Fatigue crack growth in AlCu4Mg1 under nonproportional bending-with-torsion loading

We present the experimental results on fatigue crack growth for AlCu4Mg1 aluminum alloy under proportional and nonproportional bending with torsion obtained at the Opole University of Technology. Specimens with square sections and stress concentrators in the form of external one-sided sharp notches were used. The tests were performed in a high-cycle fatigue mode for the stress ratio R = -1 and the phase shift between the bending and torsion loads equal to ϕ = 0, 45° and 90°. Three loading paths were used: line, ellipse, and circle. The fatigue crack growth was cyclically measured with the use of an optical microscope (with a magnification of 25 diameters), strain gauges, and a computer to record the signals of loading. In the tested specimens, it was possible to observe the growth of cracks conforming with the mixed mode I + III. The crack growth was nonuniform on both sides of the specimen surface. However, the difference between the crack lengths was rather small. In the biaxial tests, the influence of bending was six times greater due to the notches in the bending plane. The experimental results are described by range of the stress intensity factor ΔK.