Modification of charpy machine for the acquisition of stress-strain curve in thermoplastics

Abstract

Simulations of impact events in the automotive industry are now a common practice. Vehicle crashworthiness simulations on plastic components cover a wide range of strain rates from 0.01-500 s-1. Because plastic 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. In this paper, a modified Charpy machine capable of acquiring useful information to obtain the stress-strain curve is presented. Strain rates between 300-400 s-1 were achieved. Three thermoplastics were tested: high-density polyethylene, polypropylene-copolymer and polypropylene-homopolymer. Impact simulations using LS-DYNA were performed using the acquired high-strain rates stress-strain curves and compared with experimental data. Simulations using stress-strain curves from quasi-static tests were also performed for comparison against high-speed. Very good agreement between the simulation and experimental results was found when the ASTM D1822 type S specimen was used for testing each material.