Acoustic emission (AE) generated during simple upsetting (forging) of solid cylinders contains information that could potentially be used to separate the upsetting process into a range of zones of plastic deformation and a zone of both plastic deformation and cracking. This investigation monitored the AE signals during the upsetting of cylindrical specimens of 7075-T6 Aluminum from the start of plastic deformation through eventual cracking. The count rate (N˙) and cumulative count (N) as a function of effective strain were determined. The count rate data are characterized by three distinct regions, an initial peak during yielding of the material, a period of gradual increase during the progression of plastic deformation and the accompanying changes in specimen geometry, and finally a region of rapid increase in N˙ as cracking begins. The cumulative count and rms data follow similar patterns. An analysis of the amplitude distribution of the cumulative count data over a range of strain was made, and in the region of higher amplitude emissions, changes in the distribution of up to two orders of magnitude are observed for data obtained during plastic deformation and surface cracking compared to that from the region of pure deformation only. If plotted as log count (N) versus signal amplitude, the resulting data can be fit with a line using least squares methods yielding a power law relationship sensitive to the degree of deformation.
Acoustic emission method in the delayed fracture mechanics of structural materials