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The Failure Mechanism of 3D C/C Composite Under Compression-Shear Coupled Loads: An Experimental Study
Abstract
Material strength under complex stress states is vital for structure design. This paper studied the strength and failure behaviour of 3D C/C composites under compression-shear coupled loads. Experiments were conducted using a modified anti-symmetric four-point bending (MAFPB) method and off-axis compression method. Two dominant failure modes were observed; 1) shear and 2) compression. Mode transitions under relatively low shear/compressive rations were also observed. Results show that the material exhibits significantly lower failure stress under shear-compressive load compared to compressive or shear strengths alone. Further analysis revealed that meso-scale geometry characteristic including tow crimps and interfacial cracks are the main inducements: (1) tow crimps lead to local bending moment and increase local shear stress, (2) matrix-tow cracks formed under shear load degrade the lateral support of axial tows, (3) matrix fibre splitting and local buckling within tows induced by compressive load further reduce the shear strength of axial tows. Failure stresses in off-axis tests are lower compared to those in MAFPB tests due to the existence of bi-axial compression. These findings show that shear failure is a weakness for the 3D C/C composite and can provide insights for further material design and structural strength analysis.
... For the investigation of the strength of structures and design of materials, this understanding is important. Shear stress evaluation is vital for confirming durability and enhancing the standard of construction of composite structures by providing insight into their mechanical characteristics and failure processes [41][42][43]. ...
The excellent mechanical strength with low weight of polymer-based composites makes them superior over conventional materials like steel and aluminum in terms of mechanical properties. Nowadays, researchers are working to develop natural fiber-based sustainable composite. Glass fiber, when combined with jute fiber, could greatly enhance the mechanical characteristics of composites; the sequence of the layers mostly determines these properties. In this study, the hybrid laminate of jute and glass fiber with resin polyester is developed with The representative volume element utilized in ANSYS. In ANSYS material design module, the 3D microstructure of composite material is created with various fiber volume fractions of glass fiber and jute fiber. After that, the effective elastic properties of hybrid jute/glass fiber and polyester as matrix, glass fiber/polyester, and jute fiber/polyester are evaluated and the simulation-based effective elastic property is validated by existing experiment value which showed good agreement. For further study, in Ansys ACP PrepPost, the composite laminate such as hybrid jute+glass fiber/polyester, glass fiber/polyester, and jute fiber/polyester is created with desired lamina thickness, stacking sequence, and fiber orientation. Thereafter, it was transferred to a static structure module to perform tensile and bending test analysis. Ansys ACP post-processing is utilized to investigate stress induced at each lamina of the composite specimen. This study revealed that by adding glass fiber to natural fiber, the mechanical performance is enhanced significantly, whereas hybrid jute+glass fiber/polyester (S2) demonstrated the highest tensile strength 259MPa compared to other hybrid laminate composites. Astonishingly, The hybrid composite jute+glass/polyester (S2) exhibited 10% higher bending strength than glass fiber/polyester (S1) and 64% more than net jute fiber/polyester (S5). Additionally, S2 demonstrated 9.5% higher shear strength compared to S1 and 64% more than S5. This study will give a great understanding of how adding glass fiber to jute fiber, could enhance the mechanical properties, which will contribute to the design of an efficient composite part for automotive such as car interiors, car doors, trim panels, lightweight applications, and packaging industries.
In underground rock engineering, the surrounding rock often experiences a mixed compression–shear state. To investigate the mechanical properties and failure modes of in-situ rocks under varying compression–shear ratios, this study employed an acoustic emission (AE) monitoring system and digital image correlation (DIC) technology to analyze cylindrical rock (CY) and cubic rock (CU). A series of variable-angle shear tests (VASTs) were conducted by adjusting the mold angle. The experimental results demonstrate that the peak load (Ps) for both types of rocks exhibited a negative correlation with the shear angle (α); specifically, CU exhibit 60%-90% higher Ps compared to CY at same α. The cohesive strength (c) calculated from VASTs-CY was lower than that from VASTs-CU, while the internal friction angle (ϕ) was higher, but when α ≥ 60°, the c and ϕ of CY and CU were nearly equal, which was accurate for engineering design. Meanwhile, the expression of the dividing line of the tension–shear crack was proposed by a novel approach that integrates AE parameters, clustering concepts, and genetic algorithms. Based on changes in AE hit rate, both types of rocks exhibited high similarity in their failure processes, displaying significant segmented variations. CY exhibited more active AE activity than CU. As the pressure–shear ratio decreased, local rock damage occurred more easily with greater degrees of damage and less smooth fracture surfaces.
