Analysis of Dynamic Stress Concentration and Strain Rate Concentration for Notched Specimens Used for High Speed Tensile Test

Engineering plastics provide superior performance to ordinary plastics for a wide range of the use. For polymer materials, dynamic stress and strain rate are major factors to be considered when the strength is evaluated. Recently, high speed tensile test is recognized as a standard testing method to confirm the strength under dynamic loads, and it is analyzed by the finite element method; then, the maximum dynamic stress and strain rate are discussed with varying both the tensile speed and the maximum forced displacement. The strain rate concentration factor is found to be constant independent of the tensile speed, which is defined as the maximum strain rate appears at the notch root over the average nominal strain rate at the minimum section. The maximum strain rate is controlled by the tensile speed alone independent of the magnitude of the forced displacement. It is found that the difference between static and dynamic maximum stress concentrations (σmax -σst ) at the notch root is proportional to the tensile speed when u/t≦5000mm/s.