Experimental study of the oblique impact and ricochet characteristics of cylindrical fragments

When the casing charge exploded near or inside a steel installation such as a ship or plant, part of the fragments would impact the target plate and ricochet. Plastic deformation occurs on both the fragment and target plate during the oblique impact, in which the direction and velocity of fragments change. The ricochet of fragments would change the damage range, which cannot be predicted by previous theories. In our experiment, cylindrical fragments were used to impact target plates under different impact velocities and angles, and the target plates are made of marine steel 921A and commonly used Q345B, which are the two most commonly used steels for ships and steel installations. The empirical formulae of ricochet velocity and angle for two target plates were obtained, which were applicable to the positive ricochet. The ricochet velocity increased with the increase in impact velocity and angle, but the ricochet angle only increased with the increase in impact angle. In addition, the ricochet velocity increased with the increase in the hardness of target plate when the impact angle was less than 40° due to the deformation of the target plate, the ricochet angle increased with the increase in the hardness of target plate since the pile-up effect would increase the deflection, causing the ricochet angle decreased. The fragment mass loss model was obtained based on the experimental data, which is a strong function of impact velocity but a weak function of impact angle. With the increase in impact angle, the plastic deformation of fragments gradually decreased, the target plate changed from plastic compression deformation to shear deformation, the deformation energy of target plate changed from volumetric energy to more shear strain energy, and the impact crater became shallower. With the increase in impact velocity, the plastic deformation of fragments increased, the inertial resistance of target plate increased, the impact crater on the target surface became larger and deeper, and then only the depth of impact crater increased when the impact velocity reached a certain extent. The plastic deformation of target plate decreased with the increase in the hardness. The proposed formulae and model can provide guidance for the fragment damage range evaluation and equipment protection.