ABSTRACT

The crystalline FEM theory that incorporates Bausinger's effect presented in the previous report has been improved by developing an iterative time integration algorithm. This improved theory is applied to investigate the relationship between the strain hardening properties and the phenomenology of plastic deformation localization and irreversible slip generation, which are part of the fatigue crack initiation process. The investigation is carried out by calculating the deformation behavior of f.c.c, single crystal under cyclic loading conditions.

Following are the results:

  1. Under the conditions chosen for our calculation, the causes of plastic deformation localization and irreversible slip generation are changes in the maximum resolved shear stress, and the deviation of the back stress in the course of the loading cycle. These phenomena are derived from the difference of stress distribution during tensile / compressive loading. Non-uniform residual plastic deformation induced by initial imperfections causes this difference.

  2. Plastic deformation localization and irreversible slip generation arise sooner and proceed more rapidly when strain hardening is larger and / or latent hardening is stronger under the specific conditions chosen.

  3. There are some cases where accumulation of irreversible slip gets saturated when the hardening rate is small. Plastic deformation localization and irreversible slip generation arise only after a large number of cycles when latent hardening is the same as self hardening under the chosen conditions.

1. Introduction

It is generally agreed that plastic strain localization and irreversible slip generation 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. The authors have expanded this theory so that it can analyze cyclic plastic deformation behavior during fatigue process (Tomita et 140 a1.(1997)), and developed a FEM code which takes into account lattice rotation, rate-dependency and Baushinger's effect.

Keywords:
stress amplitude begin, slip system, loading, imperfection, deformation behavior, back stress, loading cycle, time history, cyclic deformation behavior, irreversible slip generation
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1999. The International Society of Offshore and Polar Engineers
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