Short fatigue crack growth behaviour in Al 5083 alloy

Abstract

This work presents the results of a study of fatigue crack growth in Al 5083 alloy starting from a micro corner notch of 40 μm depth in both directions. The fatigue tests were carried out with constant load amplitude in tension and in bending using three ratio values R = −1, 0.05 and 0.5. The crack aspect ratio a/c evolution as a function of the normalized crack depth, a/ B, was influenced neither by the stress ratio nor by the type of loading for values of a/ B 0.1. Threshold fatigue values obtained for short cracks were found to be lower than for long crack levels, obtained in previous work for R = 0.05 and 0.5. For R = −1 the short fatigue crack threshold value was approximately the same as the long fatigue crack threshold obtained with compact tension (CT) specimens for R = 0.8. Crack opening values were obtained previously with CT specimens using an Elber type micro gauge and were used to calculate Δ K eff values. When comparing the results obtained in this work for short fatigue cracks with the da d N−ΔK eff curves recorded for long cracks, it is concluded that in short cracks the crack opening values may be virtually nil in order to explain their higher crack growth rate.