The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
William A. Curtin - One of the best experts on this subject based on the ideXlab platform.
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Micromechanical design of hierarchical composites using Global Load Sharing theory
Journal of the Mechanics and Physics of Solids, 2016Co-Authors: Varun P. Rajan, William A. CurtinAbstract:Abstract Hierarchical composites, embodied by natural materials ranging from bone to bamboo, may offer combinations of material properties inaccessible to conventional composites. Using Global Load Sharing (GLS) theory, a well-established micromechanics model for composites, we develop accurate numerical and analytical predictions for the strength and toughness of hierarchical composites with arbitrary fiber geometries, fiber strengths, interface properties, and number of hierarchical levels, N. The model demonstrates that two key material properties at each hierarchical level—a characteristic strength and a characteristic fiber length—control the scalings of composite properties. One crucial finding is that short- and long-fiber composites behave radically differently. Long-fiber composites are significantly stronger than short-fiber composites, by a factor of 2N or more; they are also significantly tougher because their fiber breaks are bridged by smaller-scale fibers that dissipate additional energy. Indeed, an “infinite” fiber length appears to be optimal in hierarchical composites. However, at the highest level of the composite, long fibers localize on planes of pre-existing damage, and thus short fibers must be employed instead to achieve notch sensitivity and damage tolerance. We conclude by providing simple guidelines for microstructural design of hierarchical composites, including the selection of N, the fiber lengths, the ratio of length scales at successive hierarchical levels, the fiber volume fractions, and the desired properties of the smallest-scale reinforcement. Our model enables superior hierarchical composites to be designed in a rational way, without resorting either to numerical simulation or trial-and-error-based experimentation.
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Rational design of fiber-reinforced hybrid composites: A Global Load Sharing analysis
Composites Science and Technology, 2015Co-Authors: Varun P. Rajan, William A. CurtinAbstract:An analytical model based on Global Load Sharing (GLS) theory is developed to guide design of fiber-reinforced hybrid composites with superior mechanical properties to single-fiber-type composites. The hybrid is assumed to comprise two types of fibers-low- and high-elongation-with sufficiently different failure strains. Hybridization is found to be most beneficial when small-to-moderate volume fractions of the low-elongation, high-strength/stiffness fibers are added to the high-elongation composite. In this regime, all key properties of the hybrid composite can be maintained or improved, relative to the pure high-elongation composite. Potential gains in stiffness are large (approximate to 50%), and gains in pullout stress are moderate (approximate to 10-30%), while failure strain is maintained by design. Furthermore, using discontinuous low-elongation fibers improves hybrid composite performance because such fibers fragment more gracefully over a wide range of strain. Because composite processing might be easier when both fiber types are discontinuous, the performance of hybrids using discontinuous high-elongation fibers are also investigated, and good performance can be largely maintained if the high-elongation fibers are sufficiently long. The analytical model is supported by exact GLS results, and is thus a useful design tool for developing higher-performance composites by hybridization. (C) 2015 Elsevier Ltd. All rights reserved.
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Quantitative damage detection in CFRP composites: coupled mechanical and electrical models
Composites Science and Technology, 2003Co-Authors: Zhenhai Xia, William A. Curtin, Jae Beom Park, Tomonaga Okabe, Nobuo TakedaAbstract:Electrical resistance in carbon-fiber reinforced polymers has been shown experimentally to be a sensitive measure of internal damage. To quantify the dependence of electrical resistance on mechanical fiber damage at the micromechanical level, a numerical electrical resistor network model has been developed. The electrical model is coupled to the fiber damage through a numerical mechanical model, which here is a shear-lag model; the latter informs the electrical model of the locations of broken fibers and the stresses on unbroken sections of fiber. The electrical model accounts for both the longitudinal fiber electrical conductivity and the occasional fiber-fiber contacts that permit electrical coupling of touching fibers. An earlier analytic model based on the Global Load Sharing (GLS) theory is tested against the numerical simulations. Good agreement is found for voltage leads that contact the ends of all fibers in the composite and when the "electrical ineffective length" in the GLS model is related to the density of fiber contacts f(c) in the numerical model by the relationship delta(ce)(eff) = L/(1 +f(c)L) where L is the sample gauge length. Voltage leads that contact only surface fibers lead to a resistance behavior that cannot be predicted by the analytic model; this demonstrates the spatial sensitivity of the electrical response to damage and the need for simulation models to correlate local electrical response to local damage. Sensitivity of the electrical response to the voltage lead geometry suggests that the coupled numerical model can be used to design electrode arrays to optimize spatial damage detection inside composite structures. (C) 2003 Elsevier Science Ltd. All rights reserved.
