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The paper presents the results of tests on the fatigue crack growth for a constant moment amplitude under combined bending with torsion in the aluminium alloy AW-2017A-T4. The tests were performed under different values of the load ratio R. Plane specimens with stress concentrators in form of the external one-sided sharp notch were tested. A non-uniform fatigue cracks growth on both lateral surfaces of specimens was observed during experimental tests. Fatigue cracks were developing in the specimens in two stages; quarter-elliptic edge cracks were observed at the beginning, then evolving into through cracks.

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Abstract:The paper presents an analysis of the state of stress and crack tip opening displacement (strain) in specimens with rectangular cross-section subjected to torsion and combined bending with torsion. The specimens were made of the EN AW-2017A aluminium alloy. The specimens had an external unilateral notch, which was 2 mm deep and its radius was 22.5 mm. The tests were performed at constant moment amplitude = = 15.84 Nm and under stress ratio = -1. The exemplary results of numerical computations being obtained by using the FRANC3D software were shown in the form of stress and crack tip opening displacement (CTOD) maps. The paper presents the differences of fatigue cracks growth under torsion and bending with torsion being derived by using the FRANC3D software.