The cratering performance of concrete target under true triaxial confinements

Abstract

It is of great significance to evaluate the cratering performances of concrete target subjected to steel projectile impacting. Different from the method proposed by Forrestal et al. (2003) to record the acceleration signals in steel projectile by single-channel acceleration data recorder, a new testing equipment is established in the present study to record the dynamic triaxial responses of concrete target by six lateral bars. The projectile impacts the target through a hollow square bar (one of six lateral bars), and the true triaxial confinements are applied on the target through six lateral bars which loaded by three servo-controlled cylinders. These three forces, i.e. end resistance, lateral reaming resistance, and lateral traction, acted on the projectile toe during cratering process are discussed respectively by wave signal εy- recorded on the left bar in y-axial, by wave signals εx+, εx-, εz+, and εz- recorded on the lateral bars, and by specially assigned strain gauges demonstrated in Appendix B. Series of experiments of concrete targets under various impact velocities and under various confinements are conducted accordingly. Two stages, e.g. the accelerating cratering stage, and the decelerating cratering and penetration stage, are observed in stress σy- profiles. Similar lateral reaming stages are observed in stress profiles of lateral bars. These stress profiles could be used to evaluate forces applied on projectile toe, and lateral tractions could be ignored. Comparing with the cratering process in the impact direction, there are about 10µs delaying for the lateral reaming process. Depth of crater and pulse duration decrease with increasing confinements, and they exhibit obvious velocity and confinement dependency. Three dimensionless factors, i.e. the inertial effect, the strength effect, and the deformation characteristics, are introduced to evaluate the crater depth. Strength of concrete target is proven to be the most important factor in the cratering process for concrete target under lower impact velocity. This work provides comprehensive and profound understanding of the effects of multiaxial confinement on the crater resistance for concrete-like materials.