Direct impact Hopkinson compression bar experiment for testing at a strain rate of 50,000 s-1

Abstract

A direct impact Hopkinson compression bar experiment is used for compression testing at strain rates in the order of 50,000 s^-1. A short specimen mounted on the end surface of a short transmitter bar is impacted directly by a projectile (the incident bar in the classical split Hopkinson bar is eliminated). The quantities measured in the test are the projectile impact velocity, the force in the transmitter bar and the strain on the surface of the specimen, which is measured using the digital image correlation method with a high-speed camera. The deformation measurements show nonuniform deformation in the specimen. To study the strain rate sensitivity of the specimen material, the experiment is simulated using an assumed material model which is validated by comparing the calculated and measured experimental quantities. Results from tests on aluminum 2024-T351 show a small increase in strain rate sensitivity (increase of stress with strain rate) at strain rates above 10,000 s^-1.