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Spacesuits and spacecraft must endure high velocity impacts from micrometeoroids. This work considers the impact of 100 μm diameter projectiles into composite targets at velocities from 0.5 km/s to 2 km/s. This work begins by presenting an energy-based theoretical model relating depth of penetration (DoP) and impact force to impact velocity, characteristic time, and threshold velocity and force. Next, this work compares numerical simulations of normal impact on composites to the theoretical model. Numerical simulations are conducted with LS-DYNA and the well-known composite model, MAT-162. The numerical models consider unidirectional S2-glass fiber reinforced SC-15 epoxy composite laminates. The numerical model shows good correlation with the theoretical model. The numerical model also investigates lateral impact, parallel to the fiber direction, and oblique impact at angles from 30° to 82.5°. This work decomposes oblique impact into normal and lateral components, and compares them with normal and lateral impact results. The results show good correlation of the normal component of oblique results with the theoretical model. This numerical and theoretical study focuses on DoP, velocity, and penetration resistance force as functions of time. The theoretical model and numerical simulations are used to determine new DoP parameters: characteristic time of depth of penetration and threshold impact velocity. These models are a first step in developing the capability to predict DoP for oblique, microscale, high-speed impact on composite materials.

In this study the effects of thermal shock on the impact damage resistance, damage tolerance and flexural strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates with balanced and symmetric layup were gradually heated to 1200°C in an air-based furnace and held for at least 30 min before being removed and immersed in water at room temperature. The laminates were then subjected to low velocity impacts via a hemispherical steel impactor. The resultant damage was characterized non-destructively, following which the laminates were subjected to compression tests. Three-point bend tests were also performed to evaluate the effect of thermal shock on the flexural strength and related failure modes of the laminates. Thermally shocked laminates showed smaller internal damage and larger external damage areas in comparison to their pristine counterparts. For the impact energy and resultant damage size considered, the residual compressive strengths for the thermally shocked and pristine laminates were similar.

Friction stir processing (FSP) is a solid-state deformation process that refines the surface microstructure. FSP is used to fabricate the surface composites and improve the mechanical properties, e.g., strength, hardness, ductility, wear, corrosion resistance, abrasion resistance, etc. Nowadays, FSP is a recommended method for preparing surface composite laminates made up of lightweight aluminium alloys, resulting in uniform distribution of the reinforcements into the matrix the refined microstructure at the surface up to a certain depth without affecting the bulk properties. In composites' fabrication by FSP, the refined microstructure is obtained at a temperature below the melting point. It eliminates the defects caused during other methods of fabrication that involve melting, solidification, etc., and enhanced mechanical properties evolve. This paper represents a review of the research work in FSP in the fabrication of hybrid layered composites in the context of sensor data monitoring and process control. In FSP, various sensors like- force, temperature, vibration, etc., are used to collect the data. The data is analyzed to monitor the machine condition, reduce the tool wear, improve surface microstructure, predict process anomalies, etc. This work in FSP is quite rare and has an excellent scope to be studied further.

The aim of this study was to find the mechanical characteristics of quasi-isotropic intra-ply woven Carbon-Kevlar/Epoxy hybrid composite by experimental investigation. The composite laminate configuration of quasi-isotropic, symmetric, balanced and intra-ply hybridization was selected in accordance with applications requiring thin and isotropic material properties. The composite laminate was fabricated using hand-layup and vacuum-bagging techniques and ASTM International (formerly known as American Society for Testing and Materials) standards were followed for all the tests. The tests conducted in this study include Void-content and density test, Tensile test, Flexural test, Izod impact test, Inter-laminar shear (ILSS) test and Scanning Electron Microscopy (SEM) test. The void test was conducted to ensure the fabrication quality of the composite laminate. Different mechanical tests were conducted to find its properties under different loading conditions and SEM was used to understand the failure modes involved in the fracture of a tensile specimen. The material showed moderate and balanced mechanical properties such as good bending and impact behavior that can be used in applications that require isotropic properties with both bending and impact strengths. The tensile, flexural, impact and inter-laminar shear strengths of the material determined by experimental investigation are 270 MPa, 196.6 MPa, 1440.4 J/m and 17.4 MPa respectively. SEM analysis revealed that matrix cracks, fiber pull out, fiber–matrix debonding, fiber breakage and delamination were the major failure modes in the fracture of the tensile test specimen.

