Impact-Induced Tensile Waves in a Rubberlike Material

Abstract

This paper concerns the propagation of impact-generated tensile waves in a one-dimensional bar made of a rubberlike material. Because the stress-strain curve changes from concave to convex as the strain increases, the governing quasi-linear system of partial differential equations, though hyperbolic, fails to be "genuinely nonlinear" so that the standard form of the boundary-initial value problem corresponding to impact is not well-posed at all levels of loading. When the problem fails to be well-posed, it does so by exhibiting a massive loss of uniqueness, even though an entropy-like dissipation inequality is in force. Because the breakdown in uniqueness is reminiscent of a similar phenomenon that occurs in continuum-mechanical models for impact-induced phase transitions, a mathematically suitable, though physically unmotivated, supplementary selection mechanism fordetermining the solution naturally suggests itself. We describe in detail the solutions determined by two special forms of this selection mechanism, and we show that these two solutions provide bounds on the impact response, regardless of the selection principle used.