Residual stress near fillet and roller fatigue in crankshaft fillet rolling process.

摘要

A generalized anisotropic hardening rule based on the Mroz model for pressure insensitive and sensitive materials is derived. The evolution equation for the active yield surface is obtained by considering the continuous expansion of the active yield surface during the unloading/reloading process. Then, the incremental constitutive relation for a general yield function is derived based on the associated flow rule. The anisotropic hardening rule can be used to obtain closed-form solutions for stress-strain relations under proportional cyclic loading conditions. Next, the implications of the anisotropic hardening rule in the cyclic plastic behavior of pressure-sensitive materials are explored based on non-associated flow rules. A new non-associated flow rule is suggested in order to obtain one-dimensional closed hysteresis loops for pressure-sensitive materials as observed in experiments.; The cyclic plasticity theory is employed in a two-dimensional plane strain finite element analysis of crankshaft fillet rolling in order to obtain the stress distributions near the fillet during the fillet rolling process. The anisotropic hardening rule gives more compressive residual hoop stress than the nonlinear kinematic hardening rule. The magnitude of compressive residual hoop stress near the fillet surface decreases as the pressure sensitivity of yielding increases. The computational results appear to agree with the experimental observations in bending fatigue tests of crankshaft sections.; The effects of roller geometry on the fatigue of roller and the residual stresses near the fillet are also investigated based on a two-dimensional finite element analysis of fillet rolling process in order to improve the fatigue lives of rollers. An appropriate adjustment of the roller geometry can significantly improve the fatigue lives of rollers without a significant change of the fatigue performance of crankshaft sections under bending loads. The effects of notch depth on the natural frequency drop of a resonant bending system with a notched crankshaft section are investigated experimentally, numerically and analytically. The information on the frequency drop for a given notch depth from the results can be used as a guide to infer the extent of fatigue crack depths in resonant bending fatigue tests of crankshaft sections.