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The mechanical properties of metal matrix fiber-reinforced composites depend on many aspects of their structure in a complicated way. In this paper, we propose a phase-field-cohesive-zone framework to study interface debonding, matrix cracking, and their competition in metal matrix fiber-reinforced elastoplastic composites by numerical simulation. This approach combines an explicit cohesive zone model for interface debonding and a phase field model for matrix cracking. The features of this framework are: (1) crack propagation and branching can be simulated without the need to track the cracks; (2) the interface debonding is described by the cohesive zone model, and is not directly interfered by the phase field in the bulk; (3) the cohesive interface has zero thickness instead of being regularized; (4) any reasonable cohesive law of interest is readily incorporated with very few constraints; (5) the competition of the two failure mechanisms, namely, matrix cracking and interface debonding, is captured. Accuracy of this framework is verified with existing analytical and numerical results. The proposed framework shows a potential in investigating various complicated crack behaviors in composites. [ABSTRACT FROM AUTHOR]

When ceramic-matrix composites (CMCs) are under tension-tension cyclic fatigue loading, stochastic matrix cracking evolves with applied cycles and the closure of cracks occurs upon unloading. Evolution, opening, and closure of matrix cracking affect the reliability and safety of CMC components during operation. The objective of this paper is to establish the relationship between the hysteresis loops, cracking evolution, opening, and closure based on a new hysteresis constitutive model. Multiple micro damage parameters, e.g., unloading/reloading inverse tangent modulus (UITM/RITM), interface reverse slip ratio (IRSR), and interface new slip ratio (INSR), are developed to characterize the hysteresis loops with cracking evolution and closure. Upon unloading, the closure of matrix cracking decreases the UITMs and IRSR of the tension-tension fatigue hysteresis loops; upon reloading, the opening of matrix cracking increases the RITMs and IRSR of the tension-tension fatigue hysteresis loops. Experimental tension-tension fatigue hysteresis loops in different CMCs are predicted for different peak stresses and cycles. Effects of fiber volume, interface properties, peak stress, and stress ratio on ITM, IRSR, and IRSR are discussed. The developed approach can be used for cracking evolution, opening, and closure identification in CMCs. [ABSTRACT FROM AUTHOR]

In this paper, the damage and fracture in unidirectional and cross-ply prepreg melt-infiltration (MI) Cansas-3203™ SiC/SiC composites were investigated by monotonic and cyclic loading/unloading tensile and acoustic emission (AE) in situ monitoring. Based on the analysis of AE signals under cyclic loading/unloading tensile, the monotonic tensile stress–strain curves in SiC/SiC composites were divided into three main stages, and the corresponding stress and strain domains were determined. A micromechanical damage-based constitutive relationship was developed for predicting the tensile nonlinear compliance curves and hysteresis loops. Multiple micro damage parameters, e.g., interface debonding ratio (IDR), fibers broken fraction (FBF), inverse tangent modulus (ITMs), and interface slip ratio (ISR), were adopted to characterize tensile damage evolution. The associations of composite's tensile nonlinear behavior, cyclic compliance hysteresis loops, and internal damage evolution with the fracture were established. Experimental tensile curves, internal damage evolution, and hysteresis loops were predicted utilizing the developed micromechanical damage-based constitutive relationship. Compared with cross-ply SiC/SiC composite, the tensile peak stress corresponding to AE signal occurrence was much higher for unidirectional SiC/SiC composite. Approaching composite's proportional limit stress (PLS), the AE signals of both unidirectional and cross-ply composites were increased rapidly, indicating a rapid increase in matrix cracking. Upon reloading, there was no AE signal at the initial stage of reloading; however, with increasing tensile stress, AE signals gradually occurred, and high AE energy signals appeared only with tensile stress exceeding the previous peak level. [ABSTRACT FROM AUTHOR]