Carbon-fiber reinforced polymer composite materials are used throughout industry for their excellent mechanical properties; in particular, these composites boast high specific stiffnesses and specific strengths. However, current limitations on manufacturing, which vary greatly based on the technology that is utilized, restrict access to composite materials in a variety of applications. Traditional wet hand-layups offer a large diversity of viable constituent materials, but the fabrication geometry is limited and the manual process is time-consuming. In contrast, fiber 3D-printing (F3DP) allows for the production of complex geometries and requires little manual labor. In this study, laminates with continuous carbon fiber reinforcement printed using a commercially-available 3D printer are compared to carbon fiber fabric-resin composites produced using manual layup techniques. Cross-ply [0,90,0,90,0]T laminates were fabricated and subject to mechanical testing in uniaxial tension and flexure. After normalization with respect to fiber volume fraction, we found that the tensile strength and stiffness of cross-ply carbon fiber composites manufactured using F3DP were higher than the tensile strength and stiffness of cross-ply specimens manufactured by a traditional hand-layup method; however, the hand-layup specimens exhibited higher strength and stiffness in flexure. The difference in material properties evident between the two fabrication methods suggests that each has its own suitable application. We anticipate that further studying the failure response of printed, fiber-reinforced composite materials to various loading modalities will give insight into potential areas of improvement for F3DP material selection and printing processes, particularly relating to void reduction. On a broader scale, comparing and analyzing the mechanical properties of composite laminates produced in these various methods will provide perspective on the viability of novel additive manufacturing methods for large-scale production and industrial applications.

A study of composite laminates under tension–torsion biaxial loading is presented. The focus is placed on fatigue lives of composite laminates under different tension–torsion biaxial fatigue loading paths. A macro-meso model used to predict multiaxial fatigue life of composite laminates is also presented in this paper. Firstly, a macro-scale 3D RVE corresponding to composite laminates is established to determine strain components in the material principal direction of each layer for each biaxial stress ratio. Secondly, a meso-scale 3D RVE corresponding to each layer with fibers distributed randomly is established, with progressive damage prediction method, biaxial strength of composite laminates can be predicted, and the final failure layer can be confirmed. Thirdly, select any one of fatigue loading path at which the final failure of composite laminates is fiber failure (matrix failure) to establish the reference curve for fiber (matrix). Finally, with reference curve, fatigue life of composite laminates under any biaxial loading path can be predicted. And numerical results show good agreements with experimental data.

Glass laminate aluminum reinforced epoxy (GLARE) mixes a layer of aluminum with fiber-reinforced epoxy to constitute a hybrid composite. During this investigation, plain E-glass fiber/epoxy specimen in addition to hybrid composite laminated epoxy specimens reinforced with both E-glass fiber and wire meshes of aluminum were produced. Tensile, bending, and hardness tests were performed to investigate how inserting Al wire meshes through thickness of the specimen in place of glass fiber layers affected the material mechanical characteristics. The characteristics of the generated hybrid laminates represented by strength and ductility were greatly influenced by varying the position and orienting direction of the aluminum wire mesh ply. Inclusion of Al wire mesh in the outer layers significantly causes deterioration in material tensile and bending strengths. The tensile strain as well as bending strain, on the other hand, were improved as a result of incorporating Al wire meshes by 51.3 percent and 153.4 percent, respectively.

Recently, we corrected the Green's functions for holes/cracks in composite laminates under coupled stretching-bending deformation. Through these corrected Green's functions, the fundamental solutions required for the special boundary element of holes/cracks in composite laminates are derived. By the use of dual coordinates, the derived fundamental solutions can be further applied to the cases of inclined holes and cracks. Moreover, a formula evaluating the stress intensity factors by using boundary nodal displacements and tractions is derived. With these closed-form solutions, the special boundary element developed in this study can deal with various kinds of hole/crack problems in composite laminates. Their loads can be in-plane tension, compression, or shearing, out-of-plane force, bending or twisting, distributed or concentrated, on the surfaces or along the edges; their boundaries can be simply supported, clamped, or free edges; their defects can be a hole or a crack with horizontal or inclined orientation; their laminates can be symmetric or unsymmetric. No matter which kind of conditions, no meshes are required on the hole and crack surfaces. And the stress intensity factors of cracks can be calculated directly without requiring any meshes along the crack surfaces or near the crack tip.

The optimal design of laminates of interlayer hybrid lamination with multicouplings is significantly beneficial to enhance the mechanical properties and reduce the cost of composite structures. The...

Glass laminate aluminum reinforced epoxy (GLARE) mixes an extremely thin ply of aluminum wire mesh layers with epoxy strengthened with fibers to create a hybrid composite laminates. During this investigation, plain E-glass fiber/epoxy specimens in addition to specimens with epoxy laminates reinforced with both E-glass/fiber, and wire meshes of aluminum were created. Meshes made of aluminum wire were used to increase the toughness of the E-glass fiber/epoxy combination. Tensile, bending, and hardness tests were performed to see how inserting Al wire meshes through thickness of the specimen in place of glass fiber layers affected the material mechanical characteristics. According to the outcomes from results, an influence on strength, toughness, and ductility of laminates due to using Al wire mesh instead of glass fiber. The characteristics of the generated hybrid laminates were greatly influenced by the varying position and the orienting direction of the aluminum wire mesh ply. Inclusion of Al wire mesh in the outer layers significantly made deterioration in material tensile strength and bending strength. The tensile strain also bending strain, on the other hand, were improved by 16.95 percent and 117 percent, respectively.

