The present study examines various damage progression criteria to provide input to a shear-lag analysis of ceramic matrix composites (CMCs). The shear-lag as well as other analysis methods require matrix and fiber crack densities in addition to interfacial debond lengths as input to the analysis before the composite behavior can be approximated. The present approach examines criteria for damage progression consisting of a critical matrix strain energy to control matrix crack density, a Weibull-type damage progression scheme for fiber cracks, and ultimate interfacial shear stress to provide debond lengths. Fatigue modeling is also accomplished through an effective fiber pullout where the eventual failure in fatigue is modeled by the available elastic energy exceeding the work to fiber pullout.
{"title":"A Systematic Shear-Lag Approach for Analyzing the Failure Mechanisms in Ceramic Matrix Composites","authors":"D. D. Robertson, J. Solti, S. Mall","doi":"10.1115/imece1996-0484","DOIUrl":"https://doi.org/10.1115/imece1996-0484","url":null,"abstract":"\u0000 The present study examines various damage progression criteria to provide input to a shear-lag analysis of ceramic matrix composites (CMCs). The shear-lag as well as other analysis methods require matrix and fiber crack densities in addition to interfacial debond lengths as input to the analysis before the composite behavior can be approximated. The present approach examines criteria for damage progression consisting of a critical matrix strain energy to control matrix crack density, a Weibull-type damage progression scheme for fiber cracks, and ultimate interfacial shear stress to provide debond lengths. Fatigue modeling is also accomplished through an effective fiber pullout where the eventual failure in fatigue is modeled by the available elastic energy exceeding the work to fiber pullout.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115486640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a model capable of evaluation of principal micromechanical processes taking place in brittle matrix composites reinforced by ductile particles. The reinforcing mechanism is based on formation of a system of restrictive forces imposed on the crack surfaces by the plastic particles behind the propagating crack front. The particles form the bridging zone and, thus, constrain the crack opening. This is the principal aspect of the toughening mechanism in these systems. The developed model addresses the effects associated with the discrete particle distribution and particle-matrix interface properties. The developed analytical approach allows us to trace the crack propagation through this system at any intermediate step. This detailed analysis explains certain aspects of the particulate reinforcement mechanism not discussed in the literature previously. The crack growth resistance curves are presented for several composite systems.
{"title":"Failure Development in Particulate Composites","authors":"A. Rubinstein, Peng Wang","doi":"10.1115/imece1996-0494","DOIUrl":"https://doi.org/10.1115/imece1996-0494","url":null,"abstract":"\u0000 We present a model capable of evaluation of principal micromechanical processes taking place in brittle matrix composites reinforced by ductile particles. The reinforcing mechanism is based on formation of a system of restrictive forces imposed on the crack surfaces by the plastic particles behind the propagating crack front. The particles form the bridging zone and, thus, constrain the crack opening. This is the principal aspect of the toughening mechanism in these systems. The developed model addresses the effects associated with the discrete particle distribution and particle-matrix interface properties. The developed analytical approach allows us to trace the crack propagation through this system at any intermediate step. This detailed analysis explains certain aspects of the particulate reinforcement mechanism not discussed in the literature previously. The crack growth resistance curves are presented for several composite systems.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130287675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A modified shear-lag model suitable for describing bridging fiber stress in metal matrix composites subjected to fatigue loadings has been developed. The model considers the influence of the stress field in the fiber/matrix bonded zone as well as the ratio of the reversed to non-reversed sliding length within the interface debonding region of the fiber. Parameters representing the post-processing residual stress field and the load ratio of the applied loading cycle are also considered.
{"title":"Bridging Fiber Stress in Metal Matrix Composites: An Analytical Model","authors":"H. Ghonem","doi":"10.1115/imece1996-0499","DOIUrl":"https://doi.org/10.1115/imece1996-0499","url":null,"abstract":"A modified shear-lag model suitable for describing bridging fiber stress in metal matrix composites subjected to fatigue loadings has been developed. The model considers the influence of the stress field in the fiber/matrix bonded zone as well as the ratio of the reversed to non-reversed sliding length within the interface debonding region of the fiber. Parameters representing the post-processing residual stress field and the load ratio of the applied loading cycle are also considered.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130739890","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In recent years the design and performance of aerospace vehicles changed due to enhancement and improvement in the design and the materials employed. Special consideration has to be given to the performance of the materials chosen for such vehicles. Titanium matrix composites (TMC) have been identified among the metal matrix composites as candidate materials capable of sustaining the arising loads while maintaining their structural integrity. Material behavior during fatigue loading has to be given special consideration since this loading condition is dominant during the flight regime. Material degradation due to fatigue loading is modeled using a micro-mechanical fatigue damage model for uni-directional metal matrix composites. The evolution of damage is considered at the constituent level by employing a damage criteria for each individual constituent. The overall material damage is obtained by using the Mori-Tanaka averaging scheme. A numerical implementation of the model is used to demonstrate its capabilities by presenting the analytical results for damage evolution in the fibers as well as in the matrix material for isothermal high cycle fatigue loading. Results for varying material and model parameters are also presented.
