Crack tip behavior under pulsed electromagnetic loading

This paper describes a series of experiments and their numerical simulations in which cracks were created in conductors by using high-transient magnetic fields. The tests were conducted on small samples of 7075 aluminum alloy in a test fixture that placed the samples in series with a high-voltage capacitor bank and constrained the samples from moving. Notches were machined in the samples at various depths for the purpose of creating an initiation site for the cracks. After each pulse, the samples were unmounted and examined under an optical microscope. The peak current was varied to examine its effect on crack tip behavior. It was found that the crack tip extended linearly, was blunted by cavitation (blowholes formed due to intense heating), or bifurcated-depending on the level of the peak current. Multiple pulses were also applied to one sample to study the effects of repeated pulsing on crack extension. Finite-element computations were performed using the three-dimensional finite-element analysis program EMAP3D in conjunction with the stress code DYNA3D. The computational results confirm most of the features observed in the experiments.