超高应变率载荷下铜材料层裂特性研究  

Spall behavior of copper under ultra-high strain rate loading

作　　者：席涛[1] 范伟[1] 储根柏[1] 税敏[1] 何卫华[1] 赵永强[1] 辛建婷[1] 谷渝秋[1] 

机构地区：[1]中国工程物理研究院激光聚变研究中心,等离子体物理重点实验室,绵阳621900

出　　处：《物理学报》2017年第4期8-15,共8页Acta Physica Sinica

基　　金：中国工程物理研究院重点实验室基金(批准号:9140C680306150C68298,9140C680305140C68289)资助的课题~~

摘　　要：超高应变率载荷下材料层裂特性研究对理解极端条件下材料动态破坏特性具有重要意义.利用双温模型结合分子动力学模拟研究分析了超高应变率载荷下铜材料的层裂特性,发现当应变率在10~9s^(-1)—10^(10)s^(-1)内时,铜材料层裂强度在19 GPa附近波动.而当材料发生冲击熔化时,铜的层裂强度下降到14.89 GPa.利用飞秒激光对铜样品靶进行冲击加载,并利用啁啾脉冲频谱干涉技术开展超快诊断,通过单发次实验测量获得了样品靶的自由面粒子速度演化历史,结果未见表征样品层裂的速度回跳和速度周期性振荡信号.结合冲击动力学理论得到样品自由面附近最大加载压强为8.18 GPa,小于超高应变率载荷下铜材料的层裂强度.此外,对回收样品扫描分析发现,铜样品未发生层裂且飞秒激光引起的冲击波对样品表面结构产生了很大影响.The spall behavior of copper at ultra-high strain rate is studied by molecular dynamics simulation combined with an experimental analysis of laser ablation of a bulk copper target by femtosecond laser pulses. In the molecular dynamics simulation, two-temperature model is used, shock wave and spallation characteristics of copper shock-loaded by femtosecond laser are analyzed in detail. It is concluded that the evolution of pressure indicates a triangular waveform of the shock wave, and the spall strength of copper is about 19 GPa at strain rates ranging from 109 s-1 to 1010 s-1, while higher pressure would melt the sample and the spall strength decreases to 14.89 GPa. Normally, the spallation is characterized by the sample free-surface undergoing alternately acceleration and deceleration, and the spallation mechanism could be explained by void nucleation, growth, coalescence that leads to the final fracture. An experiment is conducted to achieve high strain rate load on copper. The driving laser has a pulse width of 25 fs and central wavelength of 800 nm, the thickness values of the shocked copper foils are （502±5） nm, fabricated by electron beam sputtering deposition onto 180 μupm cover slip substrates. The driving laser beam with maximum intensity 5.5×1013 W/cm2, is focused on the front surface of the copper through the transparent substrate. Movements of the free rear surfaces of the copper foils are detected by chirped pulse spectral interferometry, and the theoretical time resolution is 1.3 ps. As a result, the free surface displacement and velocity evolution profile of the shocked area are obtained in a single measurement, and the results directly show that the maximum free surface velocity is 0.43 km/s and no alternately acceleration and deceleration appears. According to the shock wave relations, the maximum pressure near free-surface is 8.18 GPa. Meanwhile, derived from the velocity evolution profile, the strain rate is 7.3×109 s-1. Combining with the above molecular dynamics simulation results, i

关 键 词：层裂 超高应变率 分子动力学模拟 频谱干涉 

分 类 号：TG146.11[一般工业技术—材料科学与工程]