极高应变率载荷下金属材料表面动态损伤破坏机理及过程诊断基础研究

New methods and techniques will be developed in this grant application to detect quantitatively the process on the surface of metal materials under the loading by femtosecond laser, as well as the evolution of transmission properties of laser-induced shockwave. The kinetic parameters and spectral characteristics at the beginning of the loading process by femtosecond laser on the workpiece surface will be diagnosed with the methods of transient intensified CCD camera and laser-induced breakdown spectroscopy. The techniques of laser multifrequency Raman generation, chirped pulse spectrum interference and optical spectral phase coherent reconstruction will be utilized to obtain the transmission properties of the shockwave in the wokpiece and evolution process of characteristic parameters on the free-surface of femtosecond magnitude under ultra-high strain rate loading. On this basis, a systme will be established to diagnosed dynamically the process of damage and fracture of metal surface under ultra-high strain rate loading. Study will also be carried out on the loading characteristics of femtosecond laser-induced shockwave, the caused property conversion to the material, and the changes of micro-metallurgical-structure under ultra-high strain rate loading. Then, molecular dynamical property of stress wave and its evolution in the metal material will be explored to find out the developing rules of mechanical effects induced by femtosecond laser shockwave during the process of laser loading. At last, the theory of structural defects of the material for femtosecond laser loading will be built, the dynamic damage and fracture properties and mechanisms of metal surface will obtained under ultra-high strain rate loading, which can be applied to calculate the dynamic damage and fracture of metal surface and its process diagnosis under ultra-high strain rate loading.

发展飞秒激光在金属材料表面上的加载过程以及激光冲击波的传输特性演化的定量探测，利用基于增强型信号探测器成像与激光诱导击穿光谱技术诊断飞秒激光加载工件表面的初期动力学参数与光谱特性，基于激光多频拉曼散射、啁啾脉冲频谱干涉和光学位相相干解包重建技术获取飞秒量级极高应变率载荷下工件内部冲击波传输及材料自由面特征参量的过程演化特性，建立相应的超高应变率载荷下金属材料表面损伤破坏过程的动态诊断系统。研究飞秒激光冲击金属材料极高应变率载荷下的激光冲击波具体加载特性及其对材料产生的性能转化以及微观金相组织结构变化，探索飞秒激光加载下材料内部应力波分子动力学特性及其演化过程，获取飞秒激光高压加载金属材料过程中的激光冲击波力学效应发展规律。拓展激光冲击载荷作用下的材料缺陷结构理论，获得极高应变率下金属材料的损伤破坏特性及机理，实现飞秒激光极高应变率载荷下金属材料表面动态损伤破坏的理论计算及其过程的诊断。

本项目对激光加载引起的超高应变率下的层裂过程进行了研究。基于有限元计算软件，对激光加载下的金属层裂行为进行了有限元仿真研究，建立了激光加载下的不同厚度的靶材模型，探讨了高能激光致层裂与靶材厚度的关系，并对比了纳飞秒激光与钛合金属的作用表现差异；基于模型处理软件和分子动力学模拟软件，对飞秒激光与材料相互作用的双温方程进行改进，对飞秒激光加载下的材料表面层裂行为进行分子学动力分析，探索了飞秒激光加载下的形状记忆合金微观热效应体系，得到合金表面电子与晶格温度体系变化规律、电子-晶格平衡温度、激光脉宽对材料加载的影响规律。采用S.I.Anisimov经典双温方程探索飞秒激光加载下的金属合金微观热效应体系，使用有限差分法从脉宽条件、能量密度与电子晶格体系平衡温度方面研究了金属钛合金的微观热效应性质。通过将材料内部离子与电子温度分别处理得到的电子-晶格平衡温度对为分子动力学模拟提供更好的加载温度；利用双温方程求得的电子-晶格平衡温度作为温度输入，采用合适势函数，进行飞秒激光加载下的钛合金的分子动力学模拟与实验，分析了微观下空洞成核生长等现象，对合金表面层裂机理的研究分析有很好的指导作用。