A new family of composite laminates could revolutionize composite structures to be lighter, stronger, easier to understand and design, and faster and lower cost to manufacture. For the last 60 year...

Low-velocity impact is one of the most critical load factors for composite laminates. Indeed, for structures submitted to low-energy impacts or small-object drops, such as tools during assembly or maintenance operations, composite laminates reveal a brittle behavior and can undergo significant damage in terms of matrix cracks, fiber breakage, or delamination. This damage is particularly dangerous because it drastically reduces the residual mechanical characteristics of the structure, and at the same time can leave very limited visible marks on the impacted surface. Impact damage tolerance is therefore an important design consideration for aircraft composite structures. The objective is to prove the composite structure can withstand the required loading, even with impact damage, and in particular if the impact is undetectable. The complexity of this design consideration is that it is necessary to consider, on one hand the impact damage, or more precisely the loss of residual strength due to the impact; and on the other hand, the impact detectability, or more precisely the permanent indentation left by the impact. The goal of this article is to present the concept of impact damage tolerance applied to aircraft composite structures.

High-velocity impact of foreign objects such as small stones will produce complex damage in composite laminates, which will severely degrade residual strength. This chapter first describes high-velocity impact tests for carbon fiber-reinforced plastic (CFRP) laminates and then observes damage states caused by near-perforation impacts. Extensive delamination and fiber breaks as well as matrix cracks appeared regardless of the stacking sequence. This study also quantitatively evaluates the influence of the stacking sequence and the material system (i.e., the presence or absence of toughened interlayers) on the damage area. Finally, the mechanisms of high-velocity impact damage in CFRP laminates are discussed, based on the observations.

Composite laminates employed in various sports products are usually subjected to large-deflection dynamic bending during their service. The chapter first describes the experimental characterisation of composites as well as investigation of various damage modes ensued under these loading conditions replicated by means of Izod-type dynamic tests. It then describes the development of three-dimensional finite-element models employing a cohesive-zone method to study the onset, progression and interaction of some damage modes observed experimentally. The developed numerical models are capable of simulating damage mechanisms in laminates and their interaction observed in the tests.

Fibre metal laminates (FMLs) are layered materials based on stacking arrangements of metals and fibre reinforced plastic (FRP) composite laminates. These hybrid fibre metal laminates combine the advantages of both metallic materials and the reinforced hard and strong fibrous materials. A series of low velocity impact and tensile tests were carried out on the fabricated hybrid fibre metal laminates with different orientations and stacking sequences. Aluminium metal, carbon and glass fibres were the layers used for fabricating the hybrid composites and the fabrication was done by varying the position and orientation of the laminates and as well as the stacking sequences. The effect of the different stacking sequence of the metal laminates and the fibre layers on the impact and tensile strengths of the hybrid composites are studied. The stress-strain curve analyses were carried out for tensile properties, while the force-time and energy-time curves were analysed for impact charcteristics of the developed composites.

The low-velocity impact perforation behavior of fiber-metal laminates (FMLs) is evaluated by analytical modeling. Four different FML layups consisting of glass fiber/epoxy layers and titanium alloy...

The advocacy of carbon neutrality and circular economy encourages people to pursue self-healing and recycling of glassy thermoset polymers in a more realistic and energy-saving manner, the best being intrinsic healing under room temperature. However, the high mechanical robustness and healing ability are mutually exclusive because of their completely opposite requirements for the mobility of the polymer networks. Here, we report a dual-cross-linked network by slightly coupling the low-molecular-weight branched polyethylenimine with an ester-containing epoxy monomer in a nonstoichiometric proportion. The highly mobile and dense noncovalent hydrogen bonds at the chain branches and ends can not only complement the mechanical robustness (tensile strength of 61.6 MPa, elastic modulus of 1.6 GPa, and toughness of 19.2 MJ/m3) but also endow the glassy thermoset polymer (Tg > 40 °C) with intrinsic self-healing ability (healing efficiency > 84%) at 20 °C. Moreover, the resultant covalent adaptive network makes the thermoset polymer stable to high temperatures and solvents, yet it is readily dissolved in ethylene glycol through internal catalyzed transesterification. The application to room temperature delamination healing and carbon fiber recycling was demonstrated as a proof-of-concept.

