CREEP CONSTITUTIVE EQUATION AND EXPERIMENTAL DETERMINATION OF COMPOSITE MATERIALS Part Ⅰ.Constitutive Equaiton

Creep is one of the most important mechanical behaviors of composite material.The results of creep-recovery experiments show that under creep condition deformation can be divided into three parts:elastic deformation,viscoelastic deformation which can recover slowly and viscoplastic deformation which cannot when the load is removed.The thermodynamics of irreverible processes and concept of generalized variables can be used to derive creep constitutive equation in which strain is expressed observable variable.In this paper,the foundamental thermodynamics equationw arc reviewed.Based on the assumption,and idea of Schapery's equation,the common formula of mufti-dimensional creep constitutive equation is derived which includes elastic,viscoelastic and viscoplastic deformations.Considering that the generalized force is not unique,the authors proposed a principle for selecting variables so that the result is as simple as possible.According to such a principle,some special constitutive equations presented,which include the equations for one-dimensional problems,twodimensional problems of the isotropic material and the plane problems of fibre reinforced composite materials.