and micro-scale (fibre wetting/laminate consolidation) composite material transformation processes to occur isothermally above the constituent polymer matrix melt temperature (Tm), thus manufacturing a composite component directly from a hybrid dry fabric in a single press cycle in a relatively short overall cycle time. The proposed rapid isothermal stamp forming (RISF) concept is presented, and details of the process are given along with some considerations made throughout the formulation of the process. As a result of the RISF process development work, candidate manufacturing parameters were derived, delivering parts that exhibit acceptable composite laminate microstructure and mechanical performance within a press station cycle time of 330 s.

Ananalytical and Experimental Study of T - Shaped Composite Stiffened Panels: Effect of 90° Plies in Stringers on Curing and Buckling Performance

Abstract: The effect on curing deformation and strength of 90° plies in stringers for composite T-shaped stiffened panel were presented by numerical analysis and experimental measurement. In this work, the finite element model (FEM) for curing deformation based on cure kinetics formulation was utilized. The model for buckling and failure based on Tsai-Wu failure criteria and incremental/ Newton -Raphson mixed iteration equation was established. The curing, buckling and post-buckling analysis were performed on composite T-shaped stiffened panels to obtain the deformation, the critical load and mode of failure, with different 90° plies-ratios in stringers. Furthermore, the experimental investigation has been carried out for specimens with different plies-ratios of 90° plies in stringers. The good agreement between the numerical results obtained by finite element method and the experimental ones demonstrated that this kind of numerical analysis could estimate appropriately the behavior of the structure. In addition, it was found that the 90° plies in stringers play an important role in reducing the curing deformation, but it has little effect on the axial compression loading capacity for composite T-shaped stiffened panel, which is useful for application in civil aviation aircraft.

Curing Cycle Optimization for Thick Composite Laminates Using the Multi-Physics Coupling Model

Abstract: A multi-objective optimization method which takes the multi-physics coupling characteristic into account is proposed to determine the cure cycle profile for polymer-matrix composites. First, a numerical model which considers the effects of heat transfer, cure kinetics, resin flow-compaction process has been developed to predict the temperature and degree of curing. The simulation results agree well with the experimental measurements from the previous publication to validate the practicability of the FE model. A surrogate model based on the Surface Response Method is built to make the solution feasible according to the entire calculation time. The surrogate model was integrated into the optimization framework to optimize cure cycle profile using NSGA-II algorithm. The results show that the duration of the cure time and the maximum gradient of temperature are about 44.8% and 34% shorter than in the typical cure profile, respectively. It is also shown that the multi-physics coupling characteristic should be considered in the optimization process for thick composite component.

A Cutting Force Prediction Model, Experimental Studies, and Optimization of Cutting Parameters for Rotary Ultrasonic Face Milling of C/SiC Composites

Abstract: Ceramic matrix composites of type C/SiC have great potential because of their excellent properties such as high specific strength, high specific rigidity, high-temperature endurance, and superior wear resistance. However, the machining of C/SiC is still challenging to achieve desired efficiency and quality due to their heterogeneous, anisotropic, and varying thermal properties. Rotary ultrasonic machining (RUM) is considered as a highly feasible technology for advanced materials. Cutting force prediction in RUM can help to optimize input variables and reduce processing defects in composite materials. In this research, a mathematical axial cutting force model has been developed based on the indentation fracture theory of material removal mechanism considering penetration trajectory and energy conservation theorem for rotary ultrasonic face milling (RUFM) of C/SiC composites and validated through designed sets of experiments. Experimental results were found to be in good agreement with theoretically simulated results having less than 15% error. Therefore, this theoretical model can be effectively applied to predict the axial cutting forces during RUFM of C/SiC. The surface roughness of the workpiece materials was investigated after machining. The relationships of axial cutting force and surface roughness with cutting parameters, including spindle speed, feed rate, and cutting depth, were also investigated. In order to identify the influence of cutting parameters on the RUFM process, correlation analysis was applied. In addition, response surface methodology was employed to optimize the cutting parameters.

