Studying the Heterogeneity of Plastic Deformation at the Stage of Prefracture of a Copper–Nickel Alloy

Plastic deformation tends to localize at all stages, from the beginning to the end (until fracture), taking on various regularly changing forms along the way. Localization of plastic flow can cause failure of materials during technological processes associated with large plastic deformations. In this regard, it is necessary to establish the laws governing plastic deformation localization throughout the entire length of the stress–strain curve, from the yield strength to the ultimate strength. Knowing the regularities of localization of a plastic flow, one will be able to formulate a criterion for predicting the ductility reserve of materials. Speckle photography has shown promise for studying the features of plastic deformation of metals. The spatial resolution of this method corresponds to the optical microscopy level with a significant advantage in the size of the field of view. This method allows one to obtain the values of components of the plastic distortion tensor of the working surface of a sample with an interval of 30 s (the maximum displacements of surface points are 100 μm) and, ultimately, analyze the evolution of localization patterns and determine the kinetic parameters of moving localization foci. In this study, speckle photography has been used to examine the kinetics of development of localized plastic deformation foci in the polycrystalline MNMts40-1.5 copper–nickel alloy. It has been found that the forms of localization are completely determined by the laws of strain hardening of a material acting at a certain process stage. The localization of a plastic flow in the copper–nickel alloy has an autowave character. In this case, on the yield plateau, the localization patterns observed at the linear and parabolic strain hardening stages and the prefracture stage reflect different types of the autowave processes. By analyzing the characteristics of these processes, their propagation velocity and wavelength have been measured. A method for identifying the source of destruction for predicting the ductility reserve of metals has been proposed.