Influence of large pre-straining of aluminium alloys on their residual fatigue resistance

The aim of this experimental study is to quantify the influence