Statistics of energy dissipation in the hypervelocity impact shock failure transition

In the hypervelocity impact event, shock waves subject material to failure transitions with the attendant dissipation of the imparted energy. Under shock compression, failure and dissipation entail intense compression, inelastic shear and compaction. Through shock interactions, states of dynamic tension are achieved and further failure dissipation involves fracture and fragmentation. The nature of failure of solids in the shock environment has encouraged considerable experimental effort through the past several decades. Such efforts have yielded results that suggest universality in the shock failure response over significant spans of shock intensity. Examples include the fourth-power relation between pressure and strain rate in solid-material compressive shock waves, and power-law relations capturing spall fracture strength and fragmentation size scale in dynamic tensile failure. Comparable power-laws also describe the shock compaction of distended solids. The present paper explores a statistical perspective of the underlying micro failure dynamics for the purpose of achieving better understanding of the macro failure trends noted above. A statistical correlation function description of the random micro velocity field is introduced. Through the attendant kinetic dissipation, the statistical fluctuation-dissipation principle is applied to the shock failure transition. From this statistical approach, power-law relations for compressive and tensile shock failure emerge that replicate the reported experimental behaviors.

Thermal Properties of Various Ti-Al-C Composites Prepared by Hot Shock Compaction Utilizing Combustion Synthesis/ Właściwości Termiczne Kompozytów Ti-Al-C Uzyskanych Z Wykorzystaniem Metody Udarowego Zagęszczania Na Gorąco

Hot shock compaction method was utilized for the consolidation of MAX phase composites consisting of Ti, Al and C. This paper presents the production of dense, crack-free composites by combining the combustion synthesis with explosive detonation. Another objective is to investigate various properties of the obtained shock-compacts. The shock compacted materials were post-annealed at 1173 K for releasing the shock-induced strain. As a result, these compacts had strong interparticle bonding strength and few macro cracks. Intermetallic compounds (TiAl, Ti2Al and Ti3Al) and non-oxide ceramics (TiC and Ti4Al2C2) were detected in as-synthesized and annealed materials by X-ray diffraction experiments. Also, lamella structures of Ti4Al2C2 phase were observed by SEM. It was known that the coefficient of thermal expansion increased with increasing temperature, and decreased with increasing TiC content.