On the Difference Between the Tensile Stiffness of Bulk and Slice Samples of Microstructured Materials

Abstract: Many materials with a microstructure are statistically inhomogeneous, like casting skins in polymers or grain size gradients in polycrystals. It is desirable be able to account for the structural gradient. The first step is to measure the location dependent properties, for example by tensile testing of thin slices. Unfortunately, the slices properties can differ significantly from the bulk properties, since the slices lack a scale separation in one direction. For Polypropylen, we measured that Young’s modulus of the slices is approximately 70% of the respective bulk value. We have identified three significant effects, all making the slices appear softer than the bulk material: We examine and quantify these effects in the linear elastic range for matrix-inclusion-structures and an interpenetrating-phase-structure. Some approaches on how the slice- vs bulk difference can be estimated are given.

Influence of Fiber Orientation and Adhesion Properties On Tailored Fiber-reinforced Elastomers

Abstract: This research focuses on the investigation of endless fiber-reinforced elastomeric materials with special tailoring by different fiber orientations in the composite structure. Therefore, a modified testing device including a suitable specimen production was carried out and the comparability of tests conducted at different test scales (micro- to macro testing level) was proven. Two elastic matrix materials (silicone and polyurethane) and reinforcing fiber types (glass- and polyester fibers) were investigated in all combinations. Due to the important effect on the shear behavior during the deformation of textiles significantly influenced by the fiber orientations of the warp- and weft-yarns, a testing plan was established by using one material combination as a reference setting. Generally, the results reveal a good comparability between different testing levels for the same fiber-matrix combinations and the modified composite testing device has been proven. Furthermore, the significant influence of different fiber orientations on the shear stiffness was investigated.

The Structural Integrity of Composite Materials and Long-Life Implementation of Composite Structures

Abstract: Empirical or semi-empirical design methodologies at the macroscopic scale (structural level) can be supported and justified only by a fundamental understanding at the lower (microscopic) size scale through the physical model. Today structural integrity (SI) is thought as the optimisation of microstructure by controlling processing coupled with intelligent manufacturing of the material: to maximise mechanical performance and ensure reliability of the large scale structure; and to avoid calamity and misfortune. SI analysis provides quantitative input to the formulation of an appropriately balanced response to the problem. This article demonstrates that at the heart of the matter are those mechanisms of crack nucleation and growth that affect the structural integrity of the material: microscopic cracking events that are usually too small to observe and viewed only by microscopy.

Uncertainty in Fibre Strength Characterisation Due to Uncertainty in Measurement and Sampling Randomness

Abstract: Carbon fibres have exceptional mechanical properties and are used for critical structural applications such as composite pressure vessels and aerospace components. For such high performance applications, reliability-based designs and lifetime assessments require very accurate strength models. Accuracy of the predictions made by composite strength models depend on realistic material properties of constituents, which are used as input. In practice however, fibre strength properties reported by different sources show significant variations. The work described here aims at understanding the influence of measurement uncertainty and sampling randomness on the uncertainty in calculated tensile strength distribution parameters. Tensile strength data for T700 carbon fibres obtained from single fibre testing process has been analysed for uncertainties. A parametric bootstrap method has been used for the evaluation. It has been shown that although both the causes studied of uncertainty are critical, the sampling randomness has a larger influence on the uncertainty of fibre strength, as compared to the uncertainty due to measurement. Choosing an insufficient sample size for analysis can thus result in uncertain or even inaccurate fibre strength properties, which would limit the reliability of composite strength models. The knowledge of the causes and effects of these uncertainties can help in taking appropriate measures for improving the accuracy of results. This would thereby enhance the capability of composite strength models to estimate the behaviour of different composite structures more accurately.

Mechanical Properties and Growth Mechanism of TiB 2 -TiC/Fe Composite Coating Fabricated in Situ by Laser Cladding

Abstract: A TiB2-TiC/Fe composite coating was successfully produced on a Q235 substrate by laser cladding through in-situ reactions among 60TiFe, B4C, Cr, Ni, and Si preset powder mixtures. Based on the available literature, scanning electron microscopy images of the mixed precursor powder and coating layer, and corresponding electron dispersive spectroscopy and X-ray diffraction results from the produced coating, the formation mechanism of the TiC-TiB2 composite during laser cladding was determined. The results show that the coating was mainly composed of α-Fe, TiB2, TiC and (Fe, Cr)7C3, where the TiB2 had a dark grey rectangular shape and TiC had a light grey spherical shape. Most of the TiC particles were attached to the TiB2, which means that TiB2 particles were formed before the TiC. The microhardness of the composite coating approached 1260 HV0.2, which shows that the microhardness of the composite coating was more than 7 times that of the Q235 substrate. Furthermore, the wear performance of the coating was obviously improved, to approximately 15 times that of the substrate.

