Comments to the paper: Fatigue crack growth and life predictions under variable amplitude loading for a cast and wrought aluminum alloy

摘要

In a recent paper, Glancey and Stephens applied the FASTRAN-II implementation of the strip yield model to predict fatigue crack growth in two aluminium alloys: D357 and 2024-T3. The model performance was evaluated based on comparisons between the predictions and the fatigue test results. For either material, the following variable amplitude loading conditions were considered: (i) single overload with the stress ratio R = 0.1, (eight different load cases: four overload ratios, OLR, and two levels of the baseline cycle stress intensity factor range, DELTA K_(ss)), (ii) single periodic overloads (OLR = 1.75) applied every 2500 cycles (two DELTA K_(ss) levels, R = 0.1), and (iii) a random flight simulation spectrum applied at two initial K_(max) levels. The DKEFF code available in the FASTRAN software has been used to convert the constant amplitude test data da/dN vs. AK obtained at a single stress ratio only (R= 0.1) into the da/dN vs. DELTA K_(eff) data required in the FASTRAN material input file. For either material, three different concepts of the constraint parameter referred to in the paper as the Constant Constraint, Fracture Surface and Flow Stress approach have been used in DKEFF, which resulted in generating three different input files and, hence, in three sets of the corresponding predictions.