Fatigue life and crack growth direction in 7075-T6 aluminium alloy specimens with a circular hole under biaxial loading

• Published in: International journal of fatigue Vol. 125; pp. 222 - 236
• Main Authors: Chaves, V., Beretta, G., Balbín, J.A., Navarro, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2019; Elsevier BV
• Subjects: Aluminum base alloys; Axial stress; Biaxial loads; Biaxial test; Crack direction; Crack propagation; Cracks; Cycle ratio; Electron microscopes; Endurance limit; Fatigue cracks; Fatigue failure; Fatigue life; Fatigue tests; High cycle fatigue; Materials fatigue; Notch; Optical microscopes; S N diagrams; Torsion; Endurance limit; Biaxial test; Crack direction; High cycle fatigue; Notch
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2019.03.031

•7075-T6 aluminium alloy was subjected to in-phase biaxial fatigue.•The geometry was a tube with a passing through hole.•The S-N curves were constructed and the crack surface was analyzed.•The crack began close to the point of maximum principal stress.•The crack followed the maximum principal stress direction. This work shows the results of a set of tests in 7075-T6 aluminium alloy specimens. The tests were under load control at R=-1. From the tests, the corresponding S-N curves were built, and the endurance limits were calculated for 1 million cycles. The ratio between the pure torsion and tension endurance limits was 0.58, i.e., the behaviour of this material in fatigue is of the von Mises type. Specimens with circular holes of various diameters under tension, torsion and in-phase biaxial loading were tested. The directions of the cracks that grew from the holes were studied with an optical microscope, a scanning electron microscope (SEM) and a non-contact 3D optical profiler. In particular, the points where the cracks began and the direction in which the cracks propagated along the first 150 μm were analysed. In general, the initiation point was close to the maximum principal stress point, and the crack direction was close to the maximum principal stress direction. The endurance limit predictions were close to the experimental results.