聚酰亚胺的动静态压缩力学性能及本构模型

To study the mechanical properties of polyimide, quasi-static and dynamic compression experiments were carried out using the materials testing system (material testing system, MTS) and the split Hopkinson pressure bar (SHPB). The stress-strain curves of the material under different strain rates were obtained. The morphology of the recovered specimens was analyzed, and the characteristics of the polyimide in terms of crack form and size deformation were obtained. A bilinear relationship between the dynamic increase factor of the polyimide and the strain rate was obtained. The bilinear characteristics were described by piecewise fitting model and Cowper-Symonds model. Based on the characteristics of the dynamic mechanical response of the polyimide, its compression deformation mechanism from low to high strain-rates was explained. A phenomenological constitutive model in consideration of the contributions of the β-transition was modified to describe the large elastic-plastic deformation response of the material, in which initial viscoelasticity, yield, strain softening and strain hardening were all included. Then the constitutive model’s parameters were fitted by Bayesian approach. The Bayesian fitting results at different strain rates were in good agreement with the experimental data.