To conveniently and feasibly characterize the interface debonding in particle-reinforced nonlinear viscoelastic polymer composites (PRNVPCs), a micromechanical model is proposed based on a normalization method that can convert the rate-dependent constitutive relationship of a nonlinear viscoelastic matrix into a rate-independent linear viscoelastic constitutive relationship. With this treatment, a linear homogenization scheme is used to achieve closed-form solutions for the critical particle stress and the critical time at the initiation of interface debonding in PRNVPCs. The change in the particle debonding stress versus the debonding angle is theoretically predicted with the new model, and the predicted change is qualitatively consistent with the experimental data. Furthermore, it is found that the particle debonding stress increases monotonically with decreasing particle size. The increase of the applied strain rate leads to an increase of the particle debonding stress but a decrease in the critical debonding time. This demonstrates that a smaller particle and a higher loading rate are both beneficial for improving the interfacial adhesion, while the latter will shorten the time needed to initiate interface debonding. The present research provides a convenient approach to theoretically characterize the interface debonding in PRNVPCs, which should be of guiding value for the design of advanced polymeric composites with a good load bearing capacity. [ABSTRACT FROM AUTHOR]

An analytical approach is established to analyze the mechanical behavior of a unidirectional (UD) composite subjected to an in-plane shear. The effects of the interface debonding on the in-plane shear strength and plasticity of the composite are evaluated respectively. The volume-averaged internal stresses of the fiber and matrix are calculated through Bridging Model. Owing to the stress fluctuation in the matrix caused by other phases (such as the imbedded fiber and interface crack), the homogenized matrix stresses must be converted into true values based on a stress concentration factor (SCF). A new in-plane shear SCF of a composite with debonded interface is derived and applied to the predictions of strain and strength in this paper. Moreover, the contribution of the relative slippage between fiber and matrix to the non-linear shear deformation of the composite is analyzed. Finally, the efficiency and accuracy of our theory are verified with a series of examples. The approach is very efficient because the calculation can be achieved with explicit expressions mainly based on the constituent material properties. The comparisons between predicted strength and deformation with the experimental results show that our analytical approach can give out reliable underlying data for multi-scale analysis. Moreover, this theoretical method can tell if and how much the interface of a composite needs to be modified for a given load environment. [ABSTRACT FROM AUTHOR]

In this paper, stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) subjected to different stochastic loading spectrums at intermediate temperatures (600 to 1000 °C) is investigated. Under stress rupture at stress level higher than the first matrix cracking stress, multiple damage mechanisms of matrix cracking, fiber/matrix interface debonding, interphase and fiber oxidation, and fiber fracture are considered to analyze evolution of composite strain. Four different stochastic loading spectrums are considered in the analysis of damage evolution and lifetime of fiber-reinforced CMCs under stress rupture loading. Relationships between stochastic loading stress, frequency, time, interface debonding and oxidation length, fiber failure probability, and stress rupture lifetime are established. Effects of stochastic loading stress and time, fiber volume, matrix crack spacing, interface debonding energy, interface shear stress, and temperature on composite strain, interface debonding and oxidation length, and the fiber failure probability versus time are analyzed. Experimental stress rupture strain and lifetime of SiC/SiC composite under constant stress and stochastic loading spectrums are predicted. When the stochastic loading stress, frequency, and temperature increase, the stress rupture lifetime and the time for the interface complete debonding and oxidation all decrease. [ABSTRACT FROM AUTHOR]

In this work, plaster molds for investment casting, reinforced with short polypropylene fibers, were prepared and their properties and fracture surface features were investigated. Fiber contents ranging from 0.10 to 0.50 wt% were introduced into a powder mixture of gypsum and mullite (ratio of 3:7) as reinforcements in order to prepare thin-walled plaster molds with high strength and permeability. The strength of green and fired plaster mold specimens was tested, the permeability was also tested, and their fracture surfaces were observed by scanning electron microscopy (SEM). The results show that the strength of the molds increases initially and then decreases with increasing fiber content. The green flexural strength of the specimens containing 0.20 wt% polypropylene fibers reached the maximum, c.a. 1.94 MPa, increased by 36.6%, and particularly, there was a slight increase in their fired strength, a maximum value of 0.45 MPa, in comparison with the fiber-free specimen. This low increase in the fired strength the reinforced specimen will produce a favorable effect on the collapsibility of shells in the casting cleaning process. In addition, the fired permeability of fiber-reinforced fired specimens exhibited significant enhancement, compared to that of the unreinforced ones. With increasing fiber content, the permeability of specimens increased from 8.6 to 11.5%. The improvement of green permeability was limited substantially. SEM observations indicate that the failure of the green specimens is a result of brittle fracture of the plaster substrate and/or fiber debonding from the matrix during loading. On the contrary, in fired specimens, the failure occurs by holes in the plaster substrate resulted from fiber ablation in the matrix during the firing process. The arrangement of polypropylene fibers can also affect the fracture behavior of molds. This proposed approach can reduce mold thickness without loss of strength and provide defined judgment basis for fracture features. [ABSTRACT FROM AUTHOR]

