INFLUENCE OF THERMAL ESTRESS.pdf
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Ž . Mech anics of Ma teri als 2 7 1998 229–240 Influence of thermal residual stresses on the composite macroscopic behavior G.K. Hu a,b, ) , G.J. Weng c a Department of Applied Mechanics, Beijing Institute of Technology, Beijing 100081, China b LNM Institute of Mechanics, Academia Sinica, Beijing 100080, China c Department of Mechanical and Aerospace Engineering, Rutgers Uni Õersity, New Brunswick, NJ 08903, USA Received 4 June 1997 Abstract The influence of the thermal residual stress on the deformation behavior of a composite has been analyzed with a new micromechanical method. The method is based on secant moduli approximation and a new homogenized effective stress to characterize the plastic state of the matrix. It is found that the generated thermal residual stresses after cooling and their influence on the subsequent deformation behavior depends significantly on the aspect ratio of the inclusions. With prolate inclusions, the presence of thermal residual stresses generate a higher compressive hardening curves of the composite, but it is reversed with oblate inclusions. For particle reinforced composite, thermal residual stresses induce a tensile hardening curve higher than the compressive one and this is in agreement with experimental observations. q 1998 Elsevier Science Ltd. Keywords: Metal matrix composite; Residual stress; Micromechanics; Second order stress moment; Plastic strain 1. Introduction Due to a mismatch in the coefficients of thermal expansion between the matrix and inclusions, change in temperature produces an internal stress in the composite. These thermal stresses may be partially relaxed by the Ž plastic defo rmatio n of the ductile matrix and lead to additi onal harde ning of the matrix in the compo site Taya . and Mori, 198 7; Shi bat a et al. , 1992; Ramakr ishnan, 1996 . Since the thermal eff ect s are ind uced bef ore mechanical testing, their presence can induce the asymmetry in the tensile and compressive yield stresses of the Ž . compo site Arsenau lt and Taya, 1987 ; Corbin et al., 1991 . Because of its influence on the properties, the residual stress in composites has been the subject of several Ž . studie s, both experimentall y and analyti cally. The equ ivalen t inclusion method Eshelb y, 1957 is usually used Ž . to evaluate ther mal residua l stresses of a compo site Takao and Taya, 1985 ; Withers et al., 1989 . The average state of the internal stresses in the matrix can be readily calculated. A simple way to analyze the plastic behavior ) Correspondi ng author. 0167-6636r98r$19.00 q 1998 Elsevier Science Ltd. All rights reserved. Ž . PII S0167-6636 97 00050-1
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