Effect of notch-depth ratio on intermittent electromagnetic radiation from Cu-Ni alloy under tension

Abstract

This paper presents some experimental results on the effect of the notch–depth ratio on intermittent electromagnetic radiation during the progressive plastic deformation of a Cu-Ni alloy sheet specimen under tension. An electromagnetic antenna was used for receiving the electromagnetic waves emitted by the deforming specimen. The specimens (with varied notch-depth ratios) first emit electromagnetic radiation near yield which is always oscillatory in nature. However, the axial strain at the initial emission of the electromagnetic radiation increases with an increase in the notch-depth ratio. The nature of electromagnetic radiation signals changes from oscillatory to exponential until instability is reached. This shows that the viscous coefficient of the material of the specimens increases during strain-hardening. The paper also presents a correlation between electromagnetic radiation emission parameters and the radius of the plastic zone created ahead of the advancing crack tip, an important parameter in fracture mechanics. With an increase in the plastic zone size, the amount of intermittent electromagnetic radiation decreases asymptotically: the first electromagnetic radiation amplitude increases linearly and a maximum energy burst first decreases the electromagnetic radiation frequency parabolically. Initial electromagnetic radiation characteristics differ considerably from optimum electromagnetic radiation emissions within the strain-hardening region. These experimental results show a novel technique for studying various fracture mechanics parameters and also for developing a non-contact crack growth monitor.