In this paper, the modified h-BN coating was coated on the prepreg sheets; then, the carbon fiber/epoxy composite laminates were prepared by compression molding. The through-thickness thermal conductivity, mechanical and thermomechanical properties of the laminates were studied, respectively. The results show that h-BN particles, which are flaky shape with a diameter of about 0.6 μm and thickness of about 70 nm, have been evenly incorporated into the composites, and the thermal stability, through-thickness thermal conductivity, impact strength and glass transition temperature (Tg) of the composites are improved accordingly. When the BN content is 10 m%, the initial thermal degradation temperature (Tinitial) of the prepreg is 370 ℃, which is 10 ℃ higher than that of unmodified prepreg. When the BN content is 7 m%, the thermal conductivity of the laminates reaches 0.9 and 1.0 W·m−1·K−1 at 25 and 100 ℃, respectively, which are 114% and 111% higher than that of pure laminate. When the content of BN is 5 m%, the impact strength of the laminate reaches the highest value of 225 kJ·m−2, which is 15.4% higher than that of pure laminate. BN particles form a dense heat conduction network, thus delaying the thermal degradation of the resin and improving the thermal conductivity. This study provides a facile path to fabricate composite laminates with the integrated structure and function.

Fibre Reinforced Plastic (FRP) materials are widely used in several key engineering applications such as ships, aircraft, wind turbine blades, helicopter blade, automobiles, and other transportation vehicles because of their mechanical properties and tailoring capabilities.Carbon and glass fibres are the most popular fibre reinforcements used for composite components. In the present study, two different stacking sequences, (0 degrees) and (0/90 degrees), are selected to study effect of fibre hybridization on flexural performance using three-point bending tests. Materials used are E-glass and T-300 carbon fibres in an epoxy matrix and the laminates were produced by resin transfer moulding methods. Fracture surfaces of composite laminates were examined using a scanning electron microscope. The results showed that the flexural strength, modulus and strain at failure of unidirectional and bidirectional composite laminates were strongly influenced by stacking sequences, fibre orientation and the hybrid ratio of the fibres. A higher flexural modulus was achieved when carbon fibres were placed on the compressive side. Hybrid specimens showed higher flexural strength and modulus by 21.08% and 145.39%, respectively, compared to the pure glass fibre reinforced laminates. On the other hand, flexural strength and modulus of hybrid specimen were less by 6.50% and 8.20%, respectively, as compared to carbon fibre reinforced specimens. Stacking sequences and hybrid ratio of glass/carbon fibre reinforced specimens were investigated with a view towards improving the mechanical properties of hybrid composites.

To better guide the manufacturing of bamboo-wood composite laminates, classical theory, first-order shear theory, and finite element method were used to predict the elastic modulus and deflection of bamboo-wood composite laminates. The influence of the adhesive layer on the elastic modulus and deflection of composite materials was considered. The effect of transverse shear on the mechanical properties of materials became smaller and smaller with an increasing span-to-height ratio. The effects of the adhesive layer on the elastic modulus and deflection were ± 0.5% and -0.1% to 0.3%, respectively. The transverse elastic modulus and mid-span deflection predicted by the three methods were quite different from the experimental results. When the span-to-height ratio was equal to 20, the prediction error of longitudinal elastic modulus by the three methods was less than 6%, which can be used to predict the elastic modulus of composite materials. The results provide a novel method to predict the properties of bamboo-wood composite laminates.

This work presents the results of an experimental study performed in carbon/epoxy composite materials manufactured using a ply-level hybridization technique. The aim of the study is to investigate the potential of such hybridization technique to promote pseudo-ductile failure, and to enhance fracture toughness. Two thin-ply carbon-epoxy systems and three different carbon-carbon hybrid lay-ups are considered. Both strength and fracture tests are performed on the manufactured laminates and the properties of the hybrid materials are compared to those of the baseline non-hybrid composites. Digital Image Correlation and post-mortem X-ray imaging are used to analyze the fracture process of the different materials. The comparison of the mechanical response of the different materials demonstrates that, by means of thin ply hybridization, a pseudo-ductile failure in tension can be obtained, associated with fibre fragmentation. However, the hybridization seems not to be responsible for the increased fracture toughness that is ascribable to the ply-thickness effect.

This paper presents a new resistance element welding process capable of producing invisible lap joints between steel-polymer-steel composite laminates. The process involves pre-drilling a flat-bottom hole in each laminate to remove the polymer core and one of the steel sheets, and positioning a cylindrical insert inside the two adjoining holes for subsequent resistance welding. Finite element modeling is utilized to construct the weldability lobe and to identify the parameters that lead to the formation of acceptable joints. Experimental results confirm the applicability of the process to produce invisible lap joints without signs of material protrusions or local indentations resulting from squeezing the polymer out to create contact between the steel sheets. Destructive peel and shear tests allow determining the maximum forces that the joints can safely withstand and comparing their performance against alternative joined by forming lap joints in which the mechanical interlocking is also hidden inside the laminates.

