Most solid materials undergo plastic deformations when subjected to strong shocks.  The point on the shock Hugoniot at which a material transitions from a purely elastic state to an elastic-plastic state is called the Hugoniot elastic limit (HEL) and the pressure at which this transition takes place is denoted p.  Values of p can range from 0.2 GPa to 20 GPa.  Above the HEL, the material loses much of its shear strength and starts behaving like a fluid.