Numerical prediction of dynamic tensile failure in concrete by a corrected strain-rate dependent nonlocal material model

Abstract

Dynamic tensile failure (e.g. spall) is frequently observed when concrete structures are subjected to blast and impact loadings, which is accompanied by the increase of tensile strength with increase of loading rate. Accurate prediction of dynamic tensile failure in concrete material is a challenging problem, in which the strain-rate effect should be properly considered. In the present study, a new corrected strain-rate enhancement model is proposed by introducing a time scale to control the evolution of strain-rate, as to capture the delayed stress response under variations of strain-rate. This corrected strain-rate enhancement model is then combined with the damage-based nonlocal model recently proposed by Kong et al. [18] to investigate the influence of strain-rate effect on numerical predictions of dynamic tensile failure. Numerical examples of a 1D spalling test demonstrate that the introduction of a time scale in the corrected strain-rate captures the delayed stress response and has a weak regularization effect. Three sets of experiments, namely, the Split-Hopkinson Tensile Bar (SHTB) test, the Modified Split-Hopkinson bar (spalling) test and the Compact Tension test, are numerically simulated using the proposed corrected strain-rate enhancement model and the frequently-used instantaneous strain-rate enhancement model. It is found that, considering the instantaneous strain-rate enhancement in the material model, the multiple cracks and crack branching cannot be well predicted, and the capability of energy absorption of concrete structures is overestimated, which may lead to an unsafe design. Promising predictions of dynamic tensile failures in concrete, including multiple cracks, crack branching and the structural resistance are obtained by the damage-based nonlocal model incorporating with the corrected strain-rate enhancement model.