MODELING THE HEALING OF MICROCRACKS IN METAL STIMULATED BY A PULSED HIGH-ENERGY ELECTROMAGNETIC FIELD. PART II

Abstract

The article investigates the processes of transformation and interaction of defects, such as plane microcracks with linear dimension of the order of 10 μm that occur in materials when metal samples are treated by short-term pulses of high-density electric current. The investigation is made numerically based on a coupled model of intense electromagnetic field impact on a predamaged thermoelastoplastic material with defects. The model allows for melting and evaporation of metal as well as the dependence of all physicomechanical properties of it on temperature, as was presented in Part I of this article. The solution of the resultant system of equations is sought by the finite-element method on moving meshes, using a arbitrary Euler–Lagrange method. The calculations showed that as a result of simultaneous decrease of the length, release of the molten metal to the crack, and closing of the edges, the crack edges begin contacting the jet of molten metal and, at the end of these processes, the jet is fully enclosed by the crack edges. Thus, the application of current pulses leads to the welding of the crack and the healing of microdefects. In the present work we consider the problems of choosing the preferable integration domains and the conditions at their boundaries when the above processes are simulated. The way in which the processes under consideration depend on the boundary conditions that can be used in the model is investigated. The effect of the distance between the microcracks and of their mutual position relative to each other on the processes of their healing is studied. Numerical simulation showed that in studying the processes microcrack healing it is possible to restrict oneself, without loss of accuracy, to consideration of one representative cell as the integration domain (or one-fourth of the symmetric representative cell) by specifying at its boundaries, that are not the axes of symmetry, the difference of potentials determined for the cell without defect (in the state "unperturbed" by the presence of a microcrack). In such case, the conditions of symmetry can be selected as the mechanical boundary conditions. When the distances between the cracks exceed 5–6 lengths of the cracks, the processes of healing will occur identically, irrespective of whether they are simulated in the integration domain composed of one or several representative cells. Decreasing the distances between the cracks to 1–2 linear dimension of the cracks (taking into account changes in their mutual position) does not change qualitatively the described process of healing; however, this results in substantial slowing down of the process: the release of the molten material to the crack continues, but the decrease of the crack reduces significantly, especially in the lateral direction.