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Electromechanical modeling of unidirectional CFRP composites under tensile Loading condition
Composites Part A: Applied Science and Manufacturing, 2002Co-Authors: Jae Beom Park, Tomonaga Okabe, Nobuo Takeda, William A. CurtinAbstract:The present paper addresses the correlation between mechanical damage and the change in electrical resistance of CFRP under tensile Loading. A linear relation between the strain and the electrical resistance of single carbon fibers was obtained experimentally, and the electrical behavior of CFRP under tensile Loading was investigated. At stresses approaching the failure stress, the composite resistance rises non-linearly, which is attributed to damage in the form of broken fibers. These experiments lead to the concept of electrical ineffective length over which a broken fiber does not carry electric current, in analogy to the well-established mechanical ineffective length over which a broken fiber carries reduced stress. Based on this concept, a DC circuit model consisting of a serial array of discrete parallel cells of length equal to the electrical ineffective length is proposed to explain the resistance evolution in the composite. An analytical model for fiber damage evolution within the electrical ineffective length is constructed using the Global Load Sharing model and the Weibull fiber strength distribution, The model successfully explains the experimental results on the resistance change of CFRP under tensile Loading with an electrical ineffective length of 5 mm. (C) 2001 Elsevier Science Ltd. All rights reserved.
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Tensile Strength of Fiber-Reinforced Composites: III. Beyond the Traditional Weibull Model for Fiber Strengths
Journal of Composite Materials, 2000Co-Authors: William A. CurtinAbstract:Commercially available graphite and ceramic fibers exhibit statistical strength distributions having separate Weibull moduli rho' for the scaling of strength versus fiber length and rho for the distribution of strengths across a collection of fibers at fixed length. It is shown that very similar distributions arise if each fiber in a collection of fibers exhibits Weibull length scaling according to rho' but with the scale strength appropriate to each fiber distributed according to a Weibull modulus m, with the relationship rho approximate to m rho'/ root m(2) + rho'(2). An analytic model based on the Global Load Sharing approximation is used to predict the trends in composite tensile strength for composites composed of such fibers. From this insight, an analytic model for the strength of composites containing such fibers, but with Local Load Sharing (LLS), is developed by adapting a previous model. Numerical simulations of the tensile strength under LLS are then presented and excellent agreement in the composite strength distribution between the numerical and analytic models is demonstrated. The new analytic model is applied to predict the tensile strength of several unidirectional graphite/epoxy composites, and the predictions shown agree well with experimental strengths. The differences between theory and experiment approach the order of the uncertainties in underlying fiber strengths and fiber volume fractions in the composites.
Hiroyuki Hamada - One of the best experts on this subject based on the ideXlab platform.
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a comparative study of the mechanical properties and failure behavior of carbon fiber epoxy and carbon fiber polyamide 6 unidirectional composites
Composite Structures, 2017Co-Authors: Masahito Ueda, Yuqiu Yang, Toshi Sugahara, Tomohiro Yokozeki, Hiroyuki HamadaAbstract:Abstract Two types of unidirectional carbon fiber reinforced plastic were fabricated using identical carbon fibers but different matrix systems. Thermoplastic polyamide 6 and thermosetting epoxy were used as matrices. A large number of on-axis tensile tests of unidirectional carbon fiber reinforced polyamide 6 (CF/PA6) and the unidirectional carbon fiber reinforced epoxy (CF/Epoxy) laminates were performed. Mechanical properties and failure behaviors are discussed based on fiber distribution, impregnation conditions and interfacial shear strength. Tensile strengths were predicted by means of a modified Global Load Sharing model and compared with experimental results. Step-by-step tensile tests revealed the fracture process of 0-degree unidirectional CF/PA6 laminates.
