INVERSE COMPUTATIONAL DETERMINATION OF JOHNSON-COOK PARAMETERS USING THE SHPB TEST APPARATUS

Anja Mauko,Branko Nečemer,Zoran Ren

doi:10.14311/app.2019.25.0064

Abstract

The paper describes determination of the material parameters of the Johnson-Cook constitutive model of steel S235 JR sample material by applying the inverse computational methodology using the digital twin model of the SHPB. A quasi-static tensile testing of bulk material was conducted ﬁrst to determine the base material parameters. This was followed by dynamic impact testing at two diﬀerent strain rates using the SHPB. A digital twin computational model was built next in the LS-Dyna explicit ﬁnite element system to carry out the necessary computer simulations of the SHPB test. The inverse determination of strain hardening material parameter of Johnson-Cook model was done by using the Nelder-Mead simplex optimisation by comparing the measured and computed stress to time signals on incident and transmission bars. The obtained Johnson-Cook material parameters much better describe the sample material behaviour at very high strain-rates in computational simulations, if compared to the parameters derived by the classic, one-dimensional wave propagation Hopkinson procedure.

Highlights

Many studies have been carried out in the past to understand and enable predicting the material response under dynamic impact loading
A digital twin computational model was built in the LS-Dyna explicit finite element system to carry out the necessary computer simulations of the Split Hopkinson Pressure Bar (SHPB) test
The obtained Johnson-Cook material parameters much better describe the sample material behaviour at very high strain-rates in computational simulations, if compared to the parameters derived by the classic, one-dimensional wave propagation Hopkinson procedure

Summary

Introduction

Many studies have been carried out in the past to understand and enable predicting the material response under dynamic impact loading. The JohnsonCook (JC) constitutive model is most commonly used to describe the material strain-rate dependency in dynamic computer simulations. This paper describes an inverse computational method used to determine the strain-rate dependent parameters of the JC constitutive model for steel S235 JR [1]. The base quasi-static constitutive parameters were determined by classic quasi-static tensile testing. The strain-rate dependent material behaviour at different deformation rates was determined by using the Split Hopkinson Pressure Bar (SHPB) test apparatus [2]. The JC model was validated by digital twin simulations of the SHPB

Methods

Results

Conclusion