bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of African American and Afro-Caribbean Older Adults' Self-Reported Health Status, Function, and Substance Use
Authors: Keane Florence , Tappen Ruth M. , Williams Christine L. , Rosselli Monica
Published: July 2008

African American and Afro-Caribbean elders differ in regard to ethnic group membership, place of birth, and years of residence in the United States. In this study, the authors compare self-rated health status, function, and reports of substance use in these two groups. Fifty low-income African American and fifty low-income Afro-Caribbean adults older than 55 were matched on gender, income, and age (within a range of 3 years) for this study. Self-reported mental and physical health (SF-8), function (basic and independent activities of daily living), and tobacco and alcohol use were measured. Significant differences between the two ethnic groups were found on four of the SF-8 domains, the physical health summary measure, and tobacco use but not on the mental health summary measure, function, or alcohol use. The differences that emerged suggest a more positive health status and healthier behavior in the immigrant Afro-Caribbean group. Results may be explained by the healthy immigrant effect relating to better health of immigrant as opposed to nonimmigrant populations.
“Nunca Te Toman En Cuenta [They Never Take You Into Account]”
Authors: García-López Gladys
Published: July 2008

The practice of law is an occupation that has historically been dominated by white men. In recent decades, however, a small but growing number of Chicanas have entered this field. Their entry raises a number of questions regarding their occupational incorporation and mobility. This article analyzes the findings from qualitative interviews with 15 Chicana attorneys. These women identify organizational practices embedded in law firms that reinforce racism, sexism, classism, and homophobia. These structural and interactional dynamics often limit opportunities for professional advancement of Chicana attorneys who “cross the border” into this white, male-dominated occupation. This research also illuminates innovative tactics employed by Chicanas to achieve their own definitions of professional “success.” My analysis reveals key mechanisms in workplace structure and interaction that reinforce racially gendered “borders” created by co-workers and supervisors who “nunca toman en cuenta (never take into account)” the presence of successful Chicanas.
Migration as Engendered Practice: Mexican Men, Masculinity, and Northward Migration
Authors: Broughton Chad
Published: July 2008

As Mexico endures the far-reaching economic and social dislocations wrought by neoliberalism, many predominantly rural states in southern Mexico have witnessed an unprecedented northward exodus of working age men and women. This article argues that in response to these intense pressures to emigrate, poor men from rural Mexico do more than make instrumental calculations about migration to the border; they must negotiate masculine ideals and adopt strategic gendered practices in relation to the migration experience and the dynamic economic, social and cultural conditions of the border region. This article finds that men adopt one or a hybrid of three fluid masculine stances—traditionalist, adventurer, and breadwinner—in response to migration pressures in neoliberal Mexico.
On Factors Affecting Localization and Void Growth in Ductile Metals: A Parametric Study
Authors: Horstemeyer M. F. , Ramaswamy S.
Published: July 2008

A large number of factors besides void volume fraction are known to play significant roles in influencing void growth and strain localization. In spite of this, macroscale constitutive models currently available in the literature account for only a few of these factors while describing the evolution for damage, or porosity, in ductile metals. The absence of other contributing factors from the models could be attributed to the fact that past investigations have considered only a few (at most three) while determining their overall influences on void growth and strain localization. The present study seeks to examine the sensitivities exerted by a list of seven independent parameters on strain localization and void growth in Aluminum 1100 and 304 L Stainless Steel by performing a series of parametric calculations using the finite element method. Owing to the wide range of parameters, an optimal matrix of finite element calculations is generated using the statistical method of design of experiments (DOE). The DOE method is also used to screen the finite element results and yield the desired parametric influences as outputs. As far as localization and void growth are concerned, it is observed that, while temperature and microporosity exerted the most dominant influences, pre-strain effects and geometric parameters, such as uniformity as pore size, and the shape and distribution of pores, are noted to play significant secondary influences.
Micromechanically Based Constitutive Models for Damage Evolution in Composite Laminates
Authors: Gudmundson P.
Published: July 2008

The structure of micromechanically based constitutive models for composite laminates developing transverse matrix cracks, local delaminations, fibre/matrix debonding and fibre fractures is discussed. Nondimensional damage variables describing these four damage modes are introduced and the principal form of a damage dependent constitutive law is formulated. As a special case transverse matrix cracking is investigated in further detail. A previously developed model for stiffness changes resulting from transverse matrix cracking is presented, and criteria for initiation and growth of transverse cracks are discussed. In particular, limitations of the linear elastic fracture mechanics approach are investigated and a cohesive zone model capturing crack bridging effects is suggested.
Effect of Load History on Damage Characteristics Near Crack Tips in a Particulate Composite Material
Authors: Liu C. T.
Published: July 2008