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A comparative study of the mechanical properties and failure behavior of carbon fiber/epoxy and carbon fiber/polyamide 6 unidirectional composites
Composite Structures, 2017Co-Authors: Masahito Ueda, Yuqiu Yang, Toshi Sugahara, Tomohiro Yokozeki, Hiroyuki HamadaAbstract:Abstract Two types of unidirectional carbon fiber reinforced plastic were fabricated using identical carbon fibers but different matrix systems. Thermoplastic polyamide 6 and thermosetting epoxy were used as matrices. A large number of on-axis tensile tests of unidirectional carbon fiber reinforced polyamide 6 (CF/PA6) and the unidirectional carbon fiber reinforced epoxy (CF/Epoxy) laminates were performed. Mechanical properties and failure behaviors are discussed based on fiber distribution, impregnation conditions and interfacial shear strength. Tensile strengths were predicted by means of a modified Global Load Sharing model and compared with experimental results. Step-by-step tensile tests revealed the fracture process of 0-degree unidirectional CF/PA6 laminates.
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a study on the failure behavior and mechanical properties of unidirectional fiber reinforced thermosetting and thermoplastic composites
Composites Part B-engineering, 2016Co-Authors: Yuqiu Yang, Toshi Sugahara, Hiroyuki HamadaAbstract:Abstract Failure behavior and mechanical properties of unidirectional (UD) carbon fiber reinforced polyamide 6 (CF/PA6) and epoxy resin (CF/Epoxy) laminates were investigated through tensile tests in this study. The fracture modes of both CF/PA6 and CF/Epoxy were discussed based on the fiber orientation, interfacial properties, Mode II interlaminar fracture toughness and the brush width. Meanwhile, Global Load Sharing (GLS) model was employed to compare with the experimental mechanical properties and corresponding fracture mechanics model was employed to analyze the fracture behavior. The results showed that UD CF/PA6 laminates with weak interface but high Mode II interlaminalr fracture toughness mainly exhibited step-like fracture modes (77%) in interfacial fracture mode (Adhesive failure), while CF/Epoxy laminates with stronger interface but lower Mode II interlaminalr fracture toughness mostly showed splitting fracture mode (69%) in matrix fracture mode (Cohesive failure).
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A study on the failure behavior and mechanical properties of unidirectional fiber reinforced thermosetting and thermoplastic composites
Composites Part B: Engineering, 2016Co-Authors: Yuqiu Yang, Toshi Sugahara, Hiroyuki HamadaAbstract:Abstract Failure behavior and mechanical properties of unidirectional (UD) carbon fiber reinforced polyamide 6 (CF/PA6) and epoxy resin (CF/Epoxy) laminates were investigated through tensile tests in this study. The fracture modes of both CF/PA6 and CF/Epoxy were discussed based on the fiber orientation, interfacial properties, Mode II interlaminar fracture toughness and the brush width. Meanwhile, Global Load Sharing (GLS) model was employed to compare with the experimental mechanical properties and corresponding fracture mechanics model was employed to analyze the fracture behavior. The results showed that UD CF/PA6 laminates with weak interface but high Mode II interlaminalr fracture toughness mainly exhibited step-like fracture modes (77%) in interfacial fracture mode (Adhesive failure), while CF/Epoxy laminates with stronger interface but lower Mode II interlaminalr fracture toughness mostly showed splitting fracture mode (69%) in matrix fracture mode (Cohesive failure).
Hans J. Herrmann - One of the best experts on this subject based on the ideXlab platform.
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Critical ruptures in a bundle of slowly relaxing fibers
Physical Review E, 2008Co-Authors: K. Kovács, Raul Cruz Hidalgo, Hans J. Herrmann, Ferenc Kun, Sándor Nagy, Ignacio PagonabarragaAbstract:We study the damage enhanced creep rupture of disordered materials by means of a fiber bundle model. Broken fibers undergo a slow stress relaxation modeled by a Maxwell element whose stress exponent m can vary in a broad range. Under Global Load Sharing we show that due to the strength disorder of fibers, the lifetime tf of the bundle has sample-to-sample fluctuations characterized by a log-normal distribution independent of the type of disorder. We determine the Monkman-Grant relation of the model and establish a relation between the rupture life tf and the characteristic time tm of the intermediate creep regime of the bundle where the minimum strain rate is reached, making possible reliable estimates of tf from short term measurements. Approaching macroscopic failure, the deformation rate has a finite time power law singularity whose exponent is a decreasing function of m. On the microlevel the distribution of waiting times is found to have a power law behavior with m-dependent exponents different below and above the critical Load of the bundle. Approaching the critical Load from above, the cutoff value of the distributions has a power law divergence whose exponent coincides with the stress exponent of Maxwell elements.