High-Speed Forming of Continuous Fiber Reinforced Thermoplastics

Abstract: Forming processes of continuous fiber reinforced thermoplastic materials are oftentimes limited to high volume production due to the high costs for tooling and processing machines. This study suggests the combined use of a cold and simple tool and high forming speeds to reduce tooling and processing costs and enable the usage of common stamping machines. Half sphere samples are produced from single and two-layer polypropylene and glass fiber organo-sheets in a custom built drop tower and analyzed for their geometry, degree of re-consolidation, surface quality and potential fiber damage using a variety of microscopy techniques. While only mediocre degrees of re-consolidation and limited surface qualities can be achieved with the combination of a cold tooling and state-of-the-art forming speeds of 0–0.5 ms−1, the usage of a higher forming speed of 3 ms−1, vastly improves surface qualities and the degree of re-consolidation without any detectable fiber damage. This effect is more pronounced in the dual layer material. Extensive knowledge on the forming behavior of continuous fiber reinforced thermoplastics at high cooling rates and high speeds of deformation is required for sufficient process control and future studies need to further elaborate and quantify the influencing factors and limits of high-speed forming of continuous fiber reinforced thermoplastics.

A Novel Method to Improve Temperature Uniformity in Polymer Composites Microwave Curing Process through Deep Learning with Historical Data

Abstract: Compared with processing methods using conductive heating, microwave processing technology has many advantages such as its extremely short processing time and low energy consumption. However, the uneven temperature on the composite surface resulted from the uneven electromagnetic field distribution have become a big problem. Because the traditional model-based approach was difficult to establish the relationship between the composite temperature behaviors and microwave control strategies, existing methods mainly alleviated this problem by generating a relative movement between the microwave field and the object being heated, which cannot essentially achieve a uniform temperature distribution due to the uncertainty of the random compensation principle. In this paper, a data-driven method was proposed to solve this problem using an optimized convolutional neural network with extensive historical data. On this basis, the monitored uneven temperature distribution on the composite surface was accurately compensated in real time. Experimental results indicated that a reduction of ~53% in temperature difference was achieved compared with existing methods.

3D In-Situ Characterizations of Damage Evolution in C/SiC Composite under Monotonic Tensile Loading by Using X-Ray Computed Tomography

Abstract: The damage evolution and fracture behavior in the bulk of C/SiC material under monotonic tensile loading have been investigated with the 3D in-situ observations by using X-ray CT. Crack initiated inside the matrix within 0.02 mm below surface when the load was only 19% of the failure strength, and propagated to the surface of matrix and towards the interior of specimen by breaking fibers and matrix when the load was above the elastic limit. With the further increasing of loading, other fiber breaks, matrix breaks and delaminations were observed to initiate and propagate both on the surface and in the bulk of specimen, while the cracks nucleating in the bulk of specimen are generally located at the laminae with a high volume fraction of pores. With the further propagations of cracks, the specimen split in the laminae with a large quantity of pores, while the fiber drawings results in the final fracture in the laminae without a large quantity of pores. The novel method being proposed to characterize the distribution of pores in this paper highlights the relation between the distribution of pores in the bulk of the studied material and cracks initiations and final fracture.

Influence of Large Framed Mold Placement in Autoclave on Heating Performance

Abstract: For large composite parts manufactured by autoclave curing process, temperature uniformity of the mold is essential to ensure final part quality. This paper aims to investigate the influence of mold placement variation in autoclave on heating performance of a large framed mold and find the optimal mold placement parameters for improving the temperature uniformity and heating rate. Firstly, a computational fluid dynamics (CFD) based autoclave simulation model is established and validated, which offers reliable prediction of the mold temperature field and flow distribution in autoclave. Then, numerical experiments are performed based on the autoclave simulation model and response surface methodology (RSM) to establish relations between mold placement variables and responses including temperature uniformity and heating rate. Finally, using the established regression model, multi-objective optimization is conducted considering both temperature uniformity and heating rate. The optimal mold placement parameters are obtained successfully which improves the temperature uniformity significantly with little change in heating rate comparing to the commonly adopted mold placement approach. The strategies provided by mold placement optimization can be applied for various large framed molds in composite manufacturing improving the autoclave curing process.