The development of fused filament fabrication has extended the range of application of additive manufacturing in various areas of research. However, the mechanical strength of the fused filament fabrication–printed parts were considerably lower than that of parts fabricated by other conventional methods, owing to the observed anisotropic behaviour and formation of voids by weak interlayer diffusion. Intense studies on the effect of design and process parameters of the printed parts on the mechanical properties have been done, whereas studies on the effect of build orientations and raster patterns needs special concern. The main aim of this work is to fabricate parts printed using quasi-isotropic laminate arrangement of rasters, achieved by a raster layup of [45/0/−45/90]s, and to compare their mechanical properties with those of the commonly used 0°/90° (cross) and 45°/−45° (crisscross) raster oriented parts. The quasi-isotropic–oriented samples were observed with improved mechanical behaviour in tensile, compressive, flexural and impact tests compared to the commonly employed raster orientations.

The energy absorption due to low-velocity impact on non-hybrid and hybrid (Kevlar-K, carbon-C, and glass-G) fabric reinforced epoxy composite laminates were studied by conducting standard drop weight tests. The experimental energy absorption results were compared with finite element analysis results. Both values were in good agreement with a maximum variation of about 6%. Kevlar/epoxy (K/K/K) specimen recorded the highest energy absorption (18.67 J) followed by Kevlar specimen sandwiched with glass fabric in the middle layer (K/G/K) (17.24 J). Specimens consisting of glass or carbon layers in the middle, sandwiched by Kevlar layers at the top and bottom (K/G/K and K/C/K) exhibited better energy absorption compared with laminates consisting of all three fabric reinforcements (K/C/G (13.38 J), G/C/K (16.11 J) and C/G/K (16.04 J), respectively). Considering the cost of these composite laminates, K/G/K composite offers 21% reduction in material cost when compared to K/K/K specimen and also offered reasonably enhanced impact resistance and energy absorption as compared to other hybrid composites. Hence, this data may be useful for developing cost effective impact resistant components for defense (protective helmets and body armor) and aerospace (aircraft body components) sectors. The morphologicalstudy of the drop weight impact tests revealed that, delamination, fiber breakage, fiber splitting, and matrix cracking are the major damage mechanisms observed in the study. The cost was found to be a critical factor to compare between the different composites. © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC

In this paper, the influence of E-glass fiber volume fraction and laying angle on the damping and strength of composite laminates was comprehensively analyzed. By increasing the fiber laying angle and reducing the glass fiber volume fraction, the damping capacity of the composite laminate was increased, but the tensile strength of the laminate was reduced; By reducing the fiber laying angle and increasing the glass fiber volume fraction, the tensile strength of the composite laminate was increased, but the damping characteristics of the laminate was reduced. In addition, in the damping experiment of composite laminates, in order to avoid the influence of external damping sources, the vacuum non-contact damping test method was adopted in this paper, and the influence of air damping on the damping experiment results of composite laminates was comparatively analyzed. The results of comparative experiments showed that air damping had a very obvious influence on the damping of composite laminates, especially when the damping of composite laminates was small, the influence of air damping would be greater.

Advanced composite laminates (i.e. glass composite laminates) are highly susceptible to low velocity impact, and the induced damage failures substantially reduced their residual mechanical properties and safe-service life during their application. Therefore, experiments and simulation efforts to predict their low-velocity impact damages and energy absorbing have significant importance in composite structures design. In this regards, experimental and finite element analysis (FEA) with aiding Abaqus software were respectively performed to investigate the influence of yarn hybridisation on the response of composite laminates under low velocity impact. The hybrid yarns, which consisted of S-glass and polypropylene yarns have been used to manufacture two types of composites; non-crimp cross-ply hybrid yarns and twill hybrid fabric composites. Additionally, for comparison, the non-crimp cross-ply and twill fabric composite laminates have been made from glass fibres only. The vacuum infusion resin process has been adopted to manufacture these composite laminates. The impact performance of composite laminates has been investigated using low-velocity impact at 15 J, 35, and 50 impact energy levels. The numerical analysis was executed using Abaqus/Explicit and Hashin failure criteria and continuum damage mechanics by using homogenous shell were adopted to simulate the intra-laminar damage in layers. Meanwhile, standard cohesive inter-laminar interfaces that inserted between composite layers with quadratic stress failure criteria have been used to model delamination failures. The numerical results regarding impact force-time, displacement–time and energy-time histories plots, as well as the damage evolution behaviour of matrix crack and fibre fracture, presented an agreement with experimental results.