Out-of-plane compression experiments with the strain rate from 0.0001/s to 1000/s are performed on 3D fine weave pierced Carbon/Carbon (C/C) composite using a universal testing machine, a high-speed testing machine, and a split Hopkinson pressure bar (SHPB). The compressive failure mechanism of the composite is analyzed by multi-scale analysis method, which ranges from micro-scale defect propagation, through meso-scale microstructure failure, to macro-scale material failure. In order to predict the out-of-plane compressive properties of 3D fine weave pierced C/C composite at different strain rates, a strain-rate-dependent compressive constitutive model is proposed. The results show that the out-of-plane compressive behavior of the 3D fine weave pierced C/C composite is sensitive to strain rate. With increasing the strain rate, the initial compressive modulus, the maximum stress and the strain at the maximum stress increase. The difference in mechanical behavior between quasi-static and high strain rate compression is owing to the strain rate effect on the defect propagation of the 3D fine weave pierced C/C composite. The proposed constitutive model matches well with the experimental data.
The applicability and limitation of several quadratic strength theories were investigated with respect to 2D-C/SiC and 2.5D-C/SiC composites. A kind of damage-based failure criterion, referred to as D-criterion, is proposed for nonlinear ceramic composites. Meanwhile, the newly developed criterion is preliminarily validated under tension-shear combined loadings. The prediction shows that the failure envelope given by D-criterion is lower than that from Tsai-Hill and Hoffman criteria. This reveals that the damage-based criterion is reasonable for evaluation of damage-dominated failure strength.
We review the development of virtual tests for high-temperature ceramic matrix composites with textile reinforcement. Success hinges on understanding the relationship between the microstructure of continuous-fiber composites, including its stochastic variability, and the evolution of damage events leading to failure. The virtual tests combine advanced experiments and theories to address physical, mathematical, and engineering aspects of material definition and failure prediction. Key new experiments include surface image correlation methods and synchrotron-based, micrometer-resolution 3D imaging, both executed at temperatures exceeding 1,500 degrees C. Computational methods include new probabilistic algorithms for generating stochastic virtual specimens, as well as a new augmented finite element method that deals efficiently with arbitrary systems of crack initiation, bifurcation, and coalescence in heterogeneous materials. Conceptual advances include the use of topology to characterize stochastic microstructures. We discuss the challenge of predicting the probability of an extreme failure event in a computationally tractable manner while retaining the necessary physical detail.
In this work, interlaminar tensile (ILT) strengths and microscopic failure mechanisms of 3D needled C/C composites were studied at ultra-high temperatures (up to 2800 °C). Experiments were conducted using the V-shaped notched specimen compression method. The measured ILT strengths compared favorably to results obtained via flatwise tension and diametral compression tests. In addition, the high-temperature transverse displacement field was measured using digital image correlation and the temperature field was measured using an infrared thermal imager. The transverse displacement and temperature fields were uniform in the gage section. The results confirm the effectiveness of this method for measurements of 3D needled C/C composites. The ILT strengths of the 3D needled C/C composites were measured at 1200 °C, 1600 °C, 1800 °C, 2000 °C, 2400 °C, and 2800 °C. The ILT strengths increased with the temperature up to 1600 °C, and then decreased in the 1600–2800 °C range. The failure mechanisms were investigated via optical microscopy. The needling fibers were pulled out, which indicates that the ILT strengths were primarily dependent on interfacial strength. It is intended that these results will provide some practical guidelines for ultra-high temperature engineering applications.
3D needled C/C-SiC composites show scattered mechanical properties in the experimental tests due to the random needling region distributions in the composites and the variability of microstructures at the needling regions. A specified methodology is developed to predict the scattered mechanical properties of the composites. Meso-scale models of the test specimens are established, in which the random distribution of needling regions and the uncertain properties of needling regions are considered. The predicted coefficients of variation for initial modulus, strength and failure strains of the composite agree well with the experimental results. Size effect of the test specimens on the experimental results is well analyzed by the proposed method. The influence of needling density, depth and distribution on the uncertainty of composite properties are also obtained. The methodology introduced by this work would guide the design of the proper specimen size and manufacturing needled materials with lower scattered mechanical properties.