In this paper, the effect of pre-fatigue loading on tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using a micromechanical approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with applied cycles due to the damage mechanism of the interface wear. The micro stress field of the damaged composite including matrix cracking, fiber/matrix interface debonding, and fiber failure is obtained for the fiber and the matrix axial stress and the fiber/matrix interface shear stress in the interface wear region, interface debonding region, and the interface bonding region, respectively. The fracture mechanics approach, stochastic matrix cracking model, and global load sharing (GLS) criterion are used to determine the interface debonding length, matrix cracking density, and fiber failure probability at higher applied stress level considering the damage mechanism of the interface wear. The effects of fiber volume, matrix cracking, fiber/matrix interface shear stress, fiber strength, pre-fatigue peak stress, and number of cycles on pre-fatigue tensile damage and fracture of SiC/SiC composites are analyzed. The experimental tensile damage and fracture of SiC/SiC composites with and without pre-fatigue loading are predicted for different interface properties. [ABSTRACT FROM AUTHOR]

The paper focuses on the debonding between a cement-based overlay and a concrete substrate under a mechanical loading. Two categories of substrate surface preparation were considered: Sawing the Substrate and Sand Blasting of the casting surface of the substrate. Untreated substrate surface used in its original state was taken as the Reference Surface. The overlay material investigated was a cement-based mortar. Direct tensile tests perpendicular to the overlay-substrate interface were carried out at the age of 28 days and the results (tensile strength, residual post peak behavior) are presented and discussed. Attention was paid to the Sand Blasted surface which is a more realistic model of practical field conditions. The debonding propagation under monotonic and fatigue loading was monitored for sand blasted surfaces using the Digital Image Correlation technique. Results indicate that both surface preparation technique has its own efficiency level and gives different roughness. Among the techniques used, greater bond strength improvement was observed with the sawn substrate surface than with the sandblasted one. Moreover, under cyclic loading, major debonding along the interface occurs from the first cycle to the 20000th cycle and is negligible thereafter. [ABSTRACT FROM AUTHOR]

In this paper, the matrix multi-fracture of SiC/SiC ceramic-matrix composites (CMCs) is investigated using the critical matrix strain energy (CMSE) criterion. The BHE shear-lag model is used to analyze the micro-stress field of the damaged composite, and the fracture mechanics method and the CMSE criterion are adopted to determine the fiber/matrix interface debonded length and matrix multi-fracture density. The temperature-dependent fiber/matrix interface shear stress, Young's modulus of the matrix, the matrix fracture energy, and the fiber/matrix interface debonded energy are considered in the micro-stress field analysis, fiber/matrix interface debonding criterion, and matrix multi-fracture model. The effects of fiber volume fraction, fiber/matrix interface shear stress, fiber/matrix interface frictional coefficient, fiber/matrix interface debonded energy, matrix fracture energy, and temperature on the matrix multi-fracture of SiC/SiC composite are discussed. When the fiber volume fraction and matrix fracture energy increase, the first matrix cracking stress and matrix saturation cracking stress increase; when the fiber/matrix interface shear stress and interface frictional coefficient increase, the first matrix cracking stress, saturation matrix cracking stress, and saturation matrix cracking density increase with the decrease of the fiber/matrix interface debonded length; when the fiber/matrix interface debonded energy increases, the saturation matrix cracking stress decreases and the saturation matrix cracking density increases due to the decrease of fiber/matrix interface debonding ratio. The experimental matrix multi-fracture and fiber/matrix interface debonding curves of unidirectional SiC/SiC composite at elevated temperatures are predicted. The predicted results agree with experimental data, which proves the efficiency of the developed matrix multi-fracture model. [ABSTRACT FROM AUTHOR]

