高分子材料注塑固化阶段的残余应力分析

在结晶性高分子材料注塑过程的固化阶段，温度分布、材料细观结构和应力应变之间相互耦合，因而其变化规律非常复杂．本文在井上等人考虑材料细观结构变化的金属热加工工艺应力分析［３～６］的基础上，发展了一套用于高分子注塑固化阶段残余应力分析的本构描述和有限元分析方法．在本构模型中，同时考虑了温度变化、结晶和“冻结取向”对变形的贡献．

CALCULATION OF RESIDUAL STRESSES IN INJECTION MOLDED PRODUCTS FOR POLYMER MATERIALS 1)

Temperature distribution, microstructure of materials and stress strain are known to change in a complicated manner during mold cooling of semicrystalline thermoplastic polymers due to the coupling effects between them. These complex interaction and the factors which will induce the deformation in the final product, such as temperature variations, cry stallization and frozen in orientation are carefully discussed in the first part of this paper. The cons titutive relations of the thermoelastic plastic bodies during mold cooling stage when considering crystal lization and frozen in orientation are built on the basis of continuum thermodynamics. Interaction between temperature and crystallization structure is also discussed to obtain the heat conduction equation including latent heat due to crystallization. The model doesn't deal with the non Newtonian fluid flow directly but calculate the flow induced residual stresses by investigating the microstructure of polymer materials after filling and postfilling stage and establish the relation between the strain and the microstructure .This kind of microstructure is called frozen in orientation, which can be described by the birefringence distribution in injection molded products. Application of the theory to a simple case of slab injection is also presented. Temperature and residual stresses distributions are numerically calculated by a finite element technique after determining the physical properties from the dynamic equation of crystallization. The data of birefringence distribution in the injection molded products come from the experiment. So the distribution of frozen in orientation at the beginning of mold cooling are known initial conditions in the analysis. In can be obtained from the analytic results that the temperature of melt drop rapidly during the beginning of mold cooling, and it slow down in the later. However, at the same period, the variation of the stresses are obviously. It means crystallization and frozen in orientation contribute a lot to the residual stresses. The results indicate that the polymer materials near the surface of the products always endure severe tension, which are easy to induce craze or even cracks in the surface. So it should take measures to make the crystallization and frozen in orientation to distribute more even in the products. WT10.75HZ]