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A previous paper detailed the generation of high strain-rate data (greater than 100%/sec) on engineering thermoplastic materials. These data were used in conjunction with dynamic finite-element analysis techniques to predict the load-deflection response of instrument panel retainers that were impacted with an approximate head form. Correlation between analysis results and physical testing for part stiffness, strength, and ductility were very good for a variety of materials. Use of such data represents a vast improvement in analysis accuracy versus the use of traditional material data in these types of analyses. Methodology for the use of high strain-rate data is explained and demonstrated through this correlation. The technique can be used to evaluate and improve future instrument panel designs. Also, suggestions for further development work in the area of materials models are made.

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.