The deformation of 2D and 2.5 C/SiC woven ceramic-matrix composites (CMCs) in monotonic and cyclic loadings has been investigated. Statistical matrix multicracking and fiber failure models and the fracture mechanics interface debonding approach are used to determine the spacing of matrix cracks, the debonded length of interface, and the fraction of broken fibers. The effects of fiber volume fraction and fiber Weibull modulus on the damage evolution in the composites and on their tensile stress-strain curves are analyzed. When matrix multicracking and fiber/matrix interface debonding occur, the fiber slippage relative to the matrix in the debonded interface region of the 0° warp yarns is the main reason for the emergance of stress-strain hysteresis loops for 2D and 2.5D woven CMCs. A model of these loops is developed, and histeresis loops for the composites in cyclic loadings/unloadings are predicted. [ABSTRACT FROM AUTHOR]

Based on continuum damage mechanics (CDM), a sophisticated 3D mesoscale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding. [ABSTRACT FROM AUTHOR]

In this paper, the strength degradation of non-oxide and oxide/oxide fiber-reinforced ceramic-matrix composites (CMCs) subjected to cyclic loading at elevated temperatures in oxidative environments has been investigated. Considering damage mechanisms of matrix cracking, interface debonding, interface wear, interface oxidation and fibers fracture, the composite residual strength model has been established by combining the micro stress field of the damaged composites, the damage models, and the fracture criterion. The relationships between the composite residual strength, fatigue peak stress, interface debonding, fibers failure and cycle number have been established. The effects of peak stress level, initial and steady-state interface shear stress, fiber Weibull modulus and fiber strength, and testing temperature on the degradation of composite strength and fibers failure have been investigated. The evolution of residual strength versus cycle number curves of non-oxide and oxide/oxide CMCs under cyclic loading at elevated temperatures in oxidative environments have been predicted. [ABSTRACT FROM AUTHOR]

In this paper, the synergistic effects of temperatrue and oxidation on matrix cracking in fiber-reinforced ceramic-matrix composites (CMCs) has been investigated using energy balance approach. The shear-lag model cooperated with damage models, i.e., the interface oxidation model, interface debonding model, fiber strength degradation model and fiber failure model, has been adopted to analyze microstress field in the composite. The relationships between matrix cracking stress, interface debonding and slipping, fiber fracture, oxidation temperatures and time have been established. The effects of fiber volume fraction, interface properties, fiber strength and oxidation temperatures on the evolution of matrix cracking stress versus oxidation time have been analyzed. The matrix cracking stresses of C/SiC composite with strong and weak interface bonding after unstressed oxidation at an elevated temperature of 700 °C in air condition have been predicted for different oxidation time. [ABSTRACT FROM AUTHOR]

In this paper, the effect of multiple matrix cracking modes on cyclic loading/unloading hysteresis loops of 2D woven ceramic-matrix composites (CMCs) has been investigated. The interface slip between fibers and the matrix existed in matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, are considered as the major reason for hysteresis loops of 2D woven CMCs. The effects of fiber volume content, peak stress, matrix crack spacing, interface properties, matrix cracking mode proportion and interface wear on interface slip and hysteresis loops have been analyzed. The cyclic loading/unloading hysteresis loops of 2D woven SiC/SiC composite corresponding to different peak stresses have been predicted using the present analysis. It was found that the damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire cracking modes of the composite, increases with increasing peak stress. [ABSTRACT FROM AUTHOR]

An analytical method has been developed to investigate the effect of interface wear on the tensile strength of carbon fiber − reinforced ceramic − matrix composites (CMCs) under multiple fatigue loading. The Budiansky − Hutchinson − Evans shear − lag model was used to describe the micro stress field of the damaged composite considering fibers failure and the difference existed in the new and original interface debonded region. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress degradation model and fibers strength degradation model have been adopted to analyze the interface wear effect on the tensile strength of the composite subjected to multiple fatigue loading. Under tensile loading, the fibers failure probabilities were determined by combining the interface wear model and fibers failure model based on the assumption that the fiber strength is subjected to two − parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the Global Load Sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength corresponding to multiple fatigue peak stress levels and different cycle number have been analyzed. [ABSTRACT FROM AUTHOR]

