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Micropitting is a type of rolling contact fatigue (RCF) associated with rough surfaces and severe lubrication conditions. In the present study, we developed an estimation method for micropitting life. An S-N curve, which is a relationship between micropitting life and stresses acting in the region affected by surface asperities (near-surface stress), is established by using data from RCF tests and estimated histories of near-surface stresses (stress history). Changes in the surface topography and residual stresses including the initial condition are measured in order to estimate the stress history. This enables us to consider the influences of surface topography and residual stresses on micropitting. Micropitting life under an arbitrary operating condition is estimated from the established S-N curve and the estimated stress history up to a finite cycle. It is revealed that micropitting life can be accurately estimated from the established S-N curve within the range of our experiment. The median, minimum, and maximum of the relative life ratio (ratio of actual micropitting life to the estimated life) were 0.89, 0.49, and 1.82, respectively. Further analysis confirms that the accuracy is improved by considering residual stresses.

In order to improve the service life of the artificial acetabular cup in a total hip replacement, it is important to determine the best material and design, and to assess the mechanical behavior around the cup. In this study, electronic speckle interferometry (ESPI) and the two-dimensional finite element method (FEM) are employed to investigate the mechanical behavior. The influence of the cancellous bone and cup thickness on mechanical behavior around the cup was investigated. Good agreement of the cup model was found between the ESPI measurements and FEM predictions. The following results were obtained. (1) Cancellous bone with a porous structure can be measured by the ESPI method. (2) There are discontinuities of the displacement distribution in the transverse direction in each boundary region of the cup, bone cement and cancellous bone. (3) The maximum shear stress exists in the boundary region of the cup and bone cement.

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