The damage field in a precracked particulate composite specimen subjected to a complex cyclic loading history was investigated using acoustic imaging techniques. The acoustic imaging data were analyzed to delineate the damage field ahead of the cracks tips and to generate contour plots of the damage intensity. The results of these analyses were compared and the effect of the loading history on the damage field discussed.
Damage Model for Monotonic and Fatigue Response of High Strength Concrete
Authors: Al-Gadhib A. H. , Baluch M. H. , Shaalan A. , Khan A. R.
Published: July 2008

An anisotropic elasto-damage model for predicting the response of concrete subject to montonic and fatigue loading is presented in this study. The model utilizes a concrete appropriate damage-effect tensor M in constructing the constitutive equations. The concept of multiple bounding surfaces is used, with a varying size limit fracture surface defining fatigue loading in contrast to a fixed size limit fracture surface for monotonic loading. The model after calibration is shown to predict the monotonic, compressive uniaxial stress-strain path for concretes of various strengths as well as S-N curves depicting the fatigue response of concrete.
Application of Isochronous Healing Curves in Predicting Damage Evolution in a Salt Structure
Authors: Chan K. S. , Bodner S. R. , Munson D. E.
Published: July 2008

A treatment of damage healing is present for rock salt, formulated within the framework of continuum damage mechanics. The concept of an isochronous healing surface, which is a locus of points in a stress space for which the times of healing are identical, is proposed and derived from the healing formulation in order to establish the initial stresses for the onset of healing and the evolution of healing with time and stress. The characteristics of the isochronous healing curves are identified and compared against those of isochronous failure curves and the dilatancy boundary. Isochronous healing curves for clean and argillaceous (containing clay particles) salt are developed and evaluated against laboratory data. Subsequently, the isochronous healing curves are used to predict the healing response of damage in the disturbed rock zone of an air intake shaft in a salt structure.
On Low Cycle Fatigue in Metal Matrix Composites
Authors: Pedersen Thomas Ørts , Tvergaard Viggo
Published: July 2008

A numerical cell model analysis is used to study the development of fatigue damage in aluminium reinforced by aligned, short SiC fibres. The material is subjected to cyclic loading with either stress control or strain control, and the matrix material is represented by a cyclic plasticity model, in which continuum damage mechanics is incorporated to model fatigue damage evolution. This material model uses a superposition of kinematic and isotropic hardening, and is able to account for the Bauschinger effect as well as ratchetting, mean stress relaxation, and cyclic hardening or softening. The cell model represents a material with transversely staggered fibres. With focus on low cyclic fatigue, the effect of different fibre aspect ratios, different triaxial stress states, and balanced as well as unbalanced cyclic loading is studied.
Formulation of a Strain Based Orthotropic Elasto-Plastic Damage Theory
Authors: Chan L. C. , Lee T. C. , Fan J. P. , Tang C. Y.
Published: July 2008

A strain based orthotropic elasto-plastic damage theory is derived for solving engineering problems. The basic ideas of the formulation are first explained by the one-dimensional approach. Subsequently, the approach is generalized to develop the theory in three-dimensional space. Damage is characterized by a second order damage tensor D while its effects on mechanical properties are described by a fourth order damage effect tensor M. The concept of elastic energy equivalence is adopted to determine the stress-strain relation in terms of the effective stress and the effective strain. On the basis of the plastic flow rule and the damage potential, the elasto-plastic damage tangent tensor as well as the damage threshold function are obtained. Since the development of damage usually connects with deformation, the strain based theory is easier to use in solving structural problems. An example case of uniaxial stretching of aluminium alloy 2024T3 plate is employed to justify the applicability of the theory. The results show that the theoretical results are in good agreement with the experimental ones.
Damage Modeling in Metal Forming Processes
Authors: Saanouni K. , Nesnas K. , Hammi Y.
Published: July 2008

Fully coupled constitutive equations accounting for isotropic hardening as well as the ductile isotropic damage are implemented into the special purpose finite element code for metal forming simulation. First, the formulation of the fully coupled constitutive equations in the framework of the thermodynamics of irreversible processes with state variables is presented. The associated numerical aspects are then presented and discussed using the implicit integration schemes. The numerical implementation of the damage is made in such a manner that the calculations can be executed with or without damage effect, i.e., coupled or uncoupled calculations. Several numerical results are presented discussing the capability of the model to predict the damage initiation and growth during metal forming processes. For some geometrically simple examples, comparisons between coupled and uncoupled solutions are presented. The proposed methodology is then applied to numerically simulate various metal forming processes in order to predict the damage initiation.
Damage Based Formability Analysis of Sheet Metal with LS-DYNA
Authors: Chow C. L. , Tai W. H.
Published: July 2008

