Effect of Multiaxial Loading on Crack Growth. Volume 1. Technical Summary

Fatigue Crack Growth Under Biaxial Loading

“…Test data for 2024-T3 aluminium generated by Liu and Dittmer [6] were chosen for the present investigation and details of the tests are found in that reference. A cruciform specimen configuration was used with an overall length of 597 mm and a thinner region, 152.4 mm in diameter and 4.51 mm in thickness, in the centre of the specimen.…”

“…The following equations will be used for the calculation of mode I and mode I1 stress intensity factors [18]. The same equations were also used in [6]. Hence with reference to Fig.…”

“…Hence with reference to Fig. 1: F,y, FZy, F,, and F,, are functions of u and are standard terms given in reference [6]. The definitions for ax, a,.…”

“…Linear elastic fracture mechanics predicts that the component of stress parallel to the crack does not contribute to the singular terms and thus has no effect on fatigue crack growth. However, experimental evidence has provided conflicting indications; the effect of an applied static or cyclic tensile stress parallel to the crack is sometimes considered to increase, decrease or have no effect on the growth rate [1][2][3][4][5][6][7][8][9][10]. Similar conflicting observations were reported for the application of a compressive stress parallel to the crack [4-113. One of the factors responsible for these anomalies is that nominal stress for each arm of a cruciform specimen are used for the correlation of experimental data.…”

“…For a cruciform specimen, the nominal stress in the x-direction could introduce a local stress in the y-direction, and vice versa. When local stresses, such as those at the centre of an uncracked specimen, were used for correlation purposes, the effect of different biaxial stress ratios on crack growth rate was found to be small [4,6,7,10]. However, it must be noted that even with the so-called local stresses they are reference stresses only.…”