高应变率下NiTi合金动态力学行为及变形机理研究

NiTi合金是一种典型的、具有优异物理力学性质的形状记忆合金，在微秒、纳秒量级瞬态载荷环境中被广泛应用，如航天器吸能部件、防护盔甲等。实验上对NiTi合金在应变率1e4/s以上能否发生应力诱导马氏体相变还存在争议，尤其缺乏应变率1e4/s -1e7/s范围NiTi合金动态宏观力学性能、微结构演化及其变形机理系统研究。本项目拟采用磁驱动加载实验技术实现跨量级的高应变率加载，获得应变率1e4/s -1e7/s范围内NiTi合金应力诱导马氏体相变压力、母相屈服强度等典型的宏观力学性能及其率效应。结合样品回收和微结构表征技术，获得不同应变率下NiTi合金晶体结构、晶体取向、织构等典型微结构特性。建立适用于高应变率的NiTi合金多物理机制晶体塑性本构模型，获得高应变率加载下NiTi合金微结构演化规律及其形成机理，为揭示形状记忆合金材料动态响应规律及拓宽其在工业、国防领域应用奠定坚实基础。

NiTi alloy is a typical shape memory alloy with excellent physical and mechanical properties. It has been widely used in transient loading environments on order of microseconds or nanoseconds, such as energy-absorbing components of spacecraft and protective armor, and so on. There is still controversial for NiTi alloy whether the stress-induced martensite transformation happens at strain rate above 1e4 /s. And the investigations on dynamic macroscopic mechanical properties, microstructure evolution and deformation mechanism of NiTi alloy were insufficient especially at strain rate range from 1e4 / s to 1e7 /s. In this project, the magnetically driven techniques are used for achieving loading over several orders of high strain rate. The phase transition pressure of stress-induced martensite transformation and yield strength of austenite NiTi alloy are studied experimentally at strain rate range from 1e4 / s to 1e7 /s. In addition, typical microstructure characteristics such as crystal structure, crystal orientation and texture of NiTi alloy at different strain rates are obtained by sample recovery and microstructure characterization techniques. A physical based crystcal plasticity constitutive model of NiTi alloy for high strain rate is developed for obtaining mesoscopic microstructure evolution and deformation mechanism. The findings in this work will lay a solid foundation for revealing the dynamic responses of shape memory alloy and broadening the industrial and defense applications.