Spherical Acrylic Plastic Hulls Under External Explosive Loading

Abstract

NEMO-type acrylic spherical hulls have been subjected to underwater explosions in order to determine their resistance to hydrodynamic impulse loading. Six 15-in. OD and one 66-in. OD spheres have been subjected to explosions of sufficient magnitude to initiate fracture in the hull. The tests were conducted at simulated depths of 10, 100, 1000, and 2000 ft utilizing explosive charges of 1.1, 8.2, 14.6, 169.9, 387.8, and 688.6 grams. The tests have shown that an acrylic sphere will fracture in 0–50 ft depths range under dynamic peak pressures that are smaller in magnitude than static pressures required for general implosion of the sphere. At depth that is equal to 0.2 of static implosion pressure, the magnitude of dynamic peak pressures must be in excess of the static implosion pressure before fracture of the acrylic sphere is initiated. Fractures were generally initiated on the internal surface of the sphere at two locations: (a) at a point closest to the explosive and (b) at a point most remote from the explosive. The fractures were generally in the shape of a star.