Carbon fiber-reinforced carbon matrix (C/C) composites are attractive alternative materials for the fabrication of various high-temperature structural components subjected to complex loading conditions. A modified anti-symmetric four-point bending (MAFPB) method for testing a V-notched beam specimen was developed in this study for the investigation of the mechanical behavior of C/C composites under biaxial shear and compression. A finite element model of the specimen was generated to examine the effects of the notch radius and notch spacing on the uniformity and distribution of the stresses in the gauge area. Uniform shear and normal stress were observed in the gauge section of a specimen with a blunted notch and appropriate notch spacing. The three-dimensional (3D) mechanical behaviors of a C/C composite determined by MAFPB tests under pure shear and various biaxial shear–compression stress states were compared with those determined by Iosipescu and off-axis compression experiments. The MAFPB test was found to produce reliable estimates of the mechanical behaviors and failure mechanisms of C/C composites under a wide range of biaxial shear–compression stress states. The shear fracture stress of a 3D C/C composite was particularly observed to significantly decrease with increasing compressive stress component.
This paper investigates the failure behavior of three-dimensional (3D) braided composites subjected to biaxial tension and compression through an improved micromechanical computational method and the finite element (FE) method. The yarns and the out-of-yarn matrix in the composites are modeled by an extended Hashin criterion and an extended Drucker-Prager criterion, respectively. The uniaxial mechanical properties are analyzed based on the available experimental data as a verification of the models. The biaxial progressive damage and failure behavior are investigated using the models. The braiding structure, whose diversity results in the difference in failure modes during damage evolution, has significant influence on the biaxial failure correlation of the composites. The predicting formulae for failure envelopes are suggested in this study. The failure envelopes of 3D four-directional and five-directional braided composites can be described by quadratic tensor theories, and the envelopes of 3D six-directional and seven-directional braided composites can be predicted by the maximum strain criterion.
The effects of complex state of stress on the compressive behaviour of 3D carbon/carbon composites are investigated by application of uniaxial and biaxial loadings using a specially developed Zwick cruciform testing facility. The shape of the biaxially loaded cruciform specimen is optimised to avoid premature fracture outside the gauge section. A semi-analytical method is proposed to determine the stress components in the gauge section of the biaxial specimen. The experimentally obtained failure stress relation, which traces an elliptical path in the principal stress space, can be well represented by the Tsai criterion with a stress interaction parameter of F12=-0.85. Macro-fracture morphology and SEM micrographs are examined and the results show that the failure mechanisms of the composites vary with the loading ratio. The results also suggest that the biaxial stress interaction effect is represented by a domain in the biaxial specimen, which is characterised by torsion and bending fractures in the dislocated fibres between two adjacent Z yarns.
Unidirectional carbon fiber composites were tested under multi-axial loading conditions including tensile/compression/shear loadings along and perpendicular to fiber directions. Compression dominated tests showed brittle fracture mode like local kicking/buckling, while tension dominated tests showed fracture mode like delamination and fiber breakage. Pure shear tests with displacement control showed material hardening and softening before total failure. Tsai-Wu failure criterion with Mises-Hencky interaction term was used as the yield criterion, and an associated flow rule (AFR) was used to describe the plastic flow of this material. The modified Tsai-Wu failure criterion was able to predict the failure of the composites under different loading conditions. A new material post-failure softening rule was proposed, where a new parameter was introduced to represent different loading conditions of the composite. This model was implemented to ABAQUS/Explicit as a user material subroutine (VUMAT). Numerical simulations using finite element method well duplicated the elasticity and plasticity of this material. Failure features like delamination was simulated using cohesive surface feature. This model showed good capacity in predicting both failure initiations and fracture modes for the unidirectional fiber composites. This model has good application potentials to large-scale engineering problems.
This paper established a combined elastoplastic damage model to analyze the nonlinear mechanical behavior of 3D needled C/C-SiC composites. Inelastic deformation and stiffness degradation of the composite were characterized by the plasticity and damage theories. An innovative plastic potential function containing variable parameters was proposed to consider particularly the anisotropy of plastic deformation in each material direction. Based on the Weibull statistical distribution of the material strength, an exponential damage state function was established to characterize stiffness degradation for the composite in each material direction. Parameters of this constitutive model were determined from experiments data. It can be found that the nonlinear stress-strain curves for the composite under off-axis tensile and shear loadings can be accurately described by the model. The yield and damage surfaces of the composite were also studied. Finally, the constitutive model was validated by analyzing the mechanical behavior of a composite plate containing a center-hole subjected to tensile load.
