High rate tensile tests - Measuring equipment and evaluation

Polymers are widely used in protection systems, e.g. in cars. For dimensioning those parts, crash simulation is performed. However, crash simulation programs require reliable high rate mechanical properties to provide accurate results. As polymers are viscoelastic materials Young's modulus and yield stress are rate dependent quantities. In order to determine these properties, special experimental devices and special evaluation methods have to be used. In this paper, the modification of the clamps of a servo-hydraulic tensile testing machine to reach a global strain rate of 670/s is described. Furthermore, a new evaluation method is shown to determine Young's modulus and yield stress using a curve fitting procedure. The results show that both Young's modulus and yield stress depend logarithmically on the strain rate. It is also shown that the rate dependency of the Young's modulus can be used to get rid of the stress oscillations superimposed on the stress signal.