Ramirez, N., Figueroa, U., Guevara-Morales, A., and Rojo, A., "High-speed impact tensile tests on polypropylene based materials," SAE Technical Paper 2017-01-5004, 2017.
Simulations of impact events in the automotive industry are now common practice. Vehicle crashworthiness simulations on plastic components cover a wide range of strain rates from 0.01 to 500 s-1. Because plastics mechanical properties are very dependent on strain rate, developing experimental methods for generating stress-strain curves at this strain rate range is of great technological importance. An impact pendulum was modified so that the impact-deformation-fracture process of a specimen hit by the swing of a pendulum could be monitored. Forces were measured with a piezoresistive sensor while deformation was recorded with a high-speed video camera. Engineering stress-strain curves were obtained. Strain rates between 90 to 175 s-1 were achieved. Two polypropylene based polymers were tested at 20°C and -20°C. Curves of both materials and temperatures showed common features such as a maximum peak, a post-yield softening behavior, some strain hardening effects, and a second stress peak followed by fracture.