Study of ratcheting by the indentation fatigue method with a flat cylindrical indenter. Part II. Finite element simulati
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e finite element method (FEM) was used to study the flat cylindrical indentation fatigue behavior using a kinematic hardening model (A-F model). This study was motivated by the experimental work of the preceding paper [B.X. Xu and Z.F. Yue, J. Mater. Res. 21, 1793 (2006)], in which there were obvious similarities in the behavior of conventional fatigue specimens and indentation fatigue specimens. It is proposed that the A-F model can predict the indentation fatigue behavior. Generally, the experimental behavior of the indentation fatigue testing can be explained by the FEM analysis. In addition, the effect of residual stress on the indentation depth per cycle was studied. The effect of friction between the indenter and the specimen and evolution of von Mises stress beneath the indenter was also investigated. Numerical results showed that the effect of friction on the indentation depth propagation can be neglected. Further analysis showed that the steady-state indentation depth per cycle increases with increasing compressive residual stress and decreasing tensile residual stress. I. INTRODUCTION
The phenomenon of ratcheting, as it occurs in cyclical hardening and softening materials under cyclic loading, has received considerable attentions in recent years. The case of cyclic plasticity and cyclic viscoplasticity and the effects of complex multiaxial loadings have been considered.1–12 Kapoor investigated the relationship between plastic ratcheting and wear and proposed a ratcheting wear mechanism.13 Kapoor and Johnson identified two ways to drive the mechanisms of plastic ratcheting.14–16 However, their model concentrated on the evaluation of the material damage and erosive wear behavior resulting from the plastic ratcheting and the effect of the plastic ratcheting on lifetime.13–16 Up to now, most experiments have been performed under tension–compression or tension–torsion cyclic loading using standard fatigue specimens (e.g., round bars). The standard fatigue specimen requires a large volume of material. In some cases (e.g., cast turbine blades), experimental results from the standard fatigue specimens do not always reflect the mechanical properties of the serviced materials. As an alternative testing method, indentation testing technology is useful because of its fast, simple, precise, and non-destructive merits (e.g., Refs. 17–22). Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2007.0019 186
J. Mater. Res., Vol. 22, No. 1, Jan 2007
In Part I of this paper, a series of tests were performed to explore ratcheting phenomenon in annealed copper by the indentation method using a flat cylindrical indenter.23 The experimental results showed that the indentation depth–cycle curves were analogous to the conventional strain–cycle curve of uniaxial fatigue testing, which has a primary stage of decaying indentation depth per cycle followed by a secondary stage of nearly constant rate of indentation depth per cycle. It is found that the steadys
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