To better understand the periodically distributed fractures in rock sequences, the effects of the layer interfaces on the evolution of the stress distribution in a fracture-bound block and on the fracture infilling process are discussed. A three-layer model is developed based on a cohesive zone model (CZM) for layer interfaces and a plastic-damaged model for rock layers. The results indicate that the interface shear strength can greatly influence the stress distribution in a fracture-bound block so that the ratio of the fracture spacing to the layer thickness ( S/ T) is not the dominant factor in the stress state. If interface debonding occurs, the tensile stress in a fracture-bound block can decrease to zero even for a higher S/ T ratio. If the interface shear strength is high enough, a new fracture can further infill between two adjacent preexisting fractures even if the S/ T ratio is at a low level. The fracture process implies that there is a critical value for the interfacial shear strength that controls the fracture pattern between the central layer and its neighboring layers to be either interface debonding or layer-parallel fracture. Both interfacial debonding and layer-parallel fracture can separate the central layer from its neighboring layers and thus lead to fracture saturation. Further analysis indicates that the critical shear strength increases linearly with increasing tensile strength of the central layer. [ABSTRACT FROM AUTHOR]

Intra-ply or inter-ply slippages are commonly seen at the crack tip impinging upon an interface in laminated anisotropic bodies. An interface slippage could occur in the form of yielding (e.g., a well-bonded ductile layer with plastic yielding) or debonding (e.g., a weak, sliding-free one) along the interface direction. This paper presents a fundamental solution for a crack in one individual brittle part impinging normally upon the interface slippage with the neighboring brittle part of laminated anisotropic materials under tensile loading. A superposition method is employed to explicitly solve the problem which combines the solution of a crack in a perfectly bonded elastic homogeneous medium, the solution of a continuous distribution of dislocations which represent slippage at the interface and an appendix solution which offsets the stress on the crack faces induced by the dislocations. This procedure reduces the problem to a singular integral equation which can be numerically solved by using Chebyshev polynomials. The validity of the present solutions is numerically verified where the traction-free condition on the crack faces and the equilibrium of shear stress along the interface slippage can be really satisfied. Numerical implementations are performed to analyze the influence of interface slippage on cracking and stress redistribution in laminated anisotropic bodies. It is found that interface yielding or interface debonding redistributes the stress ahead of the crack tip in the neighboring uncracked part. The presence of interface yielding or debonding lowers the high stress concentration in the tensile stresses ahead of the crack tip. It is also concluded that interface debonding appears to be more effective in lowering the stress concentration than interface plastic yielding. [ABSTRACT FROM AUTHOR]

This paper presents an experimental analysis on the fatigue behavior in C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply and 2.5D woven, at room and elevated temperatures in air atmosphere. The experimental fatigue life S − N curves of C/SiC composites corresponding to different stress levels and test conditions have been obtained. The damage evolution processes under fatigue loading have been analyzed using fatigue hysteresis modulus and fatigue hysteresis loss energy. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different peak stress, fiber preforms and test conditions have been estimated. It was found that the degradation of interface shear stress and fibres strength caused by oxidation markedly decreases the fatigue life of C/SiC composites at elevated temperature. [ABSTRACT FROM AUTHOR]

An analytical method has been developed to investigate the effect of oxidation on the tensile strength of carbon fiber − reinforced ceramic − matrix composites (CMCs). The Budiansky − Hutchinson − Evans shear − lag model was used to describe the micro stress field of the damaged composite considering fibers failure. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The fiber strength degradation model and oxidation region propagation model have been adopted to analyze the oxidation effect on tensile strength of the composite, which is controlled by diffusion of oxygen gas through matrix cracks. Under tensile loading, the fibers failure probabilities were determined by combining oxidation model and fiber statistical failure model based on the assumption that fiber strength is subjected to two-parameter Weibull distribution and the loads carried by broken and intact fibers statisfy the global load sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength considering oxidation time and temperature have been analyzed. [ABSTRACT FROM AUTHOR]

The stress-strain curves of fiber − reinforced ceramic − matrix composites (CMCs) exhibit obvious non-linear behaviour under tensile loading. The occurrence of multiple damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding and fibers fracture, is the mainly reason for the non-linear characteristic. The micromechanics approach has been developed to predict the tensile stress-strain curves of unidirectional, cross-ply and woven CMCs. The shear-lag model was used to describe the micro stress field of the damaged composite. The damage models were used to determine the evolution of micro damage parameters, i.e., matrix crack spacing, interface debonded length and broken fibers fraction. By combining the shear-lag model with damage models and considering the effect of transverse multicracking in the 90° plies or transverse yarns in cross-ply or woven CMCs, the tensile stress-strain curves of unidirectional, cross-ply, 2D and 2.5D woven CMCs have been predicted. The results agreed with experimental data. [ABSTRACT FROM AUTHOR]

