This paper presents an experimental investigation into the dynamic response of three free floating stiffened metal boxes with protective coatings subjected to underwater explosion (UNDEX). One box was kept intact while the other two were, respectively, covered with monolithic coatings and chiral honeycomb coatings. Three groups of live fire tests with different attack angles and stand-off distances were conducted. The acceleration on the stiffener and strain peak on the bottom hull were selected as the major comparative criterions. Test results show that the impulse transmitted to the structure at the initial stage can be reduced, owing to the coating flexibility and fluid-structure interaction mechanism. Consequently, the acceleration peaks induced by both shock wave and bubble pulse were reduced. The shock environment can be more effectively improved by honeycomb coating when compared with monolithic coating. Most of the strain peaks decreased to a certain extent, but some of them were notably manifested, especially for honeycomb coating. The test affirms the fact that soft coating can cause stress concentration on the shell that is in direct contact with the coating due to the impedance mismatch between the interfaces of materials. A softer rubber coating induces a greater magnitude of strain. 1. Introduction In naval warfare, warship and submarine will inevitably suffer from underwater explosions. Unlike contact explosion, noncontact explosion does not break ship’s hull, but shock wave and bubble pulse usually cause great impact to ship and result in the permanent deformation of hull plate, breakdown of onboard equipment and casualty of personnel. How to moderate the devastating damage is very important and of great interest to ship designers. Many efforts have been taken to enhance the warship’s blast resistance since World War I (WWI). Early measures include reinforcing the hull and building the multilayer hull, but very complex engineering constructions are needed and big volumes are occupied. Such inconvenience prevents a further use of these techniques in modern ships [1]. Furthermore, existing devices and units mounted on the ship cannot meet the needs of good shock and vibration isolation at the same time [2]. Moreover, these units cannot reduce the total shock wave energy transmitted to ship. In 1990s, US navy [3] studied the shock resistance of a ship covered with protective coating. Research at the Naval Postgraduate School continues in an effort to understand the dynamic response of coated structures subjected to shock waves. The coating
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