Planar, longitudinal, compressive waves in solids: Thermodynamics and uniaxial strain restrictions

Abstract

A new tri-axial pressure-based constitutive expression has been found using Cauchy's stress tensor. This stress state emphasizes pressure and shear stress. The description is a pressure plus an effective shear stress allowing for a constitutive law based on atomic solid-state phase changes in crystalline cells due to pressure plus shear-based dislocation motion commonly associated with plasticity. Pressure has a new role in the material's constitutive response as it is separated from plasticity. The thermo-mechanical system describes third-order Gibbs’ expressions without specific volume restrictions placed upon the material. Isothermally, the ratio of heat to shear work in elastic copper is shown to approach zero at a very low temperature and become larger than one as temperature approaches melting. Wave compression models investigated are elastic and plastic: in fully elastic materials, the planar wave is restricted by Poisson's effect although plastic shear changes this constraint. Plastic deformation, dominated by dissipative shear stresses in uniaxial strain, heats the material while excluding phase changes from hydrostatic pressures. The material properties per se across Hugoniot shocks are described with entropy concepts. Shock waves are exceedingly complex since the constitutive laws are linked at extreme temperatures, pressures, and shear stresses. Isothermal, isentropic, isochoric, and iso-shear conditions are used throughout with Jacobian algebra.

Elastic-Plastic Wave Propagation in Phononic Crystals

“…After the initial research focus in the 1940's, the subsequent three decades witnessed the maturation of plastic wave theory, with a focus on exploiting the distinct speeds of elastic and plastic waves using the method of characteristics [16][17][18][19][20][21][22][23]. Over time, this theoretical treatment expanded to encompass rate effects [24][25][26], lateral inertia [27][28][29], anisotropy [30][31][32], thermodynamics [33][34][35][36][37], and microstructural concerns [38][39][40]. Additionally, as analytical solutions to these problems proved elusive, numerical methods, such as Godunov schemes and similar Riemann solvers, were developed to simulate plastic wave propagation [41][42][43][44][45][46][47].…”