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An interesting characteristic of virtually all materials is their strain-rate sensitivity. In the case of engineering thermoplastics, these materials exhibit ductility and very good impact resistance at low to average strain rates (<10 %/sec) but can become extremely brittle and unforgiving at high strain rates (100 - 5.000++%/sec). This becomes a concern in energy management applications, such as automotive instrument panels and knee bolsters, because, for example, the average head impact on an instrument panel induces a 1,000%/sec strain rate. Engineering analysis of the impact event typically under-predicts loads and over-predicts deflections. Making material substitutions within a design may be of little use since the newcandidate may be more strain-rate sensitive than the original polymer. Many of the most widely specified engineering thermoplastics behave very differently in standardized ASTM “static” tests than in high strain-rate situations.