With Gas-solid Mixture Of The Macroscopic Constitutive Relation Of Composite Materials Research

Microcellular foam plastics made by the new physical foaming technics has developed very quickly and becomes one of the host study regions in recent years. This paper is concerned with the macroscopic constitutive relations of the microcellular foam plastics with considering the internal pressure of bled.Firstly, a new nonlinear visoelastic constitutive model is proposed which can adequately describes observations in the Polypropylene-unaxial tensile tests. According to the concept of "elastic related material", the nonlinear visoelastic stress-strain relation is linearized.Secondly, the strain of single air bleb in the infinite matrix is studied under the different loading conditions. With the increment method, a differential expression of the bled strain is derived, in the expression, the bled strain can be expressed by the void pressure and Poisson's ratio of matrix. The numerical results show that the influence of the pressure on the void strain is so small that it can be neglected, and the influences of Poisson's ratio and configuration of the bled are both related to the loading condition.Thirdly, by means of the Eshelby-Mori-Tanaka method, the macroscopic constitutive relation is derived, and it can be expressed by the-void pressure, voidfraction, the initial stress of matrix and loading rate. Numerical results indicate that, thestrength per unit volume of the matrix doesn't change with the void fraction under the uniaxial loading, but declines with the void fraction under the uniaxial strain loading. The initial stress of the matrix caused by the void pressure reduces the effective tensile performance of composite. The influence of Poisson's ratio of matrix and the rate of loading on overall constitutive relations are also discussed under different loading conditions by the numerical method.Finally, the effect of atmospheric pressure on the interfacial debonding inparticulate-reinforced rheological materials is studied. Based on an energy criterion, a simple formula of local critical stress for interfacial debonding is derived, and it can be expressed by interfacial adhesive energy, particle radius and atmospheric pressure. An equation describing critical time of interfacial debonding is formulated.Compared with other researches, there are two main characteristics in this paper. One is that the matrix of the composite is a nonlinear visoelastic material, the other is the internal pressure of bled is considered when the strain of bled and the macroscopic constitutive relations of composite are analyzed.The present work may be used to supply some guidelines for the design of Microcellular foam plastics.