Because of the excellent static and fatigue performance, the interference-fit bolted structure has a wide application prospect in the joint field. In this paper, an improved spring-mass stiffness analytical prediction model is established for the interference-fit bolted single-lap laminated composite structure. The influences of interference-fit percentage, bolt preload, secondary bending and interface frictions are considered in the model. Combined with experimental research, the value of secondary bending moment coefficient ε is studied, and the correctness of the analytical model is verified. Based on the improved stiffness model, parametric research and regression analysis on the interference-fit percentage, preload, friction, laminate width and material properties are carried out and show that the overall structure stiffness is obviously affected by ε value, laminate width and laminates properties. The stiffness decreases with the increase of ε and increases with the increase of laminate width. And as the key factors, the interference-fit percentage mainly affects the joint local friction and bolt shear stiffness, the preload and friction coefficient mainly affect the local friction, and the laminates sizes and properties directly affect the overall structural stiffness.

This work reports the design and fabrication of novel printed single-wall carbon nanotube (SWCNT) electrothermal Joule heating devices. The devices are directly deposited on unidirectional (UD) glass fiber (GF) fabrics. The GF-SWCNT Joule heaters were integrated during manufacturing as "system" plies in carbon fiber reinforced polymer (CFRP) composite laminates. Specific secondary functions were imparted on the composite laminate endowing thus a multifunctional character. The efficient out-of-oven curing (OOC) of a CFRP laminate was demonstrated using a sandwich configuration comprising top/bottom GF-SWCNT system plies. A total power consumption of ca. 10.5 kWh for the efficient polymerization of the thermoset matrix was required. Infrared thermography (IR-T) monitoring showed a uniform and stable temperature field before and after impregnation with epoxy resin. Quasi-static three-point bending and dynamic mechanical analysis (DMA) revealed a minor knock-down effect of the OOC-CFRP laminates properties compared to oven cured CFRPs, whereas the glass transition temperature (Tg) was almost identical. The OOC-CFRP laminates were efficient in providing additional functions such as deicing and self-sensing that are highly sought in the energy and transport sectors, i.e., wind turbine blades or aircraft wings. The novel modular design provides unique opportunities for large-area applications via multiple interconnected arrays of printed devices.

In this study, the single-objective and multi-objective optimizations of composite laminates with free-edge boundaries are presented. Bees algorithm (BA) is used to search for the optimal design. An analytical technique is utilized to calculate the edge effect stresses at the free boundaries of the laminates. For this purpose, two laminates are considered: a flawless laminate with free straight edges and a laminate with a hole. The two laminates are subjected to uni-axial and thermal loads. The design of optimal layup in single-objective optimization is based on maximizing the interlaminar strength of the laminates. The multi-objective optimization is formulated for maximizing the interlaminar strength, minimizing the weight and the total cost of the composite components. The optimization variables are considered to be the number of layers, stacking sequence, and the thickness of each layer. Moreover, to verify the performance of BA, the results are compared with those of particle swarm optimization (PSO) and those based on resulting from multi-objective optimization of Kursave (KUR) function. The results of this study show the effect of geometric conditions of free edges as well as the type of loading (mechanical and thermal) on the optimization of composite laminates.

Transverse cracking and delamination are two of the most common failure modes in cross-ply composite laminates. The initiation and combination of these two failure mechanisms lead to catastrophic f...

This study addressed to determine the flexural properties of hybrid composite laminates (HCAFRE) under the strain rate sensitivity. The hybrid composite laminate was formed as consecutive stacking of a sequence of plain woven carbon fiber reinforced epoxy (CFRE) and a plain-woven aramid fiber reinforced epoxy (AFRE) laminates. The flexural tests were carried out at four different strain rates (0.01, 0.11, 0.55, 1.1 s−1) to determine the strain rate sensitivity of the HCAFRE. Moreover, the strain rate sensitivity of CFRE and AFRE was also determined individually. The effect of different fiber orientations (0°, 45°, and 90°) on the flexural properties of the composite laminates were also investigated at the scope of this study. In numerical analysis, composite laminates (CFRE, AFRE, and HCAFRE) were constituted in LS-DYNA finite element program using the Cowper-Symonds material model (MAT 112) which includes strain rate dependency. Consequently, it was seen that the experimental and numerical results were indicated a similar tendency to each other. Therefore, it was understood that the Cowper-Symonds material model is suited for the flexural behavior model of composite laminates under different strain rates.

In the current study, the finite element approach has been used to investigate the effect of compression and tension types of nonlinear edge loads on the vibration and buckling performance of inter...

In this research, the effects of induced delamination on the variation of the mechanical properties of composite laminates subjected to bending loads are investigated using a micromechanical model. For this purpose, the variation of the mechanical properties of delaminated laminates is determined using stress analysis of damaged ply and classical laminate theory (CLT) relationships. Using the proposed model and CLT, the fracture toughness due to induced delamination formation is presented in cross-ply laminates. Subsequently, the variation of strain energy release rate (SERR) is calculated in terms of crack density using analytical and finite element models to detect dominant failure modes in different crack densities. The results are compared with those of matrix cracking propagation. The results obtained by the proposed analytical model are in good agreement with those obtained by existing numerical and experimental approaches. The proposed model can be utilized to predict induced delamination formation in composite laminates subjected to bending loads.