This paper focuses on the design of the appropriate geometry for cruciform coupons conceived to be tested under tensile biaxial transverse loads. To this end, Finite Element models were developed and their results were used to propose a geometry which minimizes undesirable effects such as stress concentrations, develops a uniform state of biaxial stresses in the central zone of the coupon and assures that the failure takes place at this zone. The experimental results confirm the validity of the numerical models.
This paper focuses on the mechanical characterization of biaxial braided composites under multiaxial stress states. Off-axis experiments in tension and compression were used to introduce multiaxial stresses in the material. The characterization was focused on nonlinear deformation and failure behavior: loading/unloading of the specimen was used to identify the mechanisms for nonlinear deformation and a high-speed-camera is used to record the failure mode of the specimen. It has been found that the failure modes are mainly dominated by shear-induced transverse cracking. A dependency of the failure mode on the transverse yarn stress was observed. The deformation was strongly nonlinear, and dominated by the shear-behavior of the yarns. An equivalent laminate model was employed for failure prediction, showing that the failure of the biaxial braided composites can be predicted accurately, when the knockdown induced by yarn waviness is considered in the material input parameters.
A coupled fluid/thermal/ablation analysis for a carbon/carbon composite leading edge in hypersonic reentry environments was conducted. A finite rate surface ablation model for carbon materials was incorporated into the aerothermodynamics computational fluid dynamics code to simulate the nonequilibrium gas–surface interactions, and then the computational fluid dynamics solver was coupled with a thermal analysis, finite element method solver. The gas and solid regions were coupled at the surface by appropriate energy and mass balances. A mesh movement algorithm was implemented in the finite element method to achieve surface recession. The capabilities of this coupled method were demonstrated by simulating the thermal and ablation behaviors of a wedge-shaped leading edge in hypersonic flows. The effect of the nose shape change on the ablation process was also discussed. The coupling method developed in this work could be used to simulate aerothermodynamics and carbon ablation during Earth reentry.
The initial stress concentration resulting from the needle-punching effect is a fundamental issue in the longitudinal strength model for laminated carbon/carbon composites. In the present work, this stress distribution is obtained by combining the finite difference method with the shear-lag model. The effect of the needled hole size on the stress concentration is investigated. The broken width is more significant than the separated length for the improvement of the stress concentration degree. The increase of the fiber volume fraction is shown to decrease the overload area. Random needling distributions are compared to the ordered one. Few interactions of each needled area are found in the ordered distribution and the stress concentration is decreased in these random needling distributions. Finally it is concluded that the enlarging of each needled hole, especially the accumulation of broken fibers, during the cyclic process of overlaying laminates and punching is the prime reason for tensile strength reduction under the condition of high needling density.
This paper proposes a new constitutive model named general weighted flexibility matrix (GWFMM) material model for the analysis of structures made of bi-modulus orthotropic material in complex three-dimensional stress state. The material properties of the GWFMM model are assigned according to the positive–negative signs and magnitudes of the principal material stresses. General analysis modules of the orthotropic materials with different moduli of elasticity in tension and compression are developed. Comparing with Bert’s model for laminated materials, GWFMM model can obtain more accurate mechanical response of structures in complex three-dimensional stress states.
In this paper, aluminum hexagonal honeycombs are experimentally studied for their mechanical behavior under combined compression-shear loads. Quasi-static and dynamic tests were conducted at five different loading velocities ranging from 5 × 10-5 ms-1 to 5 ms-1 using MTS and INSTRON machines, among which tests at 0.5 ms-1 and 5 ms-1 were conducted for the first time. Specially designed fixtures were employed to apply combined compression-shear loads to honeycombs at angles of 15°, 30° and 45° respectively. Three types of HEXCELL® 5052-H39 aluminum alloy honeycombs with different cell sizes and wall thicknesses were crushed in two different plane orientations (TL and TW). The deformation, crushing force, plateau stress and energy absorption of aluminum honeycombs are presented. The effects of loading plane, loading angle and loading velocity are discussed. An empirical formula is proposed to describe the relationship between plateau stress and loading angle.
