The influence of free water content on ballistic performances of concrete targets

Abstract During the last decades, the study of the influence of free water content on performances of concrete has been improved by numerous experimental works. It is believed that wet concretes exhibit much lower deviatoric strength capacity, higher volumetric stiffness, and more strain-rate sensitivity compared to dry concretes. In this paper, the Kong-Fang concrete model recently proposed (Int J Impact Eng 2018, 120: 60-78) is modified to capture the effect of free water content. Three major modifications are made respectively to the strength surface, dynamic increase factor (DIF), and equation of state of the original model to capture the influence of free water content mentioned above. The modified strength surface, DIF, and equation of state for wet and dry concretes are compared with experimental data and show good agreements. The modified Kong-Fang model is then implemented into the finite element code LS-DYNA through user-defined material model. Single element tests including biaxial compression and triaxial compression are firstly performed to validate the modified model at a material point level, where corresponding predictions are compared with experimental results and good agreements are obtained. The influence of free water content on ballistic performances of concrete is then systematically investigated with the modified model. The predicted time-histories of projectile velocity, deceleration, and penetration depth are well consistent with the experimental data. It is found that the wet concrete exhibits higher penetration resistance compared to a dry concrete reflected in a lower projectile residual velocity for perforation case and smaller penetration depth for penetration case.