{"title":"Fatigue Damage in Metal Matrix Composites","authors":"G. Voyiadjis, R. Echle","doi":"10.1115/imece1996-0488","DOIUrl":"https://doi.org/10.1115/imece1996-0488","url":null,"abstract":"\u0000 In recent years the design and performance of aerospace vehicles changed due to enhancement and improvement in the design and the materials employed. Special consideration has to be given to the performance of the materials chosen for such vehicles. Titanium matrix composites (TMC) have been identified among the metal matrix composites as candidate materials capable of sustaining the arising loads while maintaining their structural integrity. Material behavior during fatigue loading has to be given special consideration since this loading condition is dominant during the flight regime. Material degradation due to fatigue loading is modeled using a micro-mechanical fatigue damage model for uni-directional metal matrix composites. The evolution of damage is considered at the constituent level by employing a damage criteria for each individual constituent. The overall material damage is obtained by using the Mori-Tanaka averaging scheme. A numerical implementation of the model is used to demonstrate its capabilities by presenting the analytical results for damage evolution in the fibers as well as in the matrix material for isothermal high cycle fatigue loading. Results for varying material and model parameters are also presented.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130617192","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper reports on our efforts to demonstrate the significance of free edge effects on the effective response of a unidirectional composite under combined thermal and transverse loading and to validate the predictions of an analytical model through the careful design and testing of composite specimens. Included in this study are the demonstration of potential failure modes and the predictions for the micromechanical stress fields which define damage initiation and the constituent energy release rates governing crack propagation within the constituents and along the interfaces. The theoretical predictions for damage development and propagation are in good agreement with the experimental measurements and observations and demonstrate the importance of free edge stresses in controlling damage initiation and subsequent response.
{"title":"Micromechanical Edge Effects in Glass Matrix Composites","authors":"G. Tandon, R. Kim, R. Dutton","doi":"10.1115/imece1996-0469","DOIUrl":"https://doi.org/10.1115/imece1996-0469","url":null,"abstract":"\u0000 This paper reports on our efforts to demonstrate the significance of free edge effects on the effective response of a unidirectional composite under combined thermal and transverse loading and to validate the predictions of an analytical model through the careful design and testing of composite specimens. Included in this study are the demonstration of potential failure modes and the predictions for the micromechanical stress fields which define damage initiation and the constituent energy release rates governing crack propagation within the constituents and along the interfaces. The theoretical predictions for damage development and propagation are in good agreement with the experimental measurements and observations and demonstrate the importance of free edge stresses in controlling damage initiation and subsequent response.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"381 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116059393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Separablesingular eigensolutions at points of geometric and/or material discontinuity are determined by the finite element method. The method is applicable to n-material anisotropic elastic behavior as shown by Pageau et al. (1995), and to n-material isotropic power-law hardening behavior, including the case of complex eigenvalues for plane stress, as shown by Zhang and Joseph (1996a,b,c). Separable HRR solutions for the nonlinear problem are limited to cases whereall materials have the same hardening exponent. This paper demonstrates these capabilities with several examples that have relevance to ceramic coatings on metal substrates. The examples include the elastic case of a crack touching an isotropic-orthotropic interface, and several power-law hardening cases for bi-material systems. Both plane strain and plane stress solutions are considered.
