A theoretical model for the electromagnetic radiation emission during plastic deformation and crack propagation in metallic materials

This paper presents a theoretical model for the electromagnetic radiation (EMR) emissions during plastic deformation and crack propagation in metallic materials. It is shown that under an externally applied stress, edge dislocations within the plastic zone ahead of a crack tip form accelerated electric line dipoles which give rise to the EMR emissions. The dynamic motion of these dislocations becomes overdamped, underdamped or critically damped, depending upon the material/microstructural properties such as mass per unit length of dislocation, line tension, damping coefficient, and distance between the dislocation pinning points. The nature of the EMR signals, viz. exponential decay or damped sinusoidal, is decided essentially by these damping characteristics. The EMR emissions are followed by crack propagation inmetallic materials. The EMR has a continuous frequency spectrum with a frequency bandwidth ranging from 108 to 1012 radians s−1, depending upon the properties of the metals. Screw dislocations do not contribute to the EMRemissions. The paper also presents some experimental results on the EMR emissions in ASTM B265 grade 2 titanium sheets. The nature (damped sinusoidal and exponential decay), amplitude and frequency of the observed EMR emissions are in conformity with the predictions of the theoretical model