Dynamic Fracture in Metals under Biaxial Strain Conditions

An experiment to investigate the influence of biaxial strain on the dynamic fracture of metals is outlined. A hollow cylindrical specimen is loaded on the inner diameter by a polyethylene coated exploding wire which results in a circumferential spallation pattern. Prior to fracture, the spall plane undergoes biaxial deformation with a total hoop strain of the same order of magnitude as the total radial strain. The role of plastic pre-straining on the fracture threshold is shown to be negligibly small as evidenced by a series of tests where the specimens were statically and dynamically prestrained in the radial, tangential, and axial directions. Kerr cell pictures of the coated exploding wires and dynamic flash X-rays of the specimens are included to demonstrate the axi-symmetry of both the loading and the spall phenomena. (Author)