The influence of magnetic field on the nucleation of micro crack for brittle fracture is studied. The dynamic equation of micro crack in magnetic field is deducted. Using the crack model of a single pile-up group of dislocation, the growth speed of micro crack at a low growth speed stage is derived. To understand the effect of the magnetic field on the nucleation, the mean nucleation rate of micro crack in magnetic field is obtained. The derived result on the mean nucleation rate of micro crack shows that the applied magnetic field could change the mean nucleation rate of micro crack. The way in which the mean nucleation rate varies with the field depends not only on the field but also on the magneto properties of material.

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Liu Zhao-Long( ), Hu Hai-Yun( ), Fan Tian-You( ), and Xing Xiu-San( )

This paper develops the non-equilibrium statistical fatigue damage theory to study the statistical behaviour of micro-crack for metals in magnetic field. The one-dimensional homogeneous crack system is chosen for study. To investigate the effect caused by magnetic field on the statistical distribution of micro-crack in the system, the theoretical analysis on microcrack evolution equation, the average length of micro-crack, density distribution function of microcrack and fatigue fracture probability have been performed. The derived results relate the changes of some quantities, such as average length, density distribution function and fatigue fracture probability, to the applied magnetic field, the magnetic and mechanical properties of metals. It gives a theoretical explanation on the change of fatigue damage due to magnetic fields observed by experiments, and presents an analytic approach on studying the fatigue damage of metal in magnetic field.