The crack propagation behavior in fretting-fatigue of A2024-T3 strip-typed specimens was investigated under the repeated stress of 60MPa with three different stress ratios, namely
R=0.33, 0, and -0.33, and the contact pressure of 50MPa. The crack length
a, the effective stress intensity factor range Δ
Keff proposed by J. Schijve, and the maximum stress intensity factor
Kmax were plotted as a function of crack propagation rate
da/
dN. It was seen that the crack propagation behavior in fretting-fatigue was affected by the stress ratio, and was able to be divided into two stages. In ‘S
I-stage’ where the crack length is up to about 0.5mm, the
da/
dN in fretting-fatigue was very high compared with that in unfretting-fatigue, but with crack growth the
da/
dN in fretting-fatigue decreased markedly in the order of decreasing
R. In ‘S
II-stage’ the
da/
dN in fretting-fatigue increased with crack growth, and was higher than that in unfretting-fatigue for
R=0.33, lower for
R=-0.33, and almost the same for
R=0. This behavior was interpreted by the reduction of fretting effect with crack growth and by the crack surface contact due to slantwise crack characterized in fretting-fatigue and shear lips characterized in A2024-T3.
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