Study on the blast-resistance of polyurea-steel plates subjected to underwater explosion

The mitigation of damage to ship hulls due to underwater explosions (UNDEX) has attracted more and more attention. Spraying polyurea on steel plates has been proven to be an effective method. This study investigated the best thickness ratio of polyurea and steel and the ability to absorb energy of polyurea-steel and bare metal by using theoretical analysis. When the Young's modulus of polyurea was in the range of 80 MPa–160 MPa, the best thickness ratio increased from 2.2 to 4.6. Air-backed plate tests were conducted to investigate the influence of spraying thickness and methods of polyurea on the blast resistance, and results were statistically analysed using 3D scanning technology. The final plastic deformation of steel, which had polyurea coated on the front face, was the least out of the three spraying methods. Furthermore, the best protective effect at the smallest areal density was observed when the polyurea sprayed on the front face was three times the thickness of the substrate. This reduced the deformation experimentally and theoretically by 54.5% and 47.4%, respectively. Additionally, the blast resistance of polyurea-steel was not as good as that of bare steel under the same areal density. Finally, a full-scale ship with 8 mm-thickness of bottom steel with a 24 mm-thick polyurea layer was subjected to UNDEX with 33 kg spherical TNT charges. The ability of polyurea to reduce the final plastic deformation of steel is lesser than that in air-backed plate tests. However, the deformation area of the bottom steel with polyurea increased by 40.1% compared to bare metal.