Numerical techniques for elastic-plastic analysis of fibrous metal matrix composites.

摘要

The development of metal matrix composite material model routines for elastic-plastic finite element procedures is presented. Three constitutive formulations including strain-space & strain-controlled input, stress-space & stress-controlled input, and stress-space & strain-controlled input, are implemented into a general purpose finite element program (ABAQUS (1985,1986,1988a,b)). Computationally efficient algorithms are derived for the stress-space, strain-controlled constitutive models. The micromechanical models considered in this work are the following: (1) Strain-space, strain-controlled Vanishing Fiber Diameter (VFD) model of Bahei-El-Din & Dvorak (1979,1982) and Wung & Dvorak (1985) (preliminary work only). (2) Stress-space, stress-controlled Periodic Hexagonal Array (PHA) model of Dvorak & Teply (1985) and Teply & Dvorak (1988). (3) Stress-space, stress-controlled and stress-space, strain-controlled bimodal plasticity theory of Dvorak & Bahei-El-Din (1987) and Bahei-El-Din & Dvorak (1989,1991).; The material routines developed are used for the dimensional stability analysis of the {dollar}(pmphi)sb{lcub}rm s{rcub}{dollar} composite laminates. In the dimensional stability study, the explicit form of the composite constraint hardening vector (i.e. the hardening due to thermal effects) is derived based on the laminate theory and decomposition procedure (Dvorak, 1986). The constitutive calculation of the laminate is performed with the finite element method while the underlying constitutive equations of unidirectional composites are provided by the PHA model. The dimensional stability of the {dollar}(pmphi)sb{lcub}rm s{rcub}{dollar} laminates due to thermomechanical cycles or heat treatment is investigated. It is shown that the {dollar}(pmphi)sb{lcub}rm s{rcub}{dollar} laminates are not in general dimensionally stable. The thermal and mechanical loads affect the dimensional stability of the {dollar}(pmphi)sb{lcub}rm s{rcub}{dollar} laminate significantly.; Finally, a study on the local fields of coated and uncoated composites are performed using ABAQUS. The first part of the study presents a detailed evaluation of the local fields in B/Al and T50 Gr/Al fibrous composite systems under various loading conditions. It is shown that the stress distributions in both systems have certain common features and also have some individual differences. The second part of the study addresses the question of accuracy of averaging models in analysis of inelastic composites. It is shown that the local fields of the composite vary pointwise in the plastic range and the use of averaging methods for prediction of composite overall properties may be unreliable. The third part of the study presents the local fields of coated and uncoated SCS6/Ti3Al and SCS6/Ni3Al composite systems produced by various manufacturing processes. The results show that, due to the change of relative stiffness between coating material and matrix material, the coating material is important to the composites only during the early stage of the loading history (i.e. when the matrix is in elastic range) whereas the plasticity parameters (i.e. yield stress and plastic tangent modulus) of the matrix are important when the composite is loaded to fully plastic stage.