Crack tip behavior under pulsed electro-magnetic loading

Summary form only given, as follows. Examines the behavior of cracked bodies due to pulsed electro-magnetic loading. There are two main aspects of EM loading: a) the EM field creates a concentrated body force field near the crack tip; b) it also creates a concentrated heating due to concentration of current density near the crack tip. Since the material strength is lowered at elevated temperature, a nominal ductile behavior is expected near the tip. If the heating is severe, melting may also be expected. The amount of heating depends on electrical resistivity, thermal conductivity and heat capacity of the material. Thus the net effect could be either brittle or ductile behavior depending on the interplay of various thermal, mechanical and electrical properties. It is possible that in some conductors the pulse loading will cause crack extension and in others crack arrest due to tip melting and blunting. Experiments were conducted on aluminum plates on which two cracks were symmetrically pre-cut at the center. A test fixture was designed to the cracked plate between two copper bars connected to the power supply. After each pulse the sample was unmounted and examined under an optical microscope. The peak current was varied to examine the effect of peak current level on the crack tip behavior. It was found that the crack tip linearly extended, got blunted by cavitation (formation of blow hole due to high heating) or bifurcated depending on the level of the peak current. Multiple pulses were also applied on one sample to study the effect of repeated pulsing on crack extension. Finite element computations were performed using the electro-magnetic code EMAP3D code in conjunction with the stress code DYNA3D code. The computational results confirm most of the features observed in the experiments.