High cycle fatigue of fretting induced cracks
Abstract
The objective of this study was to quantify the effect of fretting fatigue stress histories on fatigue crack growth and the fatigue crack growth thresholds due to High Cycle Fatigue (HCF) loading. The approach used to meet this objective consists of both experimental and analytical studies with the experimental results helping to verify the analysis. Test pieces from Ti-6Al-4V fretting fatigue experiments were examined and fatigue tested. The first type of experiment involved interruption of the fretting fatigue experiment prior to failure followed by continued fatigue testing of the specimen under remote loading without fretting. The crack growth and coalescence of the fretting cracks located at the edge of contact was recorded and compared to fracture mechanics analysis. The analysis conservatively predicted the growth to failure in these specimens. For the second type of experiment a unique fatigue specimen was designed from the fretting pad used in the fretting fatigue experiments. This fretting pad was subject to high local contact stresses that could initiate cracks, but they would not propagate to failure due to the lack of a bulk cyclic tension. The fatigue crack growth thresholds of these fretting cracks were measured by step testing. The cracks were measured from the fracture surface after failure with the aid of heat tinting. The measured fatigue crack growth thresholds of these cracks were consistent with a small crack threshold model. Many of the specimens were stress relieved prior to testing to eliminate load history effects and ultimately no fretting load history effect on the threshold was conclusively observed. Crack initiation, propagation, and threshold models were applied to the results of the experiments conducted for this research with mixed success. These models were then applied to the fretting fatigue experiments performed by other researchers. Stress life and constant life diagrams were created and compared well with the experimental data. The affect of various fretting load parameters on the fatigue life and threshold predictions was investigated.
Degree
Ph.D.
Advisors
Grandt, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering
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