مرکز منطقه ای اطلاع رساني علوم و فناوري - ELECTROMAGNETIC FIELDS GENERATED IN METALS BY THE QUASI STATIC PROPAGATION OF ELASTIC-PLASTIC CRACKS

Abstract :

Starting from the well-established fact that the electric potential in metals round a dislocation is proportional to the associated lattice dilatation, we obtain by superposition the electric potential due to an isolated crack and a crack associated with a crack-tip plastic zone and a dislocation-free zone in between (elastic-plastic crack). We assume mode I loading in a linear isotropic elastic medium. The electric potential and associated electric field thus obtained, depend implicitly on time through the variation with time of the applied stress, crack length and size and location of the plastic zone. It is then possible, using Maxwell s equations, to obtain expressions for the induced magnetic field, Poynting’s vector and intensity of the electromagnetic wave. We further restrict ourselves to quasi static propagation of the isolated crack assuming the Griffith condition G= 2γ (G is the crack extension force and γ the surface energy) to hold at any time. Expressions and graphical representations of the various electromagnetic quantities are given; their explicit dependences with respect to various parameters including crack extension velocity and surface energy are revealed. The present study applies to pure metals. However, because an expression of the lattice dilatation is also obtained, this latter result can be used in any other material where an electric field is produced by an inhomogeneous dilatation of the lattice. The case of ice is discussed and it is indicated how an analysis, taking account of crack-tip plasticity, could be conducted. Finally, the weakness in certain models devoted to the emission of electromagnetic radiation during plasticity and fracture in metallic materials is stressed.