A new method combining three-dimensional digital image correlation (3D-DIC) with a novel numerical framework was proposed to evaluate the severity of wrinkles in composite laminates. In this numeri...

The work aims to study the assessment of delamination location in composite laminates using vibration measurement with a chaotic oscillator method. Delamination is a type of damage that commonly occurs in composite laminates, which can cause a severe degradation of their material properties. The traditional vibration-based methods can encounter difficulties in detecting and locating these delamination-type damages especially when the size of delamination is relatively small and there is a significant level of noise in its vibration measurement. With this particular consideration, a vibration-based method using a non-linear chaotic oscillator was used in this study due to its sensitivity to the change in vibration signal characteristics. A numerical model of composite laminates with delamination damage under harmonic excitation was developed and the vibration signal obtained from composite laminates was processed using the chaotic oscillator method. A feature named Lyapunov Exponent (LE) was used as a delamination damage index to describe the characteristics of the chaotic oscillator for cases with delamination at varying structural locations. The effects of delamination locations on the developed damage index were analyzed in this work. The results showed that there was a strong correlation between the delamination location and the LE feature, even for the case with a relatively high level of measurement noise. The results demonstrated the effectiveness of the method to identify delamination in composite laminates, which has also the potential to be used to detect other types of damages.

An electromagnetically transparent, structurally robust and environmentally resistant enclosure of radar antenna for ground based systems to modern avionics in military aircraft and missiles is called as radome. Radome materials are classified based on: (i) type of function - surface-based or flight-mode and (ii) speed of operation - subsonic, supersonic to hypersonic. The desired properties of these materials are low dielectric constant and low loss factor in addition to its capacity to withstand the high temperature of operation. Composite laminates of glass or aramid fibre reinforced polymeric resins are radome material candidates for applications in subsonic range. However, ceramics are the only viable option for military aerospace applications such as a fighter jet travelling at Mach 3 or an advanced hypersonic missile speeding up to Mach 5. This review outlines the hand-full of ceramic materials already in application as radome materials like high-purity-alumina, pyroceram, slip-cast-fused-silica, their processing technology, electromagnetic and mechanical properties, advantages and disadvantages with respect to advanced military vehicles. Use of silicon nitride based radome materials, that has exceptional mechanical strength and thermal stability up to 1400 °C is illustrated with respect to reaction bonded silicon nitride, hot pressed silicon nitride, silicon oxynitride, sialon and their composites. Design of new generation radome materials was conceptualized and discussed as applicable to silicon nitride and related ceramics, wherein incorporation of varied degree of porosity improves electromagnetic properties, simultaneously, maintaining the required mechanical strength. Multilayer and graded porosity and its influence on electromagnetic properties were briefly discussed. Si3N4 ceramics having controlled porosity leading to optimum electromagnetic and mechanical properties produced through systematic processing is proposed as the futuristic high temperature radome material for supersonic applications.

In the aviation and structural industries, the requirement of smooth holes is an important safety problem. Since holes are a part of the joints made with fasteners, they affect the fatigue strength of the structure. Therefore, it is necessary to be very selective in terms of cutting parameters and cutting tools, especially in drilling metal/composite or composite/metal stacked materials. In this context, cutting conditions in conventional machining methods should be optimized or novel machining methods should be applied. In this context, this study minimized the limitations in machining of carbon fiber-reinforced composite (CFRP)/Ti6Al4V alloy stack material and the delamination problem that occurs especially in composite laminates. For this purpose, cutting conditions have been optimized for each of CFRP/Ti6Al4V alloy material, depending on the thrust force (Fz), surface roughness (Ra), and delamination factor (Fd) obtained by preliminary tests. The drilling tests were performed at the cutting speed of 60 m/min, the feed rate of 0.05 mm/rev for CFRP material, the cutting speed of 15 m/min, and the feed rate 0.05 mm/rev for Ti6Al4V material. The novel method for this study is that the tool was kept in the air for 1 min after each 4 mm drilling of Ti6Al4V alloy to cool the tool during the rebounds to the safe approach distance. Finally, according to the optimized cutting parameters, Fz, Ra, and Fd were assessed to evaluate the performances of cutting tools in the drilling of CFRP/Ti6Al4V stacked material. According to the experimental results and images of the digital camera and SEM device, flank wear and cracking as the wear type in the U-WC tool; flank wear, cracking, and BUE as the wear type in the TiAlN-coated tools; and outer corner wear and coating removal in diamond-coated tools. Moreover, when the tool performance is evaluated according to the cutting tool tip angle, the highest amount of wear was seen in cutting tools with 140° point angle.

