A study of localisation in dual-phase high-strength steels under dynamic loading using digital image correlation and FE analysis

TL;DR

This study investigates strain localization in dual-phase high-strength steel under dynamic loading using digital image correlation and finite element analysis, revealing early localization and validating models with experiments.

Contribution

It introduces a novel specimen design for high-rate testing and combines digital image correlation with FE analysis to study strain localization in dual-phase steel.

Findings

Strain localization begins before maximum load at high strain rates.

Good agreement between experimental and numerical stress-strain responses.

Mesh density influences deformation localization in simulations.

Abstract

Tensile tests were conducted on dual-phase high-strength steel in a Split-Hopkinson Tension Bar at a strain-rate in the range of 150-600/s and in a servo-hydraulic testing machine at a strain-rate between 10-3 and 100/s. A novel specimen design was utilized for the Hopkinson bar tests of this sheet material. Digital image correlation was used together with high-speed photography to study strain localisation in the tensile specimens at high rates of strain. By using digital image correlation, it is possible to obtain in-plane displacement and strain fields during non-uniform deformation of the gauge section, and accordingly the strains associated with diffuse and localised necking may be determined. The full-field measurements in high strain-rate tests reveal that strain localisation started even before the maximum load was attained in the specimen. An elasto-viscoplastic constitutive model is used to predict the observed stress-strain behaviour and strain localisation for the dual-phase steel. Numerical simulations of dynamic tensile tests were performed using the non-linear explicit FE code LS-DYNA. Simulations were done with shell (plane stress) and brick elements. Good correlation between experiments and numerical predictions was achieved, in terms of engineering stress-strain behaviour, deformed geometry and strain fields. However, mesh density plays a role in the localisation of deformation in numerical simulations, particularly for the shell element analysis.