Fretting fatigue life prediction is a strategic issue for modern industry. Accurate prediction of total lifetime depends on crack nucleation time prediction. However, fretting fatigue is characterized by a high stress gradient which overestimates cracking risk at the hotspot. Hence non-local analyses are required. The present study focused on the critical distance method. However, no defined method is currently established to obtain this value, which has been shown to depend on microstructure or stress gradient. The present study investigated the influence of incipient crack length on critical distance crack nucleation prediction. An optimal ℓopt-bopt condition was introduced enabling accurate prediction of the crack nucleation condition whatever the loading condition. This approach was then applied to fretting endurance experiments, allowing to correlate fretting cracking endurance with shear fatigue data. Finally it was used on fretting fatigue lifetime experiments, showing good endurance prediction.
The potentiality of composition graded AlMgSi wires for optimized combination of electrical conductivity and torsion strength has been investigated. Composition graded wires were obtained by co-drawing commercially pure Al with an AlMgSi alloy followed by diffusion annealing. Diffusion gradients and local hardening response to precipitation treatments were evaluated thanks to nanoindentation measurements. Resulting microstructures with spatial gradients of nanoscaled precipitates were characterized by transmission electron microscopy. Finally, it is shown that such graded structures give rise to an improved combination of electrical conductivity and mechanical strength in torsion as compared to the predictions based on a classical rule of mixture.
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