Fire Safety Assessment of Epoxy Composites Reinforced by Carbon Fibre and Graphene

Abstract: This paper presents a coupled numerical investigation to assess the reaction to fire performance and fire resistance of various types of epoxy resin (ER) based composites. It examines the fire response of carbon fibre (CF) reinforced ER (CF/ER), ER with graphene nanoplatelets (GNP/ER) and CF reinforced GNP/ER (CF/GNP/ER). Thermal, physical and pyrolysis properties are presented to assist numerical modelling that is used to assess the material ability to pass the regulatory vertical burn test for new aircraft structures and estimate in-fire and post-fire residual strength properties. Except for the CF/GNP/ER composite, all other material systems fail the vertical burn test due to continuous burning after removal of the fire source. Carbon fibres are non-combustible and therefore reduce heat release rate of the ER composite. By combining this property with the beneficial barrier effects of graphene platelets, the CF/GNP/ER composite with 1.5 wt% GNP and 50 wt% CF self-extinguishes within 15 s after removal of the burner with a relatively small burn length. Graphene drastically slows down heat conduction and migration of decomposed volatiles to the surface by creating improved char structures. Thus, graphene is allowing the CF/GNP/ER composite panel to pass the regulatory vertical burn test. Due to low heat conduction and reduced heat release rate, the maximum temperatures in the CF/GNP/ER composite are low so the composite material retains very high in-fire and post-fire mechanical properties, maintaining structural integrity. In contrast, temperatures in the CF/ER composite are much higher. At a maximum temperature of 86 °C, the residual in-fire tensile and compressive mechanical strengths of CF/GNP/ER are about 87% and 59% respectively of the ambient temperature values, compared to 70% and 21% respectively for the CF/ER composite that has a temperature of 140 °C at the same time (but the CF/ER temperature will be higher due to continuing burning). Converting mass losses of the composites into char depth, the post-fire mechanical properties of the CF/GNP/ER composite are about 75% of the ambient condition compared to about 68% for the CF/ER composite.

Fabrication, Design and Application of Stretchable Strain Sensors for Tremor Detection in Parkinson Patient

Abstract: Due to increasing demand for wearable health monitoring devices, stretchable electronics have developed rapidly in recent years. For human motion detection, strain sensors must be highly stretchable, sensitive, and durable. Another important factor is low-cost fabrication. As such, the sensors in this research were made of carbon nanotubes (CNTs) and graphene in Polydimethylsiloxane (PDMS) using a solution casting method. In order to improve bending sensitivity, slits were created on the sensor surfaces. The strain sensors were placed on an index finger in order to detect and monitor the hand tremors of Parkinson’s patients. Furthermore, a wearable glove system with hardware components including an Arduino Nano controller, stretchable strain sensors, a Real Time Clock (RTC) Module, and a Micro SD card Adapter was developed for practical use in everyday life.

Finite Element Analysis of the Crack Deflection in Fiber Reinforced Ceramic Matrix Composites with Multilayer Interphase Using Virtual Crack Closure Technique

Abstract: Crack deflection along the interphase for fiber reinforced ceramic matrix composites (CMCs) is an important condition upon which the toughening mechanisms depend. The multilayer interphase is designed and developed to enhance this deflection mechanism. Combined with the virtual crack closure technique, a finite element model was proposed to predict the competition between crack deflection and penetration in multilayer interphase of CMCs. The model was used to analysis the propagation of primary matrix crack in a SiCf/SiCm composite with (PyC/SiC)n multilayer interphase. The effects of the number of sublayers, thicknesses of sublayers and thermal residual stress (TRS) on the energy release rate and the crack deflection mechanisms were studied. Results show that the multilayer interphase increases the ability to deflect the matrix crack at interfaces between sublayers. Moreover, the number of sublayers shows a larger effect than the thicknesses of the sublayers. The influence of TRS is much complex and needs to be evaluated accordingly. The research provides an analysis tool for promoting the toughening design of CMCs.

