The effect of damage accumulation in slip bands on the resonant behavior in the very high cycle fatigue (VHCF) regime

摘要

In many applications structural components are cyclically loaded up to a very high number of loading cycles due to high frequency or long product life.In this regime,particular attention is paid to the period of fatigue crack initiation and thus the localization of plastic deformation.The characterization of the damage accumulation in the VHCF regime is conducted by a new approach based on the resonant behavior of the specimen.The resonant behavior of a metastable austenitic stainless steel (AISI304) is studied experimentally in the VHCF regime and shows a distinct transient characteristic.To obtain a physically-based understanding of this characteristic,the underlying microstructural damage mechanisms and their influence on the resonant behavior are modeled.Microscopic examinations indicate that AISI304 executes localization of plastic deformation in planes/bands of intense slip.Therefore,a microstructural simulation model is proposed which accounts for the damage mechanisms of slip bands as documented by the experimental results.The model describes the behavior of slip bands taking the mechanisms of formation,sliding,slip irreversibility and cyclic hardening into account.In order to run simulations considering the real microstructure,the model is implemented into a numerical method.The two-dimensional (2-D) boundary element method is well suited for this purpose and is based on two integral equations: the displacement boundary integral equation applied to the external boundary and the stress boundary integral equation used in slip bands.Fundamental solutions within these integral equations represent anisotropic elastic behavior.By using this method,a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain.The resonant behavior is characterized by evaluating the force-displacement hysteresis loop and using a hysteretic damping model.Results show that simulation of slip bands is in good agreement to microscopic examinations and that plastic deformation in slip bands influences the transient characteristic of the resonant behavior.