This papers presents a damage mechanics model, which was proposed recently by the authors for predicting the localized necking and final failure of sheet metals. It is generalized to take into account the continuous directional change of principal strain plane and damage plane, and their hysteretic effect on damage evolution. The generalization is a critical requirement to predict accurately the forming limit strains, as most stamped components are subjected to multistage forming process. This type of forming process produces non-proportional stamping force/load and a complex strain history in the stamped part causing directional change of principal strain plane and damage plane. The damage model is implemented into the large-scale finite element package LS-DYNA that then was applied to predict the forming limit strain and fracture limit strain of VDIF under non-proportional loading condition. Satisfactory predictions have been achieved for several case examples where the complex strain histories are prescribed from a practical stamping operation.
A Dislocation-Model of Limit Strain Prediction in Aluminium Sheet Metals under Biaxial Deformation
Authors: Lee W. B. , Wen X. Y
Published: July 2008

The development of strain inhomogeneity and fracture events are influenced to a great extent by the local properties of the microstructures. The effect of dislocation hardening is incorporated into a rate sensitive crystal plasticity model for the prediction of limit strain in biaxial deformation. The assumption of a pre-existing surface groove defect in the Marciniak-Kuczynski method of limit strain prediction is relaxed, and the surface defect is seen to arise from the differential deformation between two colonies of grains with different crystallographic orientations. With the use of a modified localized necking criterion which incorporates the changes in the dislocation density, the limit strain of a sheet metal with two ideal orientations is predicted.
Continuum Damage Mechanics, Anisotropy and Damage Deactivation for Brittle Materials Like Concrete and Ceramic Composites
Authors: Chaboche J. L. , Lesne P. M. , Maire J. F.
Published: July 2008

The main lines of a Continuum Damage Mechanics Modelling are reviewed, for applications to brittle materials treated as elastic damageable ones.

The proposed damage models consider in the same framework the cases of initially isotropic materials like concrete and anisotropic composites.

Attention is focused on the damage deactivation effects and on the possibility to describe irreversible strains directly associated to the damaging processes without any additional dissipation. Finally, the model is applied to two particular SiC/SiC and C/SiC composites.
Waiting Element Structures and Stability under Extension
Authors: Cherkaev Andrej , Slepyan Leonid
Published: July 2008

In this paper the following questions are considered: What are the phenomena which limit the total fracture energy of a structure under the extension before it breaks? When is the limiting energy level more important that the stress limit? What are possible ways to increase the required fracture energy of a sample before it breaks? It is shown that the required features of a material or of a construction can be achieved by using special structures of ordinary elements. The possibilities are discussed for increasing the fracture energy density in a sample, and increasing the total fracture energy in a construction. The dynamic process of damaging discussed as well.
Stochastic Process of Multiple Cracking in Discontinuous Random Fiber Reinforced Brittle Matrix Composites
Authors: Wu Hwai-Chung , Li Vicror C.
Published: July 2008

The classical ACK model for multiple cracking in a tensile specimen of a fiber reinforced brittle matrix composite does not account for flaw size distribution of the matrix. In this paper, a stochastic treatment of the damage process in the form of multiple cracking in discontinuous random fiber reinforced brittle matrix composites is presented. The effect of matrix flaw size distribution (initial matrix damage) on composite strength and crack spacing is analyzed. The flaw size distribution of the matrix is simulated by a Monte Carlo process. In the simulation, a Weibull-type function is assumed. The conditions for crack growth depending on initial flaw size and external loads as well as fiber bridging effect are highlighted. Unique merits and deficiencies of the current study are also discussed.
Effective Spring Constant for Planar Arrays of Circular Cracks
Authors: Huang X. , Karihaloo B. L. , Rose L. R. F.
Published: July 2008

A doubly-periodic array of coplanar circular cracks is used as a micromechanical model for crack bridging due to unbroken ligaments between the crack faces and for a localized deformation band. Two complementary approaches are described for determining the effective spring constant for the unbroken ligaments and the root-mean-square average of the stress intensity factor for the microcracks. The first approach exploits the periodicity to formulate a computationally efficient numerical solution which can be considered to provide exact results for the specific configuration of a doubly-periodic array. The second approach is similar in spirit to the self-consistent procedure for deriving the effective moduli of two-phase composites and leads to explicit analytical approximations. The results obtained for the spring constant by these two approaches are in good agreement over the range of cracked area fraction for which the micromechanical model is most reliable; a consistent difference, but a similar trend, is noted in the results obtained for the stress intensity factor. The relative merits and limitations of the two approaches are briefly discussed.
On Thermomechanics of Martensite Transitions
Authors: Vakulenko A. A.
Published: July 2008

In the last ten to fifteen years, a number of works appeared in which solid-state phase transitions were considered in the framework of mechanics of continua. For example, Grinfeld [2] constructed the equilibrium phase conditions by variational principles formulated in the classical work of Gibbs [1]; note, also, works [3-5] and others. These works, typically, deal with the phase equilibrium conditions only.

