Fatigue Crack Growth Behavior of Aluminum Alloy under Repeated Two-Step Load Conditions
The Case where Both Stress Levels KH and KL are in Region II of Crack Growth Rate Curve
1987 Volume 36 Issue 411 Pages 1368-1374
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1987 Volume 36 Issue 411 Pages 1368-1374
Aluminum alloy (A2017-T3) compact tension specimens were tested under repeated two-step load conditions, and the crack growth rate and crack closure behavior were observed. The higher and lower stress levels, KH and KL, were selected in the region II of the crack growth rate curve of the material obtained by ΔK increasing tests. It was found that the crack growth rate da/dN and crack opening stress intensity Kop were affected by the stress cycle ratio KL/NH; namely, da/dN was decreased and Kop was raised by the increase of NL/NH. The estimation of the crack growth rate for lower stress level KL by the linear cummulative law shows that the estimated relation of (da/dN)L versus (Keff)L was in better agreement with the fundamental crack growth rate curve when the crack closure only in the repetition of KL was taken into account, than when the closure at both stress levels of KH and KL were considered.
