Abstract
Jerky flow has recently aroused interest as an example of complex spatiotemporal dynamics resulting from the collective behavior of defects in Al- and Mg-based alloys under loading. This paper presents the results of the study of the macroscopic strain localization kinetics in Nickel 200 (99.5 wt % purity). Uniaxial tension of flat samples is monitored at room temperature in the load–unload mode at a constant strain rate and total deformation increment up to 5%. The stress–strain curves reveal jerky flow from the yield point to the formation of the neck. The digital speckle correlation method evidences the movement of localized plastic deformation bands under the conditions of the Portevin–Le Chatelier effect (PLC). It is shown that stress drops during jerky flow in Ni are accompanied by the formation of morphologically simple single PLC bands. It is established that, with an increase in total deformation, the number of PLC bands and their velocity of motion along the sample decrease, while their time period increases. Moreover, an increase in total deformation leads to an increase in the parameters of the force response (i.e., time period and stress drop magnitude). It is found that the criterion of damage for PLC bands as a function of the total strain has a sigmoidal shape.
Highlights
Applying mechanical loads induces various phenomena in crystalline solids
The dynamics and morphology of strain localization at the macroscale level are usually studied in terms of the Lüders phenomena, serrated flow and Portevin–Le Chatelier (PLC) effects, as well as the neck formation at failure, which occur during active deformation of the material [7,8,9,10,11,12,13,14,15]
The difference between the velocity of the PLC bands in the load–unload mode and the velocity of motion of the mobile gripper is found to be ~101–103 times
Summary
Applying mechanical loads induces various phenomena in crystalline solids. Among them, special attention is paid to plastic deformation that may occur far from thermodynamic equilibrium in self-organized structures with decreasing entropy. Classical examples when the instability of an initially homogeneous nonequilibrium and nonlinear medium causes the evolution of complex forms of the separation front are diffusion flame fronts, diffusion aggregation of particles, chemical reaction and shock ionization in porous media, bacterial population growth and so on [3,4,5,6]. Another example of nonequilibrium morphogenesis is the spontaneous formation of complex spatiotemporal structures of macroscopically localized plastic deformation in a deformable solid under loading conditions. The dynamics and morphology of strain localization at the macroscale level are usually studied in terms of the Lüders phenomena, serrated flow and Portevin–Le Chatelier (PLC) effects, as well as the neck formation at failure, which occur during active deformation of the material [7,8,9,10,11,12,13,14,15]
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