This paper addresses, mainly, the diffusionless (martensite) transitions and outlines the thermodynamics of such transitions. The suggested approach allows one to analyze the transition kinetics, and, in particular, the phase equilibrium conditions.
Evolution of Void Shape and Size in Creeping Solids
Authors: Needleman Alan , Tvergaard Viggo , Van Der Giessen Erik
Published: July 2008

A boundary value problem for a periodic array of initially spherical voids in a power law creeping solid is analyzed. An axisymmetric cell model relevant for simulating grain boundary void growth is used. The rate boundary value problem is solved by means of a finite element method. Void growth histories accounting for void shape changes and, within the cell model context, void interaction effects are computed for various remote stress triaxiality states. An automatic remeshing algorithm permits computations for large changes in void size and shape. The computed void growth rates are compared with predictions from available analytical formulas that neglect shape change effects.
Continuum Damage Based on Elastic Projection Operators
Authors: Schreyer H. L.
Published: July 2008

The general formulation for continuum damage, as for plasticity, is so broad that specific conclusions can be made only if simplifying assumptions are made. Experimental data do not support the simplification of isotropic damage. Here, the elasticity tensor is expressed in terms of projection operators and principal elasticities which are altered with damage. A subspace is used to define a damage mode. The result is a theory that predicts a limited amount of anisotropic damage and represents a natural generalization of isotropic damage. The further assumption that a different damage function holds for each mode results in a number of damage surfaces with the lower bound forming the composite damage surface. It is also postulated that a characteristic set of cracks is associated with each mode. Each set is assumed to consist of an isotropic distribution of cracks with a representative crack dimension. However, the set for one mode may be different from the next set so, overall, the crack distribution need not be isotropic nor of one characteristic average dimension. The use of these assumptions results in the uncoupling of damage modes and evolution equations for crack growth and for the principal values of the elasticity tensor. Furthermore, the possible connection between dilatation and the rotation of projection operators is illustrated with a load path based on triaxial compression.
A Theory of Inclusion Debonding and its Influence on the Stress-Strain Relations of a Ductile Matrix Composite
Authors: Zhao Y. H. , Weng G. J.
Published: July 2008

The progressive debonding process and its influence on the overall elastoplastic response of a two-phase, ductile composite containing aligned oblate inclusions are examined as a function of inclusion shape and concentration, and the interfacial strength. The theory developed is based upon a Weibull statistical function to describe the probability of debonding, and Qiu and Weng's (1992) energy approach to determine the internal stress state of the inclusions and the homogenized plastic state of the ductile matrix. The axisymmetric loading condition-in the form of U22 = a33 = (3a -is studied in detail, including the dependence of 0 on the aspect ratio of inclusions and their concentration to produce a purely hydrostatic tensile state in the inclusions. It is shown that the stress-strain curve of the debonding system always starts out with that of a perfectly bonded composite, then deviates from it, and finally approaches that of a porous material containing similarly aligned voids. It is also found that complete debonding is faster with spherical inclusions, and is more difficult with thin circular discs. Debonding is also faster at a lower particle concentration and, as expected, faster when the interfacial strength is weaker. The evolution of volume concentration of the debonded particles (or voids) is also determined for each case to reflect the damage process in the two-phase system.
Continuum Damage Mechanics: When and How?
Authors: Krajcinovic Dusan
Published: July 2008

The present paper reflects on the state of the development of damage mechanics initiated in 1958 by Lazar M. Kachanov who we commemorate with this series of four issues of the International Journal of Damage Mechanics. This paper presents a personal view and an assessment of the accomplishments of a group of dedicated people interested in this new field of solid mechanics. In particular, the paper focuses on the establishment of criteria needed to define the circumstances allowing for the application of a deterministic and local continuum model of traditional type.
Mesh-Dependence in Local Approach to Creep Fracture
Authors: Murakami S. , Liu Y.
Published: July 2008

Mesh-dependence and its regularization in the local approach to creep fracture based on continuum damage mechanics and finite element method are discussed. The essential causes of the mesh-dependence are elucidated first in some detail. Then, the process of damage localization and its effects on the mesh-dependence are discussed by performing finite element analysis of a plate in uniform state of stress. The stress sensitivity in damage evolution equations is shown to be one of the major causes of the mesh-dependence. Finally, besides the non-local damage theory often employed in local approach, three new possibilities, including the stress limitation method and that of the modified stress sensitivity in the damage evolution equation, to secure the convergent results are proposed. The validity and the limitations of these methods are elucidated and compared with each other by analyzing creep fracture process of an axisymmetric thick-walled tube.
On Damage Strain Energy Release Rate Y
Authors: Chen X. F. , Chow C. L.
Published: July 2008