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Discrete fracture model with anisotropic Load Sharing
Journal of Statistical Mechanics: Theory and Experiment, 2008Co-Authors: Raul Cruz Hidalgo, Stefano Zapperi, Hans J. HerrmannAbstract:A two-dimensional fracture model in which the interaction among elements is modeled by an anisotropic stress-transfer function is presented. The influence of anisotropy on the macroscopic properties of the samples is clarified, by interpolating between several limiting cases of Load Sharing. Furthermore, the critical stress and the distribution of failure avalanches are obtained numerically for different values of the anisotropy parameter α and as a function of the interaction exponent γ. From numerical results, one can certainly conclude that the anisotropy does not change the crossover point γc = 2 in two dimensions. Hence, in the limit of infinite system size, the crossover value γc = 2 between local and Global Load Sharing is the same as the one obtained in the isotropic case. In the case of finite systems, however, for γ≤2, the Global Load Sharing behavior is approached very slowly.
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extension of fibre bundle models for creep rupture and interface failure
International Journal of Fracture, 2006Co-Authors: R C Hidalgo, Frank Raischel, Hans J. HerrmannAbstract:We present two extensions of the classical fibre bundle model to study the creep rupture of heterogeneous materials and the shear failure of glued interfaces of solid blocks. To model creep rupture, we assume that the fibres of a parallel bundle present time dependent behaviour under an external Load and fail when the deformation exceeds their local breaking threshold. Assuming Global Load Sharing among fibres, analytical and numerical calculations showed that there exists a critical Load below which only partial failure occurs while above which the system fails Globally after a finite time. Approaching the critical point from both sides the system exhibits scaling behaviour which implies that creep rupture is analogous to continuous phase transitions. To describe interfacial failure, we model the interface as an array of elastic beams which experience stretching and bending under shear Load and break if the two deformation modes exceed randomly distributed breaking thresholds. The two breaking modes can be independent or combined in the form of a von Mises type breaking criterion. In the framework of Global Load Sharing, we obtain analytically the macroscopic constitutive behaviour of the system and describe the microscopic process of the progressive failure of the interface.
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Failure process of a bundle of plastic fibers.
Physical review. E Statistical nonlinear and soft matter physics, 2006Co-Authors: Frank Raischel, Ferenc Kun, Hans J. HerrmannAbstract:We present an extension of fiber bundle models considering that failed fibers still carry a fraction 0 < or = alpha < or = 1 of their failure Load. The value of alpha interpolates between the perfectly brittle failure (alpha = 0) and perfectly plastic behavior (alpha = 1) of fibers. We show that the finite Load bearing capacity of broken fibers has a substantial effect on the failure process of the bundle. In the case of Global Load Sharing it is found that for alpha --> 1 the macroscopic response of the bundle becomes perfectly plastic with a yield stress equal to the average fiber strength. On the microlevel, the size distribution of avalanches has a crossover from a power law of exponent approximately 2.5 to a faster exponential decay. For localized Load Sharing, computer simulations revealed a sharp transition at a well-defined value alpha(c) from a phase where macroscopic failure occurs due to localization as a consequence of local stress enhancements, to another one where the disordered fiber strength dominates the damage process. Analyzing the microstructure of damage, the transition proved to be analogous to percolation. At the critical point alpha(c), the spanning cluster of damage is found to be compact with a fractal boundary. The distribution of bursts of fiber breakings shows a power-law behavior with a universal exponent approximately 1.5 equal to the mean-field exponent of fiber bundles of critical strength distributions. The model can be relevant to understand the shear failure of glued interfaces where failed regions can still transmit Load by remaining in contact.
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Failure process of a bundle of plastic fibers.
