Measurement of the fatigue crack propagation threshold of fretting induced cracks in Ti–6Al–4V

A unique fatigue specimen was designed from the used fretting pads of Ti–6Al–4V fretting fatigue experiments. Many of these pads contained cracks that initiated and then arrested during the original fretting experiments. Heat tinting was used to mark the crack surface, and stress relief was applied to some specimens to remove load-history effects. The specimens were subjected to high cycle fatigue step testing and the threshold stresses were measured. The measured fretting crack sizes were used to calculate the crack propagation threshold, ΔKth. The results were analyzed for short crack and load history effects. Crack size effects were readily explained with a simple short crack model. No load history effects were noted for these fretting induced cracks.