Identification of Constitutive Model Parameters in Hopkinson Bar Tests

Abstract

In this work, tension and compression tests have been carried out on aluminium samples at low and high strain rate, the latter performed by means of a direct tension Hopkinson bar equipment. The parameters of the Johnson-Cook constitutive model have been identified using different approaches; the first method consists in the classical Finite Element Model Updating, where numerical simulations are repeated with different material parameters until the mismatch between the experimental and numerical load–displacement curves falls below an acceptable threshold. The second method is based on the analysis of the digital images acquired by a fast camera during the tests; this permitted to calibrate the JC model by an analytical minimization procedure, without any FE simulation. A third inverse technique was also implemented, consisting in applying the FE model updating but using an enriched cost function, where also the mismatch between the numerical and acquired specimen shape profiles is included and minimized. The advantages and drawbacks of the different techniques are assessed and compared

Evolution of specimen strain rate in split Hopkinson bar test

“…For the M & S-based design/understanding of the high-strain-rate behaviour of solids and structures, a strain rate-dependent constitutive model 8–11 is indispensable (together with the fracture model and equation of state, if necessary). A number of uniaxial stress–strain curves measured precisely at a wide range of strain rates 12–23 are required for the calibration of the strain rate-dependent constitutive model.…”

“…The fundamental theory and applications of SHB are well described in the literature (books 26–29 and review papers 30–34 ). The SHB is used to determine the dynamic stress–strain curves of not only metals 12–23 but also non-metallic materials 35–45 such as ceramics, concrete, rocks, soil (sand), plastics, rubber, foam, honeycombs, wood, and various types of composites.…”