In-plane tensile experiments for 3D needled C/C–SiC composites were conducted from room temperature to 2000 °C to study the tensile behavior and microscopic failure mechanisms. Results show that the tensile strength, toughness and failure strain increase with the increase of temperature, while the modulus decreases. The tensile strength increases gradually from 98.7 to 162.6 MPa at 1800 °C and then decreases to 154.3 MPa at 2000 °C. At elevated temperatures, a large amount of fibers are pulled out, and the fracture surfaces show jagged patterns, which indicates that the interfacial strength decreases with the increase of temperature. The weak interface can induce the lower tensile modulus, and can improve the tensile strength of the C/C–SiC composites. At high temperature, the weak interfacial strength can be attributed to the release of thermal residual stress and graphitization of pyrolytic carbon.
The damage coupling effects of a two-dimensional carbon fibre-reinforced silicon carbide composite (2D-C/SiC) under proportional loading conditions were investigated using off-axial tensile and compressive tests. The applied load was translated into three proportional stress components in the fibre bundle directions of the composite. The tensile, compressive and shear stress-strain behaviours of the composite in the axial directions were obtained and analysed by mounting strain gauges on the tested specimens. Based on the stress-strain behaviours of the composite subjected to a single axial load, the coupling effects between damage caused by different stress components were characterised and analysed based on the strain deviations. Finally, SEM (scanning electron microscope) techniques were used to identify the damage mechanisms and failure modes of the tested specimens. The micro-damage model was built to explain the damage coupling effects of the composite. In addition, the influences of the damage coupling effects on the mechanical properties of the material were obtained.
Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon (C/C) using isothermal chemical vapor infiltration (CVI). The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.
The compressive experiments on the 3D braided composites with different braiding parameters are performed in three directions (longitudinal, in-plane and transverse) at room and liquid nitrogen temperature (low as -196 degrees C). Macro-Fracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the stress-strain curves and the compression properties are significantly different in the longitudinal, in-plane and transverse direction. Meanwhile, the compression properties at liquid nitrogen temperature are improved significantly than that at room temperature. Moreover, the damage and failure patterns of composites vary with the loading directions and test temperature. At liquid nitrogen temperature, the brittle failure feature becomes more obvious and the interfacial adhesion capacity is enhanced significantly. In addition, the compressive properties and failure mechanism at room and liquid nitrogen temperature can be significantly affected by the braiding angle and the fiber volume fraction.
The strain rate dependent mechanical behaviour was studied for the common out-of-autoclave aerospace textile composite 5-harness-satin carbon-epoxy. End-loaded and off-axis and compression tests were carried out at three different strain rate levels ( and ) to determine the effect of strain rate for transverse compression and combined transverse compression/in-plane shear loading. The dynamic tests were carried out on a split-Hopkinson pressure bar, where high speed photography and digital image correlation allowed a detailed study of the specimen deformation and failure process. Quasi-static reference tests were carried out on an electro-mechanical test machine using the same specimen type and a static DIC system. Pronounced strain rate effects on the axial stress-strain response were observed for all specimen types. Failure envelopes for the combined stress state were derived from the experimental data and compared with the maximum stress criterion, which appears well suited to approximate the experimental failure envelope at all strain rate levels. It was observed that the failure envelope was simply scaled up with increasing strain rate, while the overall shape was found to be strain rate independent.
This work examines the responses of three-dimensional carbon/carbon composites under axial compression and transverse shear. By using a 3D weaving technique, two types of preforms with different bundle sizes of the weaving yarns were prepared for assessing its influence on the failure behavior. Carbon yarns were arranged in a three-axis, orthogonal form with interlacing loops on outer surfaces. The carbon matrix was added by using a phenolic resin as the matrix precursor. Resin transfer molding was used for resin impregnation, followed by the curing and carbonization of the resin. The matrix filling was repeated up to five cycles, and the efficiency of the matrix filling was examined. Special fixtures were designed for applying the loads to the 3D composites. Microscopic observations on the induced damage were carried out. The axial yarns were found to undergo bending fracture in the compressive tests. The yarn imperfection, rather than the fiber misalignment, was the major failure-determining factor. The bending of the yarns is analyzed, and the critical value of imperfection that leads to bending fracture is given. The transverse shear resulted in complex but intriguing damage modes, which are closely related to the surface loops and through-thickness yarns. Some keys for preform design to best withstanding the shear are discussed.