Physical Review E, 2006Co-Authors: Frank Raischel, Ferenc Kun, Hans J. HerrmannAbstract:We present an extension of fiber bundle models considering that failed fibers still carry a fraction $0\ensuremath{\leqslant}\ensuremath{\alpha}\ensuremath{\leqslant}1$ of their failure Load. The value of $\ensuremath{\alpha}$ interpolates between the perfectly brittle failure $(\ensuremath{\alpha}=0)$ and perfectly plastic behavior $(\ensuremath{\alpha}=1)$ of fibers. We show that the finite Load bearing capacity of broken fibers has a substantial effect on the failure process of the bundle. In the case of Global Load Sharing it is found that for $\ensuremath{\alpha}\ensuremath{\rightarrow}1$ the macroscopic response of the bundle becomes perfectly plastic with a yield stress equal to the average fiber strength. On the microlevel, the size distribution of avalanches has a crossover from a power law of exponent $\ensuremath{\approx}2.5$ to a faster exponential decay. For localized Load Sharing, computer simulations revealed a sharp transition at a well-defined value ${\ensuremath{\alpha}}_{c}$ from a phase where macroscopic failure occurs due to localization as a consequence of local stress enhancements, to another one where the disordered fiber strength dominates the damage process. Analyzing the microstructure of damage, the transition proved to be analogous to percolation. At the critical point ${\ensuremath{\alpha}}_{c}$, the spanning cluster of damage is found to be compact with a fractal boundary. The distribution of bursts of fiber breakings shows a power-law behavior with a universal exponent $\ensuremath{\approx}1.5$ equal to the mean-field exponent of fiber bundles of critical strength distributions. The model can be relevant to understand the shear failure of glued interfaces where failed regions can still transmit Load by remaining in contact.
Frank W. Zok - One of the best experts on this subject based on the ideXlab platform.
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Effects of non-uniform strains on tensile fracture of fiber-reinforced ceramic composites
Journal of the Mechanics and Physics of Solids, 2012Co-Authors: Varun P. Rajan, Frank W. ZokAbstract:Effects of non-uniform strains on tensile fracture of fiber-reinforced ceramic–matrix composites have not been satisfactorily explained by existing mechanics-based models. In this paper, we use an exact model of fiber fragmentation under Global Load Sharing conditions to predict fracture in three model problems in which non-uniform strains occur: (i) an end-constrained plate subject to a linear transverse temperature gradient; (ii) an internally-pressurized cylindrical tube with a linear through-thickness temperature gradient; and (iii) a rectangular beam under combined bending and tension. Fracture is assumed to occur when the Global Load reaches a maximum value. Approximations to the exact fragmentation model are also assessed, with the goal of decoupling the effects of two important parts of the computed stress–strain response: the rate of post-peak strain softening and the magnitude of the plateau “flow” stress once fiber fragmentation is complete. We find that for cases in which the fiber Weibull modulus is low and hence its plateau strength is high relative to its peak and the Loading yields a sufficiently high strain gradient, the failure strain lies in the plateau regime. Consequently, the results can be predicted with good accuracy using a perfectly-plastic representation of the post-peak response. In contrast, for cases in which the fiber Weibull modulus is high, the failure strain lies in the softening portion of the curve. Here a linear-softening model is found to yield accurate results. A preliminary assessment of the model has been made by comparing predicted and measured bending/tension strength and failure strain ratios for one specific composite. The correlations appear good, though additional experiments are required in order to critically assess the model predictions over a range of Loading scenarios.
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application of weakest link fracture statistics to fiber reinforced ceramic matrix composites
Journal of the American Ceramic Society, 2005Co-Authors: John C. Mcnulty, Frank W. ZokAbstract:The strength and reliability of fiber-reinforced ceramic-matrix composites (CMCs) are dependent on whether conditions of local or Global Load Sharing prevail. Global Load Sharing is promoted by a low interfacial sliding stress and is manifested in a zero-tangent modulus at the point of tensile failure along with random fiber failures and extensive fiber pullout. In this paper, it is demonstrated that conditions of Global Load Sharing are not present in two commonly studied CMCs, despite the fibrous appearance of their fracture surfaces. This behavior is manifested in a volume-dependent strength, as evidenced by strength differences measured in tension and flexure (accounting for the nonlinear stress distribution in flexure). Methods of weakest-link statistics are used to relate the strengths measured in the two test configurations. Estimates for the Weibull moduli of the two systems are obtained from the experiments and compared with values obtained through Monte Carlo simulations based on a three-dimensional-lattice Greens function method. The implications of these results on the strength of large components and of small regions of high stress concentration are discussed briefly.
