Switching Autowaves in Materials with Dislocations and Martensitic Transformations
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SWITCHING AUTOWAVES IN MATERIALS WITH DISLOCATIONS AND MARTENSITIC TRANSFORMATIONS V. I. Danilov, V. V. Gorbatenko, and L. V. Danilova
UDC 539.213:669.017
The paper focuses on the investigation of the strain kinetics at the yield point of materials with shear dislocations and martensitic transformations at a microlevel. In both cases, the autowave propagation and localized plastic deformation occur. The autowave propagation velocity depends on the nonlinear speed of the crosshead movement. It is found that its nature is the same both in low carbon mild steel and titanium nickelide. Keywords: Chernov–Lüders band, martensitic transformation band, localized plastic strain autowaves, nonlinear velocity dependence.
INTRODUCTION The concept of deformation of solids as a multilevel self-organized process naturally has led to the development of the autowave plasticity theory [1]. This theory considers deformation as the evolution of the autowave modes of localized plasticity. Autowave deformations as space-time periodic structures are well-studied at the microand meso-levels. In works [2–6], the evolution of dislocation substructures from chaotically distributed localized dislocations to cellular and striple structures, is described for the macro-level, while the formation of self-organized structures at the meso-level is presented in works [7–9]. Although these levels are not called autowaves, all these works consider the patterns of localized plasticity in solids at the respective scale levels. Zuev and Danilov [10] were first who used the term autowave for the description of localized plastic deformation of solids at the macro-level. That research, allowed identifying the autowave modes during plastic deformation, and an unambiguous relationship matching the correspondence rule [1] between the strain-hardening stages and the respective modes, as presented in Table 1. The greatest attention in subsequent research was paid to phase autowaves of localized plastic deformation. To date, experimental dependencies were obtained for the autowave propagation velocity and the strain-hardening coefficient [11], the autowave length and the parameters of the metal microstructure and the specimen geometry [12]. Based on these data, the law of the autowave dispersion was established and the nature of the entropy change [13] during plastic deformation was analyzed. Also, the introduced elastoplastic invariant reflected the relation between the lattice and autowave parameters of the material [14]. It is, however, unreasonably to limit research into the autowave nature of deformation to phase autowaves, which occur at the stages of linear strain-hardening. On the stress-strain curves, these stages are observed rather rarely and are typical for the materials with a certain type of the dislocation substructure evolution [4] under sufficiently narrow temperature and speed loading conditions. Therefore, it is still not possible to study the influence of temperature and speed of the crosshead movement on the autowave parameters and kinetic
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