An experimental study on the resistance of a polyurea-sprayed structure to low-speed drop hammer impact

Polyurea elastomer, as a new type of protective material, is widely used in the field of military protection due to its excellent mechanical and physicochemical properties. Currently, most of the study on the protective properties of polyurea has concentrated on high-speed impacts, such as explosions and penetration, but there have been fewer studies on low-speed impacts. The purpose of this paper was to systematically study the impact resistance and protection mechanism of polyurea-sprayed composite structures through material mechanical tests and low-speed drop hammer impact tests. The test results showed that with the increase in the strain rate, mechanical properties such as the elastic modulus and tangent modulus of the polyurea material were greatly enhanced. Furthermore, the material underwent a distinct glassy transition phenomenon under high strain rates. A comprehensive comparison of the structural ultimate specific energy absorption of the three sprayed forms revealed that the front-sprayed and back-sprayed forms did not improve the impact resistance of the structure. On the contrary, they reduced the energy absorption efficiency of the steel plate structure. Back spraying was more advantageous than front spraying due to the tensile deformation and lateral diffusion effect of the polyurea material. Although the front polyurea could provide initial resistance, the formation of a large impedance matching structure will significantly increase the peak stress of the back steel plate, which exacerbated the degree of structural damage. At the same time, different polyurea spraying locations led to differences in the form of the structural forces, which caused the structure to exhibit different failure damage modes. •At high strain rates, polyurea material showed a significant glassy transition.•Low-velocity impact resistance of polyurea composite structures was investigated.•Spraying polyurea would reduce the energy absorption efficiency of the structure.•The position of polyurea coating can lead to differences in structural force forms.•Compared with other sprayed form, the back-sprayed form is more advantaged.