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Application of Weakest‐Link Fracture Statistics to Fiber‐Reinforced Ceramic‐Matrix Composites
Journal of the American Ceramic Society, 2005Co-Authors: John C. Mcnulty, Frank W. ZokAbstract:The strength and reliability of fiber-reinforced ceramic-matrix composites (CMCs) are dependent on whether conditions of local or Global Load Sharing prevail. Global Load Sharing is promoted by a low interfacial sliding stress and is manifested in a zero-tangent modulus at the point of tensile failure along with random fiber failures and extensive fiber pullout. In this paper, it is demonstrated that conditions of Global Load Sharing are not present in two commonly studied CMCs, despite the fibrous appearance of their fracture surfaces. This behavior is manifested in a volume-dependent strength, as evidenced by strength differences measured in tension and flexure (accounting for the nonlinear stress distribution in flexure). Methods of weakest-link statistics are used to relate the strengths measured in the two test configurations. Estimates for the Weibull moduli of the two systems are obtained from the experiments and compared with values obtained through Monte Carlo simulations based on a three-dimensional-lattice Greens function method. The implications of these results on the strength of large components and of small regions of high stress concentration are discussed briefly.
Li Longbiao - One of the best experts on this subject based on the ideXlab platform.
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Tensile strength of ceramic-matrix composites
Durability of Ceramic-Matrix Composites, 2020Co-Authors: Li LongbiaoAbstract:Abstract In this chapter, the tensile strength of fiber-reinforced ceramic-matrix composites (CMCs) subjected to cyclic Loading is investigated. The damage mechanisms of matrix cracking, including fiber–matrix interface debonding, fibers fracture, fatigue-related interface wear and oxidation, and fibers oxidation at elevated temperature are considered in the strength model. The Global Load Sharing criterion and Weibull strength distribution model are combined to determine the fibers fracture at the interface debonded and bonded region. The theoretical relationships between the peak stress, cycle number, matrix cracking, fibers, and interface properties on the fibers failure and residual strength are established. The residual strength of different fiber-reinforced CMCs subjected to cyclic fatigue Loading at room and elevated temperatures are predicted.
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Fatigue Life Prediction of 2D Woven Ceramic-Matrix Composites at Room and Elevated Temperatures
Journal of Materials Engineering and Performance, 2017Co-Authors: Li LongbiaoAbstract:In this paper, the fatigue life of 2D woven ceramic-matrix composites, i.e., SiC/SiC, SiC/Si-N-C, SiC/Si-B4C, and Nextel 610™/Aluminosilicate, at room and elevated temperatures has been predicted using the micromechanics approach. An effective coefficient of the fiber volume fraction along the Loading direction (ECFL) was introduced to describe the fiber architecture of preforms. The Budiansky-Hutchinson-Evans shear-lag model was used to describe the microstress 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 interface shear stress and fibers strength degradation model and oxidation region propagation model have been adopted to analyze the fatigue and oxidation effects on fatigue life of the composite, which is controlled by interface frictional slip and diffusion of oxygen gas through matrix multicrackings. Under cyclic fatigue Loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperatures, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the Load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composites fatigue fractures. The fatigue life S-N curves of 2D SiC/SiC, SiC/Si-N-C, SiC/Si-B4C, and Nextel 610™/Aluminosilicate composites at room temperature and 800, 1000 and 1200 °C in air and steam have been predicted.
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Synergistic Effects of Temperature, Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading
Applied Composite Materials, 2016Co-Authors: Li LongbiaoAbstract:In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue Loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the Load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S–N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.
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Fatigue Life Prediction of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures. Part I: Experimental Analysis
Applied Composite Materials, 2015Co-Authors: Li LongbiaoAbstract: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.
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Modeling the Effect of Oxidation on Tensile Strength of Carbon Fiber−Reinforced Ceramic−Matrix Composites
Applied Composite Materials, 2015Co-Authors: Li LongbiaoAbstract: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.