Critical Conditions for Failure; Stress Levels, Length Scales, Time Scales.

There is a range of thresholds for the response of condensed matter under loading in compression, from the yield point to that at which the bond strength is overcome and warm dense matter is formed. Yield stress shows a correlation between the length scale swept by the rise of the pulse and the defect distribution within the target for a range of materials. Strain rate is also a useful term that reflects the evolution of the stress state within a target but must also be defined for a volume element containing a particular defect distribution to reflect continuum conditions acting within; it thus applies to a defined length scale within a target. Examples are shown using shock pulses that spall metal targets. Different stacking shows differing behaviour yet in each case momentum is conserved. This overview suggests simple observations must take account of mechanisms operating at different timescales and lengthscales in the development of damage in materials and structures. [ABSTRACT FROM AUTHOR]