RUPTURE OF THIN DUCTILE TUBES BY OBLIQUE IMPACT OF BLUNT MISSILES - EXPERIMENTS

Impact tests at both normal and oblique angles of incidence were condu cted on thin mild steel tubes using a moderate size of blunt missile ( D-m/h = 4.33) at various angles of obliquity (0 degrees less than or e qual to phi(0) less than or equal to 60 degrees) from normal. The mini mum impact speed that generated cracks through the thickness of the wa ll, termed the speed for rupture, was measured, and various types of r upture were identified. For a thin tube hit by a flat-nosed missile at a large angle of obliquity, the flat-nose initially cuts into the sur face of the tube wall; through thickness rupture is due to tensile tea ring that occurs in a region just below the crater. The speed for rupt ure of the tube is found to be a minimum at an angle of incidence equa l to 45 degrees; this speed is about 41% less than that required to ru pture a tube of equal thickness by impact at a normal angle of obliqui ty. Ii the missile nose has a radius of curvature of the same order as the missile radius, the deformation is more diffuse in the region imm ediately adjacent to the contact surface; consequently the mode of fai lure changes From predominately shear at the edge of the missile to mo re uniform stretching under the contact surface. For oblique impact of missile with more rounded noses, this causes the observed speed for r upture to increase with increasing angle of obliquity. (C) 1998 Elsevi er Science Ltd. All rights reserved.