In the application of the theory of damage mechanics to solve a wide range of practical engineering problems, a generalized formulation of damage strain energy release rate Y is required. This is because the damage strain energy release rate Y, which is the thermodynamic conjugate force of damage variable D, is used to derive damage evolution equation. For the case of isotropic damage, the damage variable is degenerated to a scalar. Accordingly, the derivation of the damage strain energy release rate is relatively straightforward. However, it is much more involved in the case of anisotropic damage. Currently, no such generalized form of the damage strain energy release rate is available. This paper is intended to present the development of three formulations of damage strain energy release rate based on three different forms of the damage effect tensor M(D) for which D is a second order symmetric tensor. The realization of the anisotropic damage strain energy rate formulations makes it possible to obtain the solution of practical structural problems where the service loading is often nonproportional.
Elastic and Thermoelastic Properties of Composites Reinforced with Short Axisymmetric Fibers
Authors: Kanaun S. K. , Levin V. M.
Published: July 2008

The article is dedicated to the theoretical investigation of mechanical properties of matrix composites reinforced with short axisymmetric fibers. The advanced self-consistent method (variant of the effective field method) is applied here for evaluation of elastic moduli and coefficients of thermal expansion in solids with short stiff fibers of various types.
Mechanical Response of Semi-Brittle Ceramics Subjected to Tension-Compression State. Part II: Description of Deformation Process
Authors: Sadowski Tomasz
Published: July 2008

Some numerical examples were presented to describe deformation process of semi-brittle polycrystalline ceramic materials, following paper [4]. The damage growth can be modelled as quasi-linear function of the stress state, what is easily applicable to solutions to many practical engineering problems.
Analysis of an Axisymmetric Matrix Crack with Interfacial Debond
Authors: Venkatakrishnaiah S. , Dharani L. R.
Published: July 2008

Interfacial debonding might occur with an increasing tensile load in a unidirectional fiber-reinforced composite. This debonding is assumed to be a significant contributor to increased composite toughness. A model is developed to analyze the stresses and energy release associated with a unidirectional composite containing matrix crack with interfacial debonding. A consistent shear-lag model in cylindrical coordinates is developed and the friction effect at the fiber/matrix interface is modeled by applying constant interfacial stresses in the debonded region. The governing equations are solved using an eigenvalue technique. The debond stresses are compared with the results of the single fiber pull-out experiment. A parametric study is performed for different constant values of interfacial stresses in the debond region, fiber embedded lengths and fiber diameters. A criterion for either the crack penetration or the debond growth is discussed.
Experimental Damage Investigation of a SiC-Ti Aluminide Metal Matrix Composite
Authors: Voyiadjis George Z. , Venson Anthony R.
Published: July 2008

Experimental investigations and procedures for the determination of damage are presented for the macro- and micro-analysis of SiC-Titanium Aluminide metal matrix composite (MMC). Uniaxial tension tests are performed on laminate specimens of two different layups. The layups are balanced symmetrically and given as (0/90)sand (±45)s, each containing four plies. Dogbone shaped flat plate specimens are fabricated from each of the layups. Specimens for the different layups are loaded to various load levels ranging from rupture load down to 70% of the rupture load at room temperature. By loading specimens to various load levels damage evolution is experimentally evaluated through a quantitative micro-analysis technique. Micro-analysis is performed using scanning electron microscopy (SEM) on three mutually perpendicular representative cross sections of all specimens for the qualitative and quantitative determination of damage. Together these representative cross sections form a representative volume element (RVE) defined for the theoretical development of damage evolution. Results from the micro-analysis are used in evaluating the damage parameters defined in a previously developed damage theory [1]. This theory uses a second order damage tensor of which it is proposed will have non-zero off diagonal terms only if the load applied to the laminate is in a direction other than parallel to the fibers. Damage parameters are evaluated for each of the load levels below the rupture load, since damage features present at this load level are beyond the range of valid damage mechanics. Two types of damage evaluations are performed for the RVE, one for the overall quantification of damage and the other quantifying damage in the matrix and fibers separately. Damage as a result of delamination is excluded in this investigation for both types of damage evaluation, but may be included if needed. The damage curves presented show graphically a consistent evolution of damage, which validates the methods used in evaluating the damage parameter. Curves for the different laminate layups show that damage profile curves are similar for different laminate layups and orientations. The off diagonal terms of the damage tensors as evaluated by the proposed scheme are found to be significant and should be included in any constitutive damage relation. Numerical verification of these observations are to be presented in a subsequent paper.
Effective Moduli of Unidirectional Fiber Composites Containing Radial Cracking and Interfacial Debonding
Authors: Liu Sheng , Zhu Jiansen
Published: July 2008

