[100]LiF单晶在60 GPa以内冲击加载下的高压屈服强度特性

获取光学窗口自身的高压强度特性是开展材料高压高应变率冲击响应行为精密测量和数据反演的重要基础。利用平板撞击和双屈服面法，通过冲击-卸载、冲击-再加载原位粒子速度剖面精细测量和数据反演，获得了约60 GPa范围内100]LiF屈服强度特性随冲击压力的变化规律。结果表明:在实验压力范围内，100]LiF的屈服强度随加载压力的提高而显著提高，压力硬化效应显著；同时，LiF在冲击加载下的屈服强度高于磁驱准等熵加载结果，应变率硬化效应强于热软化效应。采用Huang-Asay模型确定了可描述冲击加载100]LiF强度特性的本构模型参数，为LiF在强度、相变、层断裂等加窗测量实验中的深入应用和数据准确解读提供了重要支撑。

Yield strength of [100] LiF under shock compression up to 60 GPa

The dynamic properties of metals are of importance in shock wave physics, and the time-resolved velocity profile measurement at the interface between the sample and the optical window is often used to decrease the waveform aberrations arising from free-surface reflecting and to obtain the in-situ particle velocity profile in the studied sample. In such cases, the yield strength behavior of the optical window should be taken into account for precise data processing. Among kinds of optical window materials, 100] lithium fluoride (LiF) single crystal is the most widely used window, and little work has been done for its yield strength behavior under dynamic loadings, especially planar shock. In this paper, by using the plate impact and Asay self-consistent technique for high-pressure yield strength, in-situ velocity profiles of the 100] LiF single crystal from shock-release and shock-reshock loading at different pressures were carefully measured by a displacement interferometer system for any reflector (DISAR). Then, the yield strengths under shock compression up to about 60 GPa were educed and found to markedly increase with the increasing of shock pressure, showing a notable pressure-hardening effect. Moreover, by comparing with the results from magnetically-driven isentropic loading in literatures which were the scanty public reports for the high-pressure yield strength of LiF, it was also found that the yield strengths of the 100] LiF under shock compression were higher than those obtained from isentropic loading at the same pressures. This indicates that LiF’s yield strength is more sensitive to strain rate than to temperature up to 60 GPa, and the higher strain rate under shock compression and the dominant strain rate hardening effect results in a higher yield strength. At last, the constitutive model parameters for the 100] LiF were determined to fit to our shock experiments well by using the Huang-Asay equation form. The result above shows that the 100] LiF owns an unignorable flow strength under shock pressures at least to 60 GPa. Moreover, it provides important constitutive parameters for educing the in-situ velocity profiles more accurately in experiments where LiF is used as an optical window, which is essential for researches such as flow strength, phase transition, and shock melting of metal materials.