An analytical methodology has been developed to investigate the effect of fiber Poisson contraction on matrix multicracking evolution of fiber-reinforced ceramic-matrix composites (CMCs). The modified shear-lag model incorporated with the Coulomb friction law is adopted to solve the stress distribution in the interface slip region and intact region of the damaged composite. The critical matrix strain energy criterion which presupposes the existence of an ultimate or critical strain energy limit beyond which the matrix fails has been adopted to describe matrix multicracking of CMCs. As more energy is placed into the composite, matrix fractures and the interface debonding occurs to dissipate the extra energy. The interface debonded length under the process of matrix multicracking is obtained by treating the interface debonding as a particular crack propagation problem along the fiber/matrix interface. The effects of the interfacial frictional coefficient, fiber Poisson ratio, fiber volume fraction, interface debonded energy and cycle number on the interface debonding and matrix multicracking evolution have been analyzed. The theoretical results are compared with experimental data of unidirectional SiC/CAS, SiC/CAS-II and SiC/Borosilicate composites. [ABSTRACT FROM AUTHOR]

An analytical method has been developed to investigate the effect of interface wear on fatigue hysteresis behavior in carbon fiber-reinforced ceramic-matrix composites (CMCs). The damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding and interface wear, fibers fracture, slip and pull-out, have been considered. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. Upon first loading to fatigue peak stress and subsequent cyclic loading, the fibers failure probabilities and fracture locations were determined by combining the interface wear model and fiber statistical failure model based on the assumption that the loads carried by broken and intact fibers satisfy the global load sharing criterion. The effects of matrix properties, i.e., matrix cracking characteristic strength and matrix Weibull modulus, interface properties, i.e., interface shear stress and interface debonded energy, fiber properties, i.e., fiber Weibull modulus and fiber characteristic strength, and cycle number on fibers failure, hysteresis loops and interface slip, have been investigated. The hysteresis loops under fatigue loading from the present analytical method were in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

This paper follows on from the earlier study (Part I) which investigated the fatigue behavior of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures. In this paper, a micromechanics approach to predict the fatigue life S−N curves of fiber-reinforced CMCs has been developed considering the fatigue damage mechanism of interface wear or interface oxidation. Upon first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. The two-parameter Weibull model is used to describe fibers strength distribution. The stress carried by broken and intact fibres on the matrix crack plane under fatigue loading is determined based on the Global Load Sharing (GLS) criterion. The fibres failure probabilities under fatigue loading considering the degradation of interface shear stress and fibres strength have been obtained. When the broken fibres fraction approaches critical value, the composite would fatigue fail. The fatigue life S−N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures have been predicted. The predicted results agreed with experimental data. [ABSTRACT FROM AUTHOR]

A coupled cohesive zone model based on an analogy between fracture and contact mechanics is proposed to investigate debonding phenomena at imperfect interfaces due to thermomechanical loading and thermal fields in bodies with cohesive cracks. Traction-displacement and heat flux-temperature relations are theoretically derived and numerically implemented in the finite element method. In the proposed formulation, the interface conductivity is a function of the normal gap, generalizing the Kapitza constant resistance model to partial decohesion effects. The case of a centered interface in a bimaterial component subjected to thermal loads is used as a test problem. The analysis focuses on the time evolution of the displacement and temperature fields during the transient regime before debonding, an issue not yet investigated in the literature. The solution of the nonlinear numerical problem is gained via an implicit scheme both in space and in time. The proposed model is finally applied to a case study in photovoltaics where the evolution of the thermoelastic fields inside a defective solar cell is predicted. [ABSTRACT FROM AUTHOR]

Modeling and prediction of the damage evolution in particle reinforced composites is a complex problem. Microstructure characters such as the particle morphologies, sizes, and distribution significantly affect the damage evolution in composites. A numerical simulation has been performed to investigate the damage evolution of SiC/AA2009 composites. Tensile deformation in SiC/AA2009 composites was simulated using the microstructure-based model constructed from the metallograph. Matrix damage, particle cracking, and interface debonding were simulated combining the ductile damage model, the normal stress criterion, and the maximum stress ratio criterion. The simulation results show that under tensile loading, damage initiates at the interface, and then propagates along the weakest direction. The simulation microstructures agree well with experimental results in which interface debonding, particle cracking, and matrix damage co-exist. In addition, the effects of component properties on the damage evolution are examined for various situations. [ABSTRACT FROM AUTHOR]