It has been observed that radial cracks may be the initial damage due to processing of advanced composites. It has also been observed that a weak bond or debonding between matrix and fiber is common for metal matrix composites. An inelastic finite element procedure is utilized to perform micromechanics analysis of a Sic/Ti continuous fiber laminated composite for the purpose of analyzing the effect of radial matrix cracks and the fiber-matrix debonding on the homogenized stiffness of a unidirectional fiber composite. Specifically, we are looking at the case where partial debonding and radial crack may co-exist over the entire length of the fiber. The material SiC/Ti is selected for this research. Titanium behaves in elastically after applied loads exceed the material yield point, so that the nonlinear material properties and hardening are considered in modeling. Radial cracks and debondings are modeled by rigorous contact models which may allow arbitrary sliding in order to prevent the crack surfaces from penetration. Both frictionless and frictional contact models are evaluated to model different interface conditions. A unit cell model is chosen and subjected to either uniaxial or shearing loads. The model has been verified by comparing the results with some existing model for simpler cases where no debonding or only open debonding is considered. The results presented show the following: (1) The presence of debondings and cracks may reduce the stiffness of composites. (2) Crack is less important than debonding in terms of the stiffness reduction in the situations we considered here. (3) Debonding is much more important for extension and shearing than for compression. For compression, the stiffness reduction due to the debonding depends on the debonding surface roughness. (4) When compression or shearing loads are applied, a significant portion of debonding surfaces gets into contact, and the friction must be considered. The presence of friction increases the stiffness of the composite. (5) The degree of friction influence on the stiffness depends on the location of the damages and the area of contact.
Modeling of Damage in Composite Materials Submitted to Off Axis Tests: Application to a Ceramic Woven Fabric SiC-SiC Composite
Authors: Aussedat E. , Thionnet A. , Renard J.
Published: July 2008

Woven fabric composites show a damage behavior which can be compared to that of cross-ply laminates concerning transverse cracking. The particularity of woven fabric composites is to have two networks of cracks oriented by the weft and the warp threads. The originality of this paper is to propose a vectorial approach with two damage variables instead of a tensorial one to model the behavior of woven fabric composites. A meso-macro approach is applied. A comparison of numerical simulations and off axis tests leads to an assessment of the accuracy of the proposed modeling methodology.
Equilibrium Paths of Polygonally Damaging Structures Part Two: One-Dimensional Example for Nonsmooth Damage and Localization
Authors: Kurutz Maria
Published: July 2008

In the first part of the paper, stability analysis of nonlinearly inelastic damaging structures is shown by applying polygonal approximation for the nonlinear material functions. The basis of the nonsmooth stability analysis together with a lot of numerical illustrations has originally been laid down in the papers of M. Kurutz (1989, 1993a, 1993b, 1995). In the first part of this paper, the theoretical bases of the nonsmooth damage and localization instabilities of structures having polygonal stress-strain diagrams are presented. In the second part, the numerical illustrations are shown.

The presented example aims to follow the famous historical example of Shanley (1947), related to the elasto-plastic behaviour of the Euler-column. By using a very simple mechanical model of the problem, the damage behaviour of the plastic hinges of the buckled state can be analysed.
Anisotropic Damage for the Characterization of the Onset of Macro-Crack Initiation in Metals
Authors: Voyiadjis George Z. , Park Taehyo
Published: July 2008

The onset of macro-crack initiation in metals is characterized using anisotropic damage. The formulation is for problems where the assumption of small elastic strains is valid (Figure 1). A coupled model of damage and plasticity is used to numerically simulate macro-crack initiation in a center cracked thin plate. The plate is subjected to in-plane uniformly distributed tensile load. A very fine finite element mesh is used to discretize the plate. The stresses and damage are shown in the form of contour lines around the crack tip of the plate.
A Constitutive Theory for Brittle Solids with Application to Concrete
Authors: Yazdani S. , Karnawat S.
Published: July 2008

A single-flow surface model unifying damage mechanics and plasticity is developed for quasi-brittle solids in general and concrete in particular. The necessity of using both plasticity and damage mechanics is discussed, and the preference for developing a single-flow surface model over the existing bi-surface models is outlined. The model is cast within the general setting of the continuum thermodynamics with internal variables. Invoking the internal dissipation inequality and guided by physical arguments, a flow surface is developed via introducing pressure functions. The flow surface displays both hardening and softening. The model is capable of predicting the essential features of material inelasticity including dilatation, anisotropic degradation, inelastic flow, and enhancement in strength and apparent ductility with lateral pressure, and is simple for computer implementation. These features are shown together with comparisons of theoretical and experimental data.
Computational Simulation of Matrix Microslip Bands in SiC/Ti-15 Composite
Authors: Mital S. K. , Lee H. -J. , Murthy P. L. N. , Chamis C. C.
Published: July 2008