几何和/或材料不连续点处的可分奇异特征解由有限元法确定。该方法适用于Pageau et al.(1995)所示的n-材料各向异性弹性行为，也适用于n-材料各向同性幂律硬化行为，包括平面应力的复特征值情况，如Zhang和Joseph (1996a,b,c)所示。非线性问题的可分离HRR解仅限于所有材料具有相同硬化指数的情况。本文用几个与金属基板上的陶瓷涂层相关的例子来证明这些能力。这些例子包括裂纹接触各向同性-正交异性界面的弹性情况，以及双材料系统的幂律硬化情况。同时考虑平面应变和平面应力解。
{"title":"A Finite Element Method for Separable HRR Solutions in Bi-Material Systems","authors":"Ningsheng Zhang, P. Joseph, A. Kaya","doi":"10.1115/imece1996-0464","DOIUrl":"https://doi.org/10.1115/imece1996-0464","url":null,"abstract":"\u0000 Separablesingular eigensolutions at points of geometric and/or material discontinuity are determined by the finite element method. The method is applicable to n-material anisotropic elastic behavior as shown by Pageau et al. (1995), and to n-material isotropic power-law hardening behavior, including the case of complex eigenvalues for plane stress, as shown by Zhang and Joseph (1996a,b,c). Separable HRR solutions for the nonlinear problem are limited to cases whereall materials have the same hardening exponent. This paper demonstrates these capabilities with several examples that have relevance to ceramic coatings on metal substrates. The examples include the elastic case of a crack touching an isotropic-orthotropic interface, and several power-law hardening cases for bi-material systems. Both plane strain and plane stress solutions are considered.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125890288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A combined numerical and experimental analysis of a unidirectional titanium matrix composite (SCS-6/Timetal 21S) under a series of transverse loadings and unloadings is capable of separating the interfacial fiber-matrix bond strength into two distinct components: one associated with chemical bonding and the other with mechanical bonding. The influence of the mechanical bonding, which is the clamping due to the thermal residual stress state, is determined by finite element analysis with an imperfectly-bonded interface. The chemical bond strength is deduced by subtracting the mechanical bond strength component from the experimental response. Combined numerical and experimental analyses were conducted at two temperatures. At 25°C, the initial inelastic deformation from fiber-matrix separation is controlled by the mechanical component of the bond which is much larger than the chemical component; however, at 650°C, it is controlled by the chemical component. The mechanical bond strength is very dependent on temperature, whereas the chemical bond strength is only weakly dependent on temperature. In addition, the transverse response of unidirectional SCS-6/Timetal 21S was numerically determined for a wide range of temperatures (25°C to 815°C) and strain rates (8.33 × 10−4 1/s to 8.33 × 10−6 1/s) for both perfectly- and imperfectly-bonded cases.
{"title":"Characterization of Inelastic Deformation During the Transverse Loading of Weakly-Bonded Unidirectional Metal Matrix Composites","authors":"R. Neu, J. Kroupa","doi":"10.1115/imece1996-0474","DOIUrl":"https://doi.org/10.1115/imece1996-0474","url":null,"abstract":"\u0000 A combined numerical and experimental analysis of a unidirectional titanium matrix composite (SCS-6/Timetal 21S) under a series of transverse loadings and unloadings is capable of separating the interfacial fiber-matrix bond strength into two distinct components: one associated with chemical bonding and the other with mechanical bonding. The influence of the mechanical bonding, which is the clamping due to the thermal residual stress state, is determined by finite element analysis with an imperfectly-bonded interface. The chemical bond strength is deduced by subtracting the mechanical bond strength component from the experimental response. Combined numerical and experimental analyses were conducted at two temperatures. At 25°C, the initial inelastic deformation from fiber-matrix separation is controlled by the mechanical component of the bond which is much larger than the chemical component; however, at 650°C, it is controlled by the chemical component. The mechanical bond strength is very dependent on temperature, whereas the chemical bond strength is only weakly dependent on temperature. In addition, the transverse response of unidirectional SCS-6/Timetal 21S was numerically determined for a wide range of temperatures (25°C to 815°C) and strain rates (8.33 × 10−4 1/s to 8.33 × 10−6 1/s) for both perfectly- and imperfectly-bonded cases.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129526905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ceramic matrix composites (CMCs) provide higher strength and toughness properties than are possible from monolithic ceramics, in addition to the high temperature resistance. The mechanisms of toughness of these materials have been treated extensively, although some confusion exists in characterizing this property, which has been recently addressed in a systematic manner (Sorensen and Talreja 1995). It is, however, of greater importance in most engineering applications that the long term behavior of CMCs remains in a safe regime. In particular, degradation of stiffness and strength under cyclic loading is a major concern.