The uniaxial tensile behavior of unidirectional C/SiC ceramic-matrix composites at room temperature has been investigated. An approach to predicting the uniaxial tensile stress-strain curve of the unidirectional ceramicmatrix composites is developed. The Budiansky-Hutchinson-Evans shear lag model is used to describe the microstress field of damaged composites. A statistical matrix cracking model, a fracture mechanics interface debonding criterion, and a statistical fiber failure model are used to determine the spacing of matrix cracks, the debonded length of interface, and the volume fraction of failed fibers. By combining the shear lag model and the three damage models, the stress-strain curve at each damage stage is constructed and an exact method for predicting the toughness and strength of the composites is established. The tensile stress-strain curves predicted by the present analysis agree well with experimental data. [ABSTRACT FROM AUTHOR]

The tensile-tensile fatigue behavior of unidirectional C/SiC ceramic matrix composites at room and elevated temperature has been investigated. An approach to estimate the interface shear stress of ceramic matrix composites under fatigue loading has been developed. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region upon unloading and subsequent reloading, the unloading interface reverse slip length and reloading interface new slip length are determined by the fracture mechanics approach. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulatd in terms of interface shear stress. By comparing the experimental hysteresis loss energy with the computational values, the interface shear stress of unidirectional C/SiC ceramic composites corresponding to different cycles at room and elevated temperatures has been predicted. [ABSTRACT FROM AUTHOR]

The loading/unloading tensile behavior of unidirectional C/SiC ceramic matrix composites at room temperature has been investigated. The loading/unloading stress-strain curve exhibits obvious hysteresis behavior. An approach to model the hysteresis loops of ceramic matrix composites including the effect of fiber failure during tensile loading has been developed. By adopting a shear-lag model which includes the matrix shear deformation in the bonded region and friction in the debonded region, the matrix cracking space and interface debonded length are obtained by matrix statistical cracking model and fracture mechanics interface debonded criterion. The two-parameter Weibull model is used to describe the fiber strength distribution. The stress carried by the intact and fracture fibers on the matrix crack plane during unloading and subsequent reloading is determined by the Global Load Sharing criterion. Based on the damage mechanisms of fiber sliding relative to matrix during unloading and subsequent reloading, the unloading interface reverse slip length and reloading interface new slip length are obtained by the fracture mechanics approach. The hysteresis loops of unidirectional C/SiC ceramic matrix composites corresponding to different stress have been predicted. [ABSTRACT FROM AUTHOR]

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The analysis of the dynamic stress on the particle-matrix interface in particle-reinforced composite for the reason that this stress may lead to the microvoids' nucleation due to the interfacial debonding were studied. For simplification, a sphere containing a concentric rigid spherical particle was taken as the representative volume element ( RVE). The Laplace transformation was used to derive the basic equations, and the analytical solutions were obtained by means of Hankel transformation. Moreover, the influences of the inertia and viscosity on the debonding damage were also discussed. [ABSTRACT FROM AUTHOR]

A three-dimensional analytical model based on the principle of minimum potential energy is developed and applied to determine the stress state in a discrete fiber/matrix composite cylinder subjected to axial tensile loading in the fiber direction and containing a non-axisymmetric transverse matrix crack and an interface debond. The friction over the debonded interface is incorporated into the analysis. The strain energy release rates associated with the matrix crack and the interface debonding under the combination of the applied load and the interface frictional force are computed. The strain energy release rate criterion has been employed to evaluate the critical applied loads for the two fracture modes and to assess the competition between propagation of a matrix crack and growth of interface debonding. A parametric study has been carried out. The computed results show that the interface friction plays an important role in the failure of brittle matrix composites. [ABSTRACT FROM AUTHOR]

A solution to the thin plate bending problem of partially bonded dissimilar strips with two bond lines is presented. The two strips are symmetrically bonded with respect to the interface which is on the X-axis. The complex stress functions approach together with the rational mapping function technique are used in the analysis. A concentrated bending moment applied at each strip is considered. Distributions of bending and torsional moments, as well as the stress intensity of debonding (SID) at the debonding tips are obtained, and the debonding extension is investigated. [ABSTRACT FROM AUTHOR]