МОДЕЛИРОВАНИЕ ВОЗДЕЙСТВИЯ ВЫСОКОЭНЕРГЕТИЧЕСКОГО ИМПУЛЬСНОГО ЭЛЕКТРОМАГНИТНОГО ПОЛЯ НА МИКРОТРЕЩИНЫ В ПОЛИКРИСТАЛЛИЧЕСКОМ МЕТАЛЛЕ

Abstract

The paper studies electroplastic effect in terms of the hypothesis of the healing of defects in the material under the influence of high-energy pulsed electromagnetic fields. The processes occurring in the metallic samples under the impact of electrical current of high density are considered. The electric, temperature fields, stress-strain state and phase transformations in the vicinity of micro-defects with line size 10 microns are studied. Such defects are always present between the grains in a polycrystalline metal after metallurgical casting or appear in it during its deformation under processing. The coupled quasi-stationary model of the impact of high-energy electromagnetic field on the pre-damaged electroplastic material with an ordered system defects are proposed. The model accounts for melting and evaporation of the metal and the dependence of its physical and mechanical properties on the temperature. The problem is solved numerically by finite elements method with adaptive mesh using on the base of alternative Euler-Lagrange’s method. The boundary value problem is solved for a representative element material with a micro-defect in the case of plane strain. The micro-defects in the form of flat cracks with rounded tips are considered. The presence of micro-cracks leads to inhomogeneous physical and mechanical fields in the material. Numerical modeling has shown that in the vicinity of the micro-defects intensive electromagnetic field and current with large fields gradients arise. This causes rapid local heating in the vicinity of the tip of the micro-crack, followed by thermal expansion of metal, and subsequently melting the material. The inhomogeneous heating results in a high compressive stresses and intense plastic flow of the material in the vicinity of micro-crack. The resulting stress field is not only closing the shores of micro-crack, but also reducing its length and ejecting the metal into the crack. Ejection occurs through the formation of the metal jet of molten metal directed into the crack. These processes may be accompanied not only by melting in the vicinity of the tip, but also evaporation of the metal to crack for the micro-cracks located near the outer boundaries of the sample. The simultaneous reduction in the length, the ejection of the molten metal into the cracks and closing of micro-crack shores leads to the fact that the shores of the crack come into contact with the jet stream and finally the jet material completely jams shores cracks. It is the welding of the crack and healing of the micro-defects which takes place.