Computational simulation procedures are used to identify the key deformation mechanisms for a [0]8 and a [90]8 SiC/Ti-15 metal matrix composite. The computational simulation procedures employed consist of a three-dimensional finite-element analysis and a micromechanics-based computer code METCAN. The interphase properties used in the analysis have been calibrated using the METCAN computer code with the [90]8 experimental stress-strain curve. Results of the simulation show that although shear stresses are sufficiently high to cause the formation of some slip bands in the matrix concentrated mostly near the fibers, the nonlinearity in the composite stress-strain curve in the case of the [9018 composite is dominated by interfacial damage, such as microcracks and debonding rather than microplasticity. The stress-strain curve for the [0]8 composite is largely controlled by the fibers and shows only slight nonlinearity at higher strain levels that could be the result of matrix microplasticity.
Influence of Debonding Damage on a Crack Tip Field in Particulate-Reinforced Ductile-Matrix Composite
Authors: Tohgo Keiichiro , Suzuki Naomori , Ishii Hitoshi
Published: July 2008

This paper deals with damage evolution around a crack tip in particulate-reinforced composite which contains hard particles dispersed homogeneously in a ductile matrix. In such a composite, debonding of particle-matrix interface is significant damage. The damaged particles have a weakening effect on overall mechanical properties of the composite; on the contrary, if the damage process could be controlled, the damage around a crack tip might be available as an energy dissipation mechanism in toughening. A new finite element method is developed based on Tohgo-Chou-Weng's constitutive relation which describes the elastic-plastic behavior and the damage behavior of particulate-reinforced composites. In this constitutive relation, it is assumed that the debonding damage is controlled by the stress of the particle and the statistical behavior of particle-matrix interfacial strength, that the debonded (damaged) particles are regarded as voids, and that a void volume fraction increases with deformation. Analyses of stress/strain field and damage evolution around a crack tip in particulate-reinforced composite are carried out by the FEM. With an increase in stress intensity, the debonding damage spreads out, and the damaged zone is constructed ahead of the crack tip. This debonding damage drastically influences the distributions of macroscopic and microscopic stress/strain fields around the crack tip. The initial particle volume fraction is higher, the damaged region ahead of the crack tip is narrower. This result suggests that the energy dissipation due to the debonding damage cannot be expected in the composite with high content of the particles.
Comparative Study of Stresses Near Crack Tip for Layered and Homogeneous Models of Composite
Authors: Linkov Alexander M. , Mishuris Gennady S.
Published: July 2008

Layered composite, bonded with two half planes, one of which contains a crack, is compared with homogeneous anisotropic media, bonded similar half planes. This problem is analyzed for the case of antiplane strain. Stress singularities are investigated, and numerical results are presented and compared for these models. Conclusions drawn concern thresholds within which the model of homogeneous media can serve to simulate a layered composite.
Damage Evolution in Ductile Materials
Authors: Mou Yanghu , Han Ray P. S.
Published: July 2008

A continuum damage evolution model for ductile materials is derived from the principles of incremental complementary energy and thermodynamics. In accordance with this model, the evolution of damage is dependent on the accumulated strain, the stress triaxiality ratio, and the strain hardening exponent of the material. The predictions of the model are compared with experimental results and it showed that the model is capable of predicting damage evolution with good accuracy. It is also found that of the three factors affecting damage evolution in ductile materials, the stress triaxiality ratio has the greatest influence. The study showed that a faster rate of damage occurs at higher stress triaxiality ratios.
Sensitivity of Material Parameters in the Finite Element Computation of Microvoid Nucleation and Growth
Authors: Lazzarotto L. , Picart P. , Oudin J.
Published: July 2008

A suitable range of microvoided material parameters is defined to perform a set of finite element computations. The sensitivity analysis is focussed on nucleation and growth of microvoids; the related modifications on microvoid volume fraction, effective plastic strain, hydrostatic stress, dimensions, and load are given through two reference models, the tensile test of a single axisymmetric Q4 element and the upset of a clamped cylinder.

It is shown that refined analysis requires the determination of four supplementary material parameters, the initial microvoid volume fraction, the effective plastic strain at incipient nucleation, the potential nucleated microvoid volume fraction consistent with the inclusion volume fraction and the Gaussian standard deviation of inclusions distribution. Nevertheless, for large plastic strain occurrences, an accurate identification of the effective plastic strain at incipient nucleation and the standard deviation of inclusions distribution parameters is not necessary.
Damage in a [0/90]2s Nicalon-Reinforced CAS Glass Ceramic Composite
Authors: Soboyejo W. O. , Ramasundaram P. , Goettler R.
Published: July 2008

The results of an experimental investigation of damage in a symmetric 12-ply nicalon-reinforced calcium alumino-silicate (CAS) composite are reported. The initiation and evolution of damage under monotonic and cyclic loading is monitored using optical and scanning electron microscopy, compliance, and acoustic emission techniques. Damage thresholds are established for monotonic and cyclic loading conditions, and the bulk levels of damage are characterized using a modulus-based damage parameter.
The Variation of the Elliptic Paraboloid Failure Locus Beyond the Elastic Limit
Authors: Theocaris Pericles S.
Published: July 2008