{"title":"Fatigue of Ceramic Matrix Composites: Damage Mechanisms and Fatigue Life Diagrams","authors":"R. Talreja","doi":"10.1115/imece1996-0481","DOIUrl":"https://doi.org/10.1115/imece1996-0481","url":null,"abstract":"\u0000 Ceramic matrix composites (CMCs) provide higher strength and toughness properties than are possible from monolithic ceramics, in addition to the high temperature resistance. The mechanisms of toughness of these materials have been treated extensively, although some confusion exists in characterizing this property, which has been recently addressed in a systematic manner (Sorensen and Talreja 1995). It is, however, of greater importance in most engineering applications that the long term behavior of CMCs remains in a safe regime. In particular, degradation of stiffness and strength under cyclic loading is a major concern.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"1218 49","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120877146","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A micromechanical model for porous layered materials has been developed. The micromechanical approach for layered materials is combined with a poroelastic constitutive model. Explicit expressions for effective elastic moduli, thermal expansion coefficients, and poroelastic moduli are obtained. The effect of pore pressure on the overall deformation of the composites is described by the effective poroelastic constants. The obtained results reduce to those of layered materials when there are no pores. Applications of the obtained model to thermochemically decomposing composites are discussed.
{"title":"A Micromechanical Model for Layered Porous Materials","authors":"Yinan Wu, N. Katsube","doi":"10.1115/imece1996-0468","DOIUrl":"https://doi.org/10.1115/imece1996-0468","url":null,"abstract":"\u0000 A micromechanical model for porous layered materials has been developed. The micromechanical approach for layered materials is combined with a poroelastic constitutive model. Explicit expressions for effective elastic moduli, thermal expansion coefficients, and poroelastic moduli are obtained. The effect of pore pressure on the overall deformation of the composites is described by the effective poroelastic constants. The obtained results reduce to those of layered materials when there are no pores. Applications of the obtained model to thermochemically decomposing composites are discussed.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124161784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented. The laminate is divided into two or more sublaminates, with each sublaminate modeled with four-noded quadrilateral shell elements. A special, eight-noded hex constraint element connects opposing sublaminate shell elements. It supplies the nodal forces and moments needed to make the two opposing shell elements act as a single shell element until a prescribed failure criterion is satisfied. Once the failure criterion is attained, the connection is broken, creating or growing a discrete delamination. This approach has been implemented in a three-dimensional finite element code. This code uses explicit time integration, and can analyze shell-like structures subjected to large deformations and complex contact conditions. The shell elements can use existing composite material models that include in-plane laminate failure modes. This analysis capability was developed to perform crashworthiness studies of composite structures, and is useful whenever there is a need to estimate peak loads, energy absorption, or the final shape of a highly deformed composite structure. This paper describes the eight-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. Particular attention is focused on the delamination growth criterion, and it is verified that calculated results do not depend on element size. In addition, results for double cantilever beam and end notched flexure specimens are presented and compared to measured data to assess the ability of the present approach to model a growing delamination.
{"title":"Modeling Delamination Growth in Composites","authors":"E. D. Reedy, F. Mello","doi":"10.1115/imece1996-0492","DOIUrl":"https://doi.org/10.1115/imece1996-0492","url":null,"abstract":"\u0000 A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented. The laminate is divided into two or more sublaminates, with each sublaminate modeled with four-noded quadrilateral shell elements. A special, eight-noded hex constraint element connects opposing sublaminate shell elements. It supplies the nodal forces and moments needed to make the two opposing shell elements act as a single shell element until a prescribed failure criterion is satisfied. Once the failure criterion is attained, the connection is broken, creating or growing a discrete delamination. This approach has been implemented in a three-dimensional finite element code. This code uses explicit time integration, and can analyze shell-like structures subjected to large deformations and complex contact conditions. The shell elements can use existing composite material models that include in-plane laminate failure modes. This analysis capability was developed to perform crashworthiness studies of composite structures, and is useful whenever there is a need to estimate peak loads, energy absorption, or the final shape of a highly deformed composite structure.\u0000 This paper describes the eight-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. Particular attention is focused on the delamination growth criterion, and it is verified that calculated results do not depend on element size. In addition, results for double cantilever beam and end notched flexure specimens are presented and compared to measured data to assess the ability of the present approach to model a growing delamination.","PeriodicalId":326220,"journal":{"name":"Aerospace and Materials","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127723193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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