Design, testing, and utilization of a spherical shock-recovery system to investigate material response to ultrahigh pressure

The existing shock recovery systems can be classified as planar or convergent. Both systems are used extensively in the study of materials under high pressure. However, a three-dimensional system capable of substantially higher pressure with the capability of full sample recovery would add a new dimension to the analysis of materials exposed to ultra-high shock pressure. In this thesis, an explosive-based spherical shock-recovery system was designed, tested, and used to perform a series of three-dimensional shock-recovery experiments. A system was desired that would generate extremely high pressure in the sample while maintaining its structural integrity for post-shock analysis. The system consisted of a spherical metallic shell containing a sample of precursor materials at its center. The metallic shell was surrounded by a spherical layer of high explosive. Several detonators were placed at regular intervals around the outside of the explosive layer. To hold the detonators in place during assembly and transport, a spherical brass shell was placed around the explosive. The detonators were placed in holes drilled in the brass shell at the proper locations. To provide confinement for the explosive, this assembly was placed inside a short section of naval gun barrel. The remaining volume of the barrel was filled with sand to aid confinement. Several shock-recovery experiments were performed with the spherical system. Five experiments were performed with samples containing mixtures of nanograde nickel powder and buckeyballs. Two experiments were performed on solid spheres of steel with pearlitic (one inch diameter) and martensitic (1.5 inch diameter) microstructures. The post-shock analysis of the samples consisting of a metallic shell surrounding precursor materials revealed that it is possible to use this system to synthesize materials that under normal conditions are difficult to make. The analysis of the solid spheres revealed that, due to shock loading, a hole was formed at the center of each sphere. In the pearlitic steel sphere numerous changes were made to the microstructure, some of which have not been previously observed. The martensitic sample did not undergo as drastic a change as the pearlitic sample, which by itself is an interesting observation that deserves more study. According to two-dimensional computer simulations performed with the CTH hydocode, this shock-recovery system is capable of producing ultrahigh pressure levels in both solid and powder materials. The simulations indicate that the pressure in the one inch diameter sphere increases from 50 GPa at the surface of the sphere to about 1 TPa at its center, 0.5 inches away.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Doctoral

Grantor dc:publisher

Texas Tech University

Year dc:date.issued

2001

Author dc:creator

• Wilson, James N

• Shock (Mechanics)
• Materials at high pressures

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/2346/20035

OAI identifier oai:identifier

oai:ttu-ir.tdl.org:2346/20035