Ultrasonic test for high rate material property imaging

In order to perform experimental identification of high strain rate material models, engineers only have a very limited toolbox based on test procedures developed decades ago. The best example is the so-called Split Hopkinson Pressure Bar (SHPB) which has proved extremely useful but has important intrinsic limitations due to the stringent assumptions required to process the test data. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. One can then use this full-field information in conjunction with efficient numerical inverse identification tools such as the Virtual Fields Method (VFM) identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate loading.This paper presents results a new inertial ultrasonic test to obtain stress-strain curves at high strain rates (here, up to 300/s). The idea is to excite a flat rectangular specimen at its first longitudinal resonance frequency. Images are recorded with an HPV-1 camera from Shimadzu at 250 kfps. It is shown that meaningful stress-strain curves can be obtained using acceleration as a stress gauge