The effect of a superimposed shear stress on the axial compressive strength of aligned fiber composites is investigated through a combination of experiments and analysis. Experiments were conducted on flat coupons using a custom biaxial testing facility. Shear and compression were found to interact strongly. The interaction failure envelope follows approximately a linear trend along the line joining the critical stress at zero shear on one axis and the shear strength on the other. The 2-D and 3-D micromechanical models used previously to predict the compressive strength are modified to include the shear. In the models the composite has a sinusoidal imperfection which is uniform across the microsection width. The imperfection characteristics are chosen so that the calculated critical stress at zero shear corresponds to the measured strength. The models are shown to capture well the interaction between shear and compression. Calculated failure envelopes are in good agreement with the experimental results. For all combinations of shear and compression considered, deformation localizes into a narrow band of highly bent fibers after the critical state. The band initially is normal to the axial load but broadens and rotates as the solution is followed deeper into the postfailure regime as it did for pure compression. Important aspects of proper testing and modeling are discussed, and recommendations are given for design including a critical review of a simpler model in which the fibers do not deform.
The influence of compression and shear loads on the strength of composite laminates with z-pins is evaluated parametrically using a 2D Finite Element Code (FLASH) based on Cosserat couple stress theory. Meshes were generated for three unique combinations of z-pin diameter and density. A laminated plate theory analysis was performed on several layups to determine the bi-axial stresses in the zero degree plies. These stresses, in turn, were used to determine the magnitude of the relative load steps prescribed in the FLASH analyses. Results indicated that increasing pin density was more detrimental to in-plane compression strength than increasing pin diameter. Compression strengths of lamina without z-pins agreed well with a closed form expression derived by Budiansky and Fleck. FLASH results for lamina with z-pins were consistent with the closed form results, and FLASH results without z-pins, if the initial fiber waviness due to z-pin insertion was added to the fiber waviness in the material to yield a total misalignment. Addition of 10% shear to the compression loading significantly reduced the lamina strength compared to pure compression loading. Addition of 50% shear to the compression indicated shear yielding rather than kink band formation as the likely failure mode. Two different stiffener reinforced skin configurations with z-pins, one quasi-isotropic and one orthotropic, were also analyzed. Six unique loading cases ranging from pure compression to compression plus 50% shear were analyzed assuming material fiber waviness misalignment angles of 0, 1, and 2°. Compression strength decreased with increased shear loading for both configurations, with the quasi-isotropic configuration yielding lower strengths than the orthotropic configuration.
Meso-scale (unit cell of an impregnated textile reinforcement) finite element (FE) modelling of textile composites is a powerful tool for homogenisation of mechanical properties, study of stress–strain fields inside the unit cell, determination of damage initiation conditions and sites and simulation of damage development and associated deterioration of the homogenised mechanical properties of the composite. Meso-FE can be considered as a part of the micro-meso–macro multi-level modelling process, with micro-models (fibres in the matrix) providing material properties for homogenised impregnated yarns and fibrous plies, and macro-model (structural analysis) using results of meso-homogenisation. The paper discusses stages of the meso-FE analysis and proposes a succession of steps (“road map”) and the corresponding algorithms for it: (1) Building a model of internal geometry of the reinforcement; (2) Transferring the geometry into a volume description (“solid” CAD-model); (3) Preparation for meshing: correction of the interpenetration of volumes of yarns in the solid model and providing space for the thin matrix layers between the yarns; (4) Meshing; (5) Assigning local material properties of the impregnated yarns and the matrix; (6) Definition of the minimum possible unit cell using symmetry of the reinforcement and assigning periodic boundary conditions; (7) Homogenisation procedure; (8) Damage initiation criteria; (9) Damage propagation modelling. The “road map” is illustrated by examples of meso-FE analysis of woven and braided composites.
A review of experimental data and elementary theoretical formulas for compressive failure of polymer matrix fibre composites indicates that the dominant failure mode is by plastic kinking. Initial local fibre misalignment plays a central role in the plastic kinking process. Theoretical analyses and numerical results for compressive kinking are presented, encompassing effects of strain-hardening, kink inclination, and applied shear stress. The assumption of rigid fibres is assessed critically, and the legitimacy of its use for polymer matrix composites is established.
Various strengths of carbon–carbon composites (C/Cs) are comprehensively reviewed. The topics reviewed include tensile, shear, compressive, and fatigue strength as well as fiber/matrix interfacial strength of C/Cs. When data are available, high temperature properties, including creep behavior, are presented. Since C/Cs have extremely low fiber/matrix interfacial strength τd, the interfacial fracture plays important roles in all of the fracture processes dealt in this review. The low τd was found to divide tensile fracture units into small bundles, to seriously degrade both shear and compressive strength, and to improve fatigue performance. In spite of the importance of the interfacial strength of C/Cs, techniques for its evaluation and analysis are still in a primitive stage.