Wave phenomena in low-rate plastic flow of solids

An investigation of plastic flow localization patterns (waves) which are ordered in space and evolve with time has been performed for a wide range of metals and alloys. These waves are found to have the following basic features: the dependence of propagation rate on work hardening coefficient, dispersion law and scale effect. The possibility of addressing plastic flow localization as a self‐organization process occurring in a deforming medium is considered. A set of equations appropriate for the description of local flow nuclei is discussed. Consideration is given to a change‐over from one local strain pattern to another in accordance with the respective stages of flow. Proposed is a model for interpreting the large‐scale periodicities exhibited by the distribution of localized strain nuclei.

An experimental and theoretical study of plastic shear localization mechanisms observed under dynamic deformation using the shear–compression scheme on a Hopkinson–Kolsky bar has been carried out using specimens of AMg6 alloy. The mechanisms of plastic shear instability are associated with collective effects in the microshear ensemble in spatially localized areas. The lateral surface of the specimens was photographed in the real-time mode using a CEDIP Silver 450M high-speed infrared camera. The temperature distribution obtained at different times allowed us to trace the evolution of the localization of the plastic strain. Based on the equations that describe the effect of nonequilibrium transitions on the mechanisms of structural relaxation and plastic flow, numerical simulation of plastic shear localization has been performed. A numerical experiment relevant to the specimen-loading scheme was carried out using a system of constitutive equations that reflect the part of the structural relaxation mechanisms caused by the collective behavior of microshears with the autowave modes of the evolution of the localized plastic flow. Upon completion of the experiment, the specimens were subjected to microstructure analysis using a New View-5010 optical microscope–interferometer. After the dynamic deformation, the constancy of the Hurst exponent, which reflects the relationship between the behavior of defects and roughness induced by the defects on the surfaces of the specimens is observed in a wider range of spatial scales. These investigations revealed the distinctive features in the localization of the deformation followed by destruction to the script of the adiabatic shear. These features may be caused by the collective multiscale behavior of defects, which leads to a sharp decrease in the stress-relaxation time and, consequently, a localized plastic flow and generation of fracture nuclei in the form of adiabatic shear. Infrared scanning of the localization zone of the plastic strain in situ and the subsequent study of the defect structure corroborated the hypothesis about the decisive role of non-equilibrium transitions in defect ensembles during the evolution of a localized plastic flow.

Plastic flow localization in h.c.p. Zr alloys on macro- and microscale levels

A new model of localized plastic flow and failure of solids

Nonlinear interaction of geometrical and material properties in sandwich beam instabilities

Ductility limit prediction using a GTN damage model coupled with localization bifurcation analysis

The fundamental mechanisms of strengthening/hardening and toughening that may be modified by various nanometer-spaced planar defects in the ultrahard nanostructured diamond and boron nitride (BN), e.g., nanotwins, stacking faults, and coherent heterophase interfaces, are still far from understood. In the present work, by means of first-principles approaches to derive ideal strength and Peierls stress, we performed a comprehensive investigation on the effect of the nanometer-spaced planar defects on the strength and plasticity of nanostructured diamond and BN under both uniform and localized deformations. A profound strengthening under uniform strain is revealed to be closely dependent on the spacing of planar defects, yet differing from the disappearing dependence under localized strain. It is further shown that the breakage and reconstruction of covalent bonds occurs only for very small spacing of planar defects under uniform deformations, being inconsistent with the average spacing found in the experimentally prepared nanotwinned diamond and BN, thus casting a doubt on the feasibility of the previously proposed strengthening mechanism. Under localized deformations, only the planar defects of twin in c-diamond or c-BN and coherent heterophase interface in c-/h-diamond or c-/w-BN are found to increase the barrier for the parallel slip of both $1/2\ensuremath{\langle}110\ensuremath{\rangle}$ shuffle-set full dislocation and $1/6\ensuremath{\langle}112\ensuremath{\rangle}$ glide-set partial dislocation, resulting in the strengthening of nanostructured diamond and BN, which agrees to the experimental observation. These findings not only yield a physical insight in strengthening/toughening nanostructured diamond and BN, but highlight the importance to understand the synergetic effect of length scale and interface between planar defects in designing superhard nanostructured materials.

Microstructure evolution in pearlitic steels during wire drawing

The instability of plastic flow at low temperatures appears to be quite a general phenomenon of many metallic materials. Several theories have been advanced to account for this effect: strain-induced phase transformations1 and twins,2 avalanche-like barrier crossing by dislocation pile-ups and their sudden multiplication under the action of the load,3 and thermal instability of deformation resulting from a large temperature dependence of the flow stress coupled with low specific heat.4–6 This last “thermal model” is commonly given as the cause for discontinuous yielding. However, the detailed mechanism has not been definitely explained. Particularly, the considerable localized plastic flow that must have occurred before the temperature rises7 can by no means be ruled out, and the available experimental results are quite contradictory.

A yield criterion for Pd 40Ni 40P 20 metallic glass

Numerical methods for porous metals with deformation-induced anisotropy

A coupled dislocation dynamics-continuum barrier field model with application to irradiated materials

The article considers the problem of determining the thermoelastic stresses that arise when drilling a coal seam with a depth of at least 800 m. The stress-strain state is a term that has penetrated from the mechanics of a deformable solid body into various areas, both natural and technological. Usually, three types of stress-strain state are distinguished: the first type of elastic work - up to 35% of the breaking load; the second type of elastic-plastic work - up to 75% of the breaking load, while cracks appear and their number increases with increasing load; the third type of destruction - cracks appear like an avalanche and every detail is destroyed. For the first time, we succeeded in solving analytically the Stefan problem for a cylinder of finite dimensions, with a moving interface, by selecting an integral transformation. A similar solution for a well in coal seams (as well as for other applications) gives an analytical solution to the deformation-wave process in a rock mass, discovered experimentally in the late 70s of the last century (scientific discovery of 1985, priority of 1978). Our experimental and theoretical results fit into the model of macroscopic localization of plastic flow. This model shows that the localization of plastic flow in solids (and in a coal seam) has a pronounced wave character. At the same time, at the stages of easy slip, linear and parabolic strain hardening, as well as at the stage of preliminary destruction, the observed patterns of localization are different types of wave processes.

Non-linear assessment of critical failure modes in the first wall of the European TBM

A macroscopic constitutive law for porous solids with pressure-sensitive matrices and its implications to plastic flow localization