Lattice Deformation Measurement under Shock Wave Loading by Pulsed X-ray Diffraction

Abstract

Shock of condensed matter is ubiquitous in nature, yet a full understanding of the response when shock waves propagate into solids is still lacking because of a lack of real-time microstructural data. Pulsed X-ray diffraction technique is being developed as a microscopic lattice diagnostic technique for shocked crystals, and it can provide transient information of lattice structure from the shock front. In this thesis, a pulsed X-ray diffraction measurement system was established by using a molybdenum-target miniaturized flash X-ray source with the half width of 25 ns and digital X-ray photography equipment. Real-time measurement of lattice response under one-dimensional strain loading was realized, and useful information for understanding the response of shocked solids was acquired using this system. The model of pulsed X-ray diffraction measurement of lattice deformation rate was established. The influence on X-ray diffraction measurement from impact tilt and translation of the crystal sample was analyzed and the quantitative data correction method was proposed. The uncertainty analysis method was implemented and uncertainty of lattice deformation rate including all kinds of uncertainty factors was obtained. The pulsed X-ray diffraction measurement system built was used to study the lattice response of shocked LiF single crystals under one-dimensional strain loading experiments based on the one-stage gas gun loading experimental platform. Single pulsed X-ray diffraction data from LiF single crystals were obtained when loading along the ［100］ direction. In the experiment, the initial input stress obtained in sample was 3.65 GPa. The reflected stress from the LiF/back-plane interface was reduced to 2.33 GPa. In the experimental data, two shocked diffraction peak has appeared. The experimental results show that reflected rarefaction wave was moving back through the LiF crystal during Xray exposure time. The LiF crystal ahead of the rarefaction wave front was in one shocked state, while the LiF crystal between the rarefaction wave front and the LiF/backplane interface was in another shocked state. Quantitative measurement of lattice deformation related to shock pressure (233 Gpa and 365 GPa) was achieved, and the lattice deformation results measured are in agreement with the calculated results from Hugoniot relation. The results reveal an isotropic compression of the unit cell in shocked plastic deformation of LiF(100). The present work has provides an effective means to study the microscopic lattice response under shock compression experiment. However, further work is needed when using diffraction methods to a broader range of problems. For example, time resolution can be enhanced with a brighter X-ray source, and continuum measurement can be conducted to accurate the relationship between the continuum response and microscopic lattice response.

Keywords

• pulsed x-ray
• shock wave loading
• lattice deformation
• x-ray diffraction