The Journal of Strain Analysis for Engineering Design

A multiscale methodology for fretting wear–fatigue analysis of a prosthetic hip implant taper-lock assembly is presented. On a macroscopic scale, the stem and cap surfaces are smooth. However, on a microscopic scale, surface roughness undulations are employed to accentuate the frictional contact for an enhanced mechanical locking effect. Macroscopic (global) modelling for fretting wear–fatigue prediction of two head/stem material combinations, namely, Co-28Cr-6Mo against direct metal laser sintering Ti-6Al-4V (Ti64) and forged Ti-6Al-4V, is investigated. The significance of fretting wear and fatigue in a hip joint for 10 years of service in a normal-weight male for moderately intense exercise is predicted for both material combinations. A micro-scale fretting wear–fatigue model of the surface undulation submodel is developed to predict wear and fatigue micro-cracking. A key aspect is the development of a multiscale wear–fatigue algorithm using adaptive meshing. Both material combination joints are shown to have sufficient wear resistance with direct metal laser sintering Ti64 performing better in terms of both fretting wear and fatigue.

Nine methods currently available for estimation of fatigue properties from simple tensile data are discussed in detail. The estimation accuracies of these methods were compared according to the test data of nine types of steam turbine rotor steels. The results showed that the values calculated using the nine methods resulted in unacceptable values. In double logarithmic coordinates, the nine method functions were linearly modified, where the predicted lives were all less than quadruple the observed lives, except for the mixed method. A new method that takes the temperature influence into account is presented, which is suitable for fatigue life estimation of steam turbine rotor steels at high temperature (400 °C–600 °C). The estimation results show that the new method can provide acceptable accuracy.

If a Hertzian contact is loaded by a tangential force which varies direction in time, the classical solution due to Cattaneo and Mindlin does not hold, and a numerical solution is needed. Here, we deal with the important practical case when the force describes an ellipse in the loading space, that is, the components have harmonic variation, with the in-phase (uniaxial) case being the limiting Cattaneo–Mindlin problem. We observe convergence to a steady state within the second cycle of oscillatory loading, and we describe the dependence of frictional dissipation, important both as a source of structural damping and as an indicator of potential fretting damage, on the parameters of the problem. The results show that the dissipation depends significantly on the biaxiality ratio between the tangential load components, particularly so when their amplitude is close to the full sliding limit. We find steady-state dissipation to be higher than the corresponding Cattaneo–Mindlin case for low tangential forces (with a maximum of dissipation for a rotating load). The increase is of the order of 15% only, whereas the decrease for large tangential forces seems to be more significant. This is vaguely similar to the case recently studied when the tangential force was of constant direction, but normal and tangential loads were oscillating harmonically and out of phase: this suggests that in the general case, the dissipation may be significantly larger when all the loads are out of phase.

The investigation of lattice strains has proven to be a viable method for probing the crystal level stress state in deforming polycrystalline samples. Building on the recent availability of high-rate X-ray detectors, we have developed a new technique that combines diffraction data with crystal-based finite element simulations to estimate the lattice strain uncertainty for each measurement. To estimate the uncertainty, we combine the probable number of crystals expected for each measurement with the simulated lattice strain standard deviation. Under this framework, the uncertainty is related not just to the number of diffracting crystals but also to the variability in the lattice strain between these crystals. An estimate of uncertainty for each measurement enables both the investigation of previously inaccessible phenomena where the lattice strain evolution is expectantly small and the application of lattice strain measurement techniques to materials with more complex microstructures. The new approach was demonstrated for an aluminum alloy 7075-T6 sample undergoing uniaxial tensile loading.

Thermal instability of deep spherical shells made of functionally graded material and surface-bonded piezoelectric actuators is studied in this article. The governing equations are based on the classical shell theory and the Sanders nonlinear kinematic equations. It is assumed that the property of the functionally graded materials varies continuously through the thickness of the shell, according to a power law distribution of the volume fraction of the constituent materials. The constituent material of the functionally graded shell is assumed to be a mixture of ceramic and metal. The analytical solutions are obtained for three types of thermal loadings and constant applied actuator voltage. Results for simpler states are validated with the known data in the literature.