Ganesh Thiagarajan

An anisotropic yield surface model for directionally reinforced metal-matrix composites

A new six parameter general anisotropic yield surface using a fourth order anisotropic tensor Mijkl has been proposed. This form has been derived based on the physical behavior observed for the material under consideration — directionally reinforced metal matrix composites. Its validity has been shown by proving its convexity and form under coordinate transformation. This form of the anisotropic yield function is general in nature which can be used for either pressure dependent or independent cases. By applying suitable conditions on the parameters, it can be reduced to the von-Mises and Tresca isotropic yield criteria. It can also be reduced to specific anisotropic models such as Hills [1948 “A Theory of the Yielding and Plastic Flow of Anisotropic Metals,” Proceedings of Royal Society of London, A193, 281–297] pressure independent anisotropic yield function form and the Mulhern, Rogers and Spencer [1967 “A Continuum Model for a Fiber Reinforced Plastic Material,” Proceedings of Royal Society of London, A301, 473–492] pressure independent yield criterion for transversely isotropic materials, which is used for the continuum description for yielding in metal-matrix composites. The proposed surface compares well with the extensive experimental data of Dvorak et al. [1988 “An Experimental Study of Elastic-Plastic Behavior of a Fibrous Boron-Aluminum Composite,” Journal of the Mechanics and Physics of Solids, 36, 655–687] and Nigam et al. [1993 “An Experimental Investigation of Elastic-Plastic Behavior of a Fibrous Boron-Aluminum Composite. I. Matrix-Dominated Mode,” International Journal of Plasticity, 10, 23–48] performed on boron-aluminum metal-matrix composite. Based on the experimentally observed flow and hardening behavior, the elasto-plastic stiffness matrix has been proposed.

A cyclic anisotropic-plasticity model for metal matrix composites

Based on a six parameter general anisotropic yield surface proposed earlier by Voyiadjis and Thiagarajan (An Anisotropic Yield Surface Model for Directionally Reinforced Metal Matrix Composites, Int. J. Plasticity [1995]), a cyclic plasticity model to model the behavior of directionally reinforced metal matrix composite, has been proposed here. Apart from being able to model different initial yielding behavior along different stress directions, a number of features have been incorporated into the plasticity model. They include the usage of a proposed non-associative flow rule, kinematic hardening rule of Phillips type, a modified form of the bounding surface model for modelling the cyclic behavior, and the usage of a proposed form for evaluating the plastic modulus for anisotropic materials. Previous experimental data have been used for the evaluation of the yield surface parameters as well as those for the determination of the plastic modulus. The stress-strain results generated from the model have then been compared with those from the experiments. The behavior of the model under certain simulated cyclic loading situations has also been presented.

Micro and macro anisotropic cyclic damage-plasticity models for MMCS

Abstract Two approaches to modeling the cyclic damage-plasticity behavior of metal matrix composites are presented in this paper, namely: a micro (micromechanical-damage) and a macro (continuum-damage) based approach. Each of these approaches involves a fictitious undamaged ‘effective’ configuration to which the plasticity equations are applied and constitutive equations derived. Using the equations for the transformation of stress from the undamaged to the damaged configuration, the transformation of these equations to the actual damaged configuration is performed. Two new concepts are introduced here: (i) the incorporation of a term ϒ, similar to backstress, in the thermodynamic force Y space in the cyclic damage criterion, and (ii) the concept of cyclic damage under cyclic loading situations. This paper outlines the results from the two models in comparison with experimental results and compares and contrasts the effectiveness of the two models.

A damage cyclic plasticity model for metal matrix composites

Publisher Summary This chapter presents a mathematical model to simulate the behavior of metal matrix composites under cyclic proportional and nonproportional loading. This model incorporates both the phenomena of damage and cyclic plasticity. In the chapter, a description of the cyclic plasticity model is presented and based on this model the development of the damage based plasticity model is outlined. The cyclic plasticity model is based on an anisotropic yield criterion. The salient features of this criterion are outlined in the chapter along with some experimental comparisons. The model uses a nonassociative flow rule and a modified form of the bounding surface model, for the case of anisotropic materials. This procedure involves the computation of the anisotropic plastic modulus. All materials undergo damage that is synonymous with the degradation of the materials elastic stiffness as repeated loading takes place. To account for this phenomenon, a damage-plasticity model is presented in the chapter. This is based on the cyclic plasticity behavior blended with the damage model.

A cyclic plasticity model for metal matrix composites

In this paper the metal-matrix composite(MMC) is treated as a transversely isotropic continuum material. A six parameter general anisotropic yield surface had been proposed earlier by the authors (1995a) has been adapted to continuous unidirectionally reinforced MMC’s. In this work a model is proposed, using the yield surface proposed earlier to describe the behavior of MMC’s subsected to cyclic, proportional as well as non-proportional loadings. The cyclic model is based on the modifications of the bounding surface model proposed by Dafalias And Popov [1976].

A cyclic plasticity model for metal-matrix-composites using an anisotropic yield surface

ABSTRACT A cyclic plasticity model is proposed here to predict the behavior of directionally reinforced metal matrix composites. A six parameter general anisotropic yield criterion is proposed and used here. This anisotropic plasticity model uses a non-associative flow rule, a kinematic hardening rule of Phillips type and the usage of a modified form of the bounding surface to model cyclic behavior. Also a new form for evaluating the plastic modulus for anisotropic materials is proposed here. The experimental data of Dvorak et. al. (1988) and Nigam et. al. (1993) have been used in the evaluation of the various parameters, and for comparison of results.