A crystalline FEM theory is applied to investigate the relationship of the crystal geometry to the progress of plastic deformation localization (P.D.L.) and irreversible slip generation (LS.G.), which are part of the fatigue crack initiation process, by calculating the cyclic deformation behavior of a FEM model of a f.c.c, crystal which reproduces the restriction caused by the neighboring grains. As results, the followings are found: 1) In the same manner as the results for f.c.c, single crystal analyzed in the previous reports, P.D.L. and |.S.G. in a grain whose deformation is restricted by the neighboring grains can be simulated by using the crystalline FEM theory developed by the authors. 21 Under the conditions chosen, P.D.L. and |.S.G. proceeds very rapidly only when all of the following conditions are satisfied: a) loading direction is planer or coplaner double slip direction; b) the slip directions of the primary and conjugate systems meet the free surface at the same angle; c) the slip planes of the two systems meet the free surface at the same angle. 3) Under the conditions chosen, the progress of P.D.L. and I.S.G. has a high sensitivity to the difference of the geometrical relation of the slip systems to the free surface. The sensitivity of the progress of P.D.L. and I.S.G. to the misalignment of the loading axis is lower than the one to the geometrical relation of the slip systems to the free surface.
It is generally agreed that plastic strain localization and irreversible slip generation (we abbreviate these phenomena to "P.D.L." and "I.S.G.' in this report.) are part of the fatigue crack initiation process, and that in order to explain the process, it is necessary to examine the microscopic mechanisms of these two phenomena.
