基于晶体塑性理论研究铝材料高压高应变率下的强度特性

On strength of aluminum under high pressure and high strain rate based on crystal plasticity theory

为了了解金属材料在极端加载下复杂动态响应过程中的多种机制和效应,重点针对Al材料在高压、高应变率加载下的塑性变形机制,在经典晶体塑性模型的基础上,对其中的非线性弹性、位错动力学和硬化形式进行改进,建立适用于高压、高应变率加载下的热弹-黏塑性晶体塑性模型。该模型可以较好地描述单晶铝和多晶铝材料屈服强度随压力的变化过程,相比宏观模型,用该模型还获得了多晶Al材料在冲击加载下的织构演化规律,揭示了织构择优取向行为和压力的关系。

Dynamic behaviors of metal materials are very complex under extreme loading conditions such as high pressure and high strain rate loading. Actually, many mechanisms and effects are contained in the dynamic response of metal materials. In this paper, a thermoelastic-viscoplastic crystal plasticity model is developed to study the plastic deformation of aluminum (Al) materials under high pressure and high strain rate loading. In the model for single crystal, both the thermally-activated mechanism and the phonon drag mechanism are considered for dislocation glide which make the model applicable for a much wide deformation rate range. In addition, the density of the mobile and immobile dislocation is formulated according to the annihilation and multiplication mechanism. A general harden model is utilized to take strain harden, pressure harden and temperature soften into consideration. Moreover, a high-order Euler elastic equation is adopted to describe the non-linear elastic deformation of the materials in large elastic deformation. Furthermore, based on the model developed for single crystal plastic deformation, a polycrystalline model is developed according to the Taylor model and the crystal plasticity finite element method, respectively. The dislocation glide speed in Al materials is predicted by the model and the results agree quite well with the experimental results in a wide shear stress range because both thermally-activated mechanism and phonon drag mechanism are considered for dislocation glide. With the model, the shear strengths of both single crystal and polycrystalline are predicted, and it is found out that the shear strength of Al materials increases with increasing of the load pressure. Besides, significant anisotropy of the shear strength is revealed for single crystal Al materials although it is a typical FCC crystal with high symmetry. Finally, texture evolution of polycrystalline Al materials is studied with the model and the preferred orientation effect of the crystal is found for different loading pressures. Moreover, the preferred orientation effect is more significant for high loading pressure.