An experimental evaluation of residual properties in explosively formed stainless steel tubes

Includes bibliographical references (pages 51-52)Cold drawn type 316 stainless steel round tubes, and drawn tubes which were subsequently explosively formed into a hexagonal shape were tested by three experimental stress analysis techniques: deflection, strain gage, and local strain. The purpose of the tests was twofold:(1) to determine the residual stresses resulting from explosive forming, and (2) to compare the three experimental stress analysis techniques. In addition, the tensile and fatigue strength, ductility, hardness, and stress corrosion susceptibility of the as-drawn and the explosive formed stainless steel tube materials were correlated to determine the effect of explosive forming on these properties. Explosive forming was found to completely change prior residual stress patterns. The deflection and strain gage techniques of experimental stress analysis both indicated relatively low residual stress levels in the tubes, i.e., less 15 percent of ultimate strength. The local strain technique gave similar results but the operator induced data scatter w ere much greater. The mechanical strengths were increased significantly in the explosive formed tubes, as was the susceptibility to stress corrosion. Ductility and hardness both showed significant decreases after explosive forming. In view of the increased strength resulting from explosive forming, the residual stresses in the hexagonal tubes are probably inconsequential as compared to the residual stresses in the as-drawn tubes