Composite Manufacturing Cost Model Targeting on Design Optimization

Abstract: As applications of composite material increasingly increase in the aviation sector, its manufacturing cost is now identified as a bottle neck, which limits the market competitiveness in terms of cost-performance efficiency To estimate the manufacturing cost of composite structures at the early design stage, this research proposes a manufacturing cost model based on process simulation and represents the cost in the form of “Equivalent Working Hour” (EWH) The research also introduces the “Structural Complexity Element” (SCE) and “Hourly Rate Factor” (HRF) to ensure and improve the accuracy of the model Then, the model is applied on a composite wing structure to calculate and analyze the manufacturing costs of two structure designs to be manufactured through manual lay-up, automated tape lay-up/fiber placement, autoclave or out-of-autoclave curing, mechanical assembly, and co-cure or adhesive bonding The results verified the effectiveness of the model

Modeling Shear Behavior of Woven Fabric Thermoplastic Composites for Crash Simulations

Abstract: Woven fabric thermoplastic composites possess high specific strength and stiffness along with thermoformability. To utilize the full potential of these materials to achieve better crash-safe designs in automotive structural parts, the measurement of non-linear shear behavior and its material modeling for FEM simulations is required. The standard testing method was used to measure the pure shear behavior of woven fabric composites. These results were compared with the shear behavior of material in the presence of normal stresses along the fiber direction. Tensile and compression cyclic testing of ± 45° laminate were carried out to measure the stiffness degradation and hardening of the material in the presence of tensile normal and compression normal stress. A methodology is proposed for taking into account the differences in shear behavior under different loading directions in an FEM simulation. Based on the experimental evidence, improvements in the mathematical description of plasticity and damage in continuum damage mechanics models are proposed. The model was implemented as a user-defined material subroutine (VUMAT) for Abaqus. The experimental results from coupon tests were used to verify the results of a single element simulation. Finally, a three-point bending test was used to validate the predictions of the user material model.

Experimental Assessment of Residual Integrity and Balanced Mechanical Properties of GFRP/CFRP Hybrid Laminates under Tensile and Flexural Conditions

Abstract: In this work, the hybrid effect on both tensile and flexural properties as well as the residual integrity of six hybrid unidirectional laminates of carbon/glass fibers with epoxy resin matrix was experimentally assessed. The experimental results showed that the best balance on both tensile and flexural properties was obtained by a high degree of dispersion of low and high elongation reinforcement within the interply hybrid configuration. The [G/C/G]s hybrid condition exhibited a hybrid effect ranging from 1.30 to 1.87, which means an increase of 30% and 87% for the laminate mechanical performance, respectively. Furthermore, increases in both the tensile residual integrity of 3.67 times, and the flexural residual integrity of 1.26 times were obtained, compared to the reference laminates.

Impact Response of Curved Composite Laminates: Effect of Radius and Thickness

Abstract: This paper presents the results of drop-weight impact testing (5 J to 30 J) on curved ±55° E-glass-epoxy laminates of varying radii and wall thickness. Three radii (75 mm, 100 mm, and 125 mm) on laminates with an effective wall thickness of 2.5 mm, and three wall thicknesses (2.5 mm, 4.1 mm, and 6.6 mm) with a radius of 100 mm were investigated. The damage pattern remained consistent, with the exception of the damage area, across the tested energies and was dominated by internal matrix cracking and multiple delaminations. However, no damage was recorded following a 5 J impact on the 2.5 mm thick laminates with 100 mm and 125 mm radii, all energy was absorbed elastically, while the laminate with a 75 mm radius of curvature developed a damage area of over 80 mm2. The thicker laminates showed a reduced overall damage area but a greater number of delaminations. The relationship between laminate thickness and delamination threshold load was found to be in line with impact testing of flat plates, varying with the laminate thickness to the 3/2 power. However, the simplified beam theory and a fracture mechanics model developed for the prediction of delamination threshold of flat plates was found to underestimate the delamination threshold load (DTL) of the curved laminates studied by about 40%. An increase in the laminate’s flexural modulus of a factor of two is required to bring the model’s predictions in line with the DTL values measured experimentally, highlighting how curvature can enhance bending stiffness and alter damage evolution. Finally, a significant finding is that the DTL of the curved plates is around 15% lower than the value measured for the whole cylindrical pipe of same specifications. Testing curved sections rather than a whole pipe could reduce effort, but further work is required to confirm this statement.