Pages 95-107
We have to acquire knowledge about the microscopic deformation mechanisms under cyclic loading condition in order to improve a prediction method of the crack initiation or failure life. In such studies, it is helpful to compare the simulated macroscopic deformation behavior derived from the dislocation models and stress-strain relation of real materials obtained in fatigue tests. We have been developing a crystalline elastic-plastic FEM code which can calculate macroscopic stress-strain response under cyclic loading conditions. In this report, a FEM code for cyclic plastic deformation which can consider lattice rotation and rate-dependency is developed. Using this code, the ununiform deformation behavior of a f.c.c. cubic single crystal under cyclic loading condition is investigated. Results of the analyses are summarized as follows. 1) Although it is assumed that the strain hardening of slip systems depends only on back stress (that is, fully kinematic hardening is assumed), the deformation modes under tension and compression loading are different. 2) The deformation mode changes during loading history. There is a tendency that the local plastic strain intensity becomes more obviously as the number of cycles increases. It is assumed that this mechanism is connected with the generation of P.S.B (persistent slip band), which is the birthplace of fatigue cracks.
