Some basic aspects of electromagnetic radiation during crack propagation in metals

Measurements of the electromagnetic radiation (EMR) emitted during crack propagation and fracture and the effect of modes of fracture, physical properties and high temperature on the characteristics of emitted EMR from metals have been discussed. It has been observed that all the three modes of fracture give rise to EMR emission; however, the relative amplitude in tearing mode is very low. A linear variation of EMR peak voltage with bond energy has been observed while frequency varies parabolically with bond energy. Both these curves indicate that no EMR emission or negligible EMR emission is expected in metals having bond energy <270 kJ/mole. EMR characteristics decrease with increase in lattice parameter. Higher tensile strength metals emit stronger EMR signals. Experiments conducted at high temperatures validate the prediction of Molotskii that an increase in specimen temperature should decrease the EMR frequency. One additional but important observation has been that while the EMR peak amplitude decreases with increase in temperature in steel, it increases with increase in temperature in copper.