Protection mechanism of liquid-filled welded square steel container with polyurea elastomer subjected to small-arms bullet

The hydrodynamic ram (HRAM) caused by projectile impact would cause severe local damage to and overall deformation of a liquid-filled container. To prevent serious damage and rapid loss of an internal liquid in a thinwalled liquid-filled container upon high-velocity impact, a method involving spraying polyurea elastomer to enhance the impact protection performance of a container was proposed. A ballistic gun was used to launch small-arms bullet to impact a polyurea-coated liquid-filled square steel tube (PCST), and the macroscopic damage characteristics were obtained. The microscopic damage characteristics of polyurea were observed by scanning electron microscopy, the expansion process of cavity in water was photographed by high-speed photography, and the influence mechanism of polyurea layer on HRAM and container protection was further explained by numerical simulation. Results showed that the deflection deformation of the PCST initially increased and then decreased with increasing polyurea thickness. When the thickness of the polyurea was 4 mm, the maximum deflection deformation decreased to 76.3 % of that in the bare container. Competition was observed between the restraint of the polyurea layer and the influence of projectile deceleration on the HRAM, and the protective effect was weakened when the polyurea layer was thin. The polyurea dominated the overall constraint of the structure, and the enhancement of the HRAM aggravated tearing damage at the weak corner-welded joint. When the protective effect was enhanced, the protective ability of the polyurea layer to enhance the liquid-filled container was manifested in two aspects. First, the "self-healing" of polyurea blocked the bullet hole on the steel plate and prevented internal liquid leakage. Second, the energy absorption and deceleration of polyurea weakened the water, thereby reducing damage to the container.