The quality of fiber weave material is highly affected by the fiber orientation. This characteristic becomes obviously when we compare the composite laminates materials in different orientations of the same braiding mode, which leads to the anisotropy of the material mechanical properties. In this work, we propose a concise and efficient method for measuring the fiber orientation on plain weave carbon fiber and 2-D carbon fiber braided composites with angles. Our image acquisition method is making use of the phenomenon that the carbon fiber material has strong light specular reflection, image fusion algorithm perfect the texture of reflective part. Using image processing and computational geometry techniques to calculate the orientation. The results calculated are efficiency for fiber orientations with a remarkably stability. The method was built pure carbon fiber weave, with some small parameters tuning, it can be effectively applied to most plain weave carbon fiber and 2-D carbon fiber braided composites with angles.

The interface adhesive properties and mechanical properties of shape memory alloy composites were experimentally investigated. The two diameters of shape memory alloy (SMA) wire were surface modified by sandpaper, acid corrosion and alkali corrosion. Pull-out tests of single fiber and tensile tests of composite laminates were carried out. The results show that SMA after acid corrosion is the most effective to improve interface adhesive properties. With the increase of SMA diameter, the contact area between the matrix and SMA increases, so the degree of interfacial bonding is more obvious. The mechanical properties of SMA-modified composite laminates polished by sandpaper have been fully improved. SMA plays a full role in tensile resistance as long as the interface adhesive strength is large enough. Scanning electron microscopy shows that the surface roughness of the SMA wire treated in H2SO4 is more obvious than the other two.

Fiber reinforced polymer composites are quickly gaining market share in structural applications, but further growth is limited by their lack of toughness. Fiber hybridization is a promising strategy to toughen composite materials. By combining two or more fiber types, these hybrid composites offer a better balance in mechanical properties than non-hybrid composites. This study presents the effect of different interlaminar hybridization and cutout sizes on the vibration and buckling characteristics of hybrid fiber metal laminates (HFMLs) subjected to partial edge loads by developing finite element formulation. Since the stress distribution within the plate element is highly non-uniform in nature, the dynamic approach has been used to solve the buckling problems wherein two sets of boundary conditions are used, one for pre-buckling stresses and other one for buckling load calculations. A 9-noded heterosis plate element has been used to discretize the plate by taking into account the effect of shear deformation and rotary inertia. The present study consists of aluminum metal face sheets bound with four layered symmetric hybrid cross-ply laminate schemes. In this scheme, six different hybrid combinations have been considered. The performance of each hybrid combination is investigated under various loading combinations. Further, the effect of different parameters such as boundary condition, cutout ratio, width and position of localized edge loads, plate aspect ratio, and hybrid configurations are included in this work. It is revealed from the study that the hybrid configurations under different cutouts significantly affect the vibration and buckling characteristics under different localized edge loads.

To tackle the challenges of insufficient heat conduction capacity and thermally/mechanically induced internal damages of glass fiber reinforced epoxy composite (that traditionally serves as circuit board substrate), hexagonal boron nitride (h-BN) was functionalized using natural flavonoid dihydromyricetin (DMY) and then compounded with reversible Diels–Alder (DA) bonds crosslinked epoxy and glass fiber cloth (GFC) reinforcement to fabricate self-healing thermally conductive glass fiber cloth reinforced epoxy (GFREP) composite by a facile two-step coating method. Particularly, the GFC was coated with the solution containing high concentration modified h-BN, and then impregnated with dip coating solution containing lower concentration h-BN. The gradient variation of modified h-BN concentration not only effectively reduced the interfacial heat resistance, but also avoided excessive deterioration of mechanical strength. The produced GFREP composite exhibited excellent in-plane (6.22 W m−1 K−1) and through-plane (1.53 W m−1 K−1) thermal conductivities at 35.0 wt% h-BN content. The reversible DA reaction helped to realize interlaminar crack healing of the composite as characterized by high degrees of recovery of mechanical strength (70 ~ 85%) and thermal conductivities (62 ~ 89%). Besides, the attenuated thermal conductivity caused by interfacial debonding between copper clad and the composite in the model copper clad laminates can also be restored via the same mechanism. Lastly, the composite laminates proved to be coupled with controlled degradability in good solvent so that they can be recycled. This study offered an efficient way to prolong the service life of thermally conductive GFREP composite for integrated circuit packaging applications. The reversible DA reaction at the crack interface proves to be able to recover the structural integrity, which pushes the physical reconnection of the separated h-BN micron sheets residing on the fractured surfaces at the same time and re-establishes the continuous phonon transfer pathways.