Figure 1. Results from our compression tests on each of the target materials at specified quasistatic strain-rates (top) and high strain-rates (bottom). Multiple tests were performed on each target material (I-90 (a), I-94 (b) and I-90 (b)). Engineering values always use as the reference the initial area or length. Engineering stress is the force divided by the initial area, which is a good estimate of the stress for small changes in area. Engineering strain is the increase in length divided by the initial length.