A method is presented by defining an isotropic hardening plasticity through an appropriate sequence of an isotropic problems. Assuming a stepwise form of loading or unloading, we measure the instantaneous tension and compression yield stresses along the transient principal-stress directions. These parameters completely define the instantaneous state of anisotropy of the body for the corresponding loading step, by applying the theory of elliptic paraboloid failure locus (EPFS). The parameter identification problem is formulated on the constitutive expressions for this most general failure criterion, and by applying convenient constraints derived from the EPFS theory, which are serving as filters throughout the whole procedure of evaluating the characteristic values of terms defining the variable components of the failure tensor polynomial, as the material is continuously loaded from the elastic into the plastic region and up to the ultimate failure load.

Accurate simple tests in uniaxial tension and compression yield sufficient data for defining the yield loci of the material for the loading step considered. These data were used as input values for establishing the mode of plastic deformation of the body during a particular loading path. It was shown that the prediction or the eventual correction of either extrapolated or interpolated yield surfaces are reasonable and concordant with experimental evidence.

Since the method allows the separate complete definition of the particular values of the coefficients of the failure tensor H and the strength differential effect tensor h at each loading step, it presents the important advantage over other experimental methods of clearly indicating the parts contributed either by plasticity, or by strength differential effect of elastically and plastically deformed materials and their evolution during the development of plastic deformation.
Prediction of Plane-Strain Creep-Crack Growth Using Continuum Damage Mechanics
Authors: Hall F. R. , Hayhurst D. R. , Brown P. R.
Published: July 2008

The paper examines the possibility of using creep Continuum Damage Mechanics to predict plane strain creep crack growth in compact tension specimens using finite element based numerical methods, coupled with uni-axial and multi-axial stress laboratory creep data, and with mechanisms-based constitutive equations. The predictions of the behaviour of the compact tension specimens made using the single state damage variable equations due to Hayhurst, Dimmer, and Morrison (1984) are shown to be unable to predict that zones of damage do not grow in discrete planar regions as observed in laboratory experiments.

To overcome the deficiencies of this approach, new constitutive equations have been developed, which combine the equations of Hayhurst et al. (1984) with those of Cocks and Ashby (1982), to describe the stress-state dependence of the physical mechanisms. The behaviour of the compact tension specimen determined using these new equations predicts lifetimes of the correct order and evolution of damage zones which reflect the growth of discrete cracks as observed experimentally.

The paper shows that creep Continuum Damage Mechanics can be used with finite element based numerical procedures to predict creep crack growth, provided that mechanisms-based constitutive equations are used which describe the appropriate stress-state behaviour for each mechanism zone, and that continuity of mechanical properties are achieved across all mechanism boundaries.
A Model of Anisotropic Damage by Mesocrack Growth; Unilateral Effect
Authors: Halm Damien , Dragon André
Published: July 2008

A three-dimensional model of anisotropic damage by mesocrack growth is first described in its basic version, employing a second-order tensorial damage variable. The model—concerning rate-independent, small strain, isothermal behaviour—allows to take into account residual effects due to damage and reduces any system of mesocracks to three equivalent orthogonal sets. This first version is then extended to account for elastic moduli recovery due to crack closure. Micromechanical considerations impose to employ a fourth-order crack-related tensor when the mesocracks are constrained against opening. Unlike some models which do not avoid (or rectify a posteriori) discontinuities of the stress-strain response, the approach herein ensures a priori the stress continuity and allows to express a convenient macroscopic opening-closure criterion. Nevertheless, the new formulation maintains the orthotropy of the effective properties (instead of an eventual, more general form of anisotropy). Finally, it appears that the extended version does not introduce additional material constants compared to the basic version. The model is tested by simulating the behaviour of Fontainebleau sandstone.
Shear Band Initiation of Brittle Damage Materials
Authors: Sun Xin , Wimmer Stephanie A. , Karrt Dale G.
Published: July 2008

Some effects of material degradation on failure mechanisms of brittle damage materials are investigated. Conditions for the localization of deformation within a shear band are established for rate independent damage materials. In contrast with previous work on shear band initiation that relied on plasticity and flow theory formulation, the present study finds it sufficient for the shear band to emerge in the regime of infinitesimal strain for brittle damage materials. Bifurcations from the homogeneous deformation mode in the form of shear bands are captured for loading conditions of plane strain compression and uniaxial compression using conventional continuum damage mechanics formulations. The inclination angle and critical strain for shear band initiation are calculated using well-established mathematical theory. A finite element simulation of shear band initiation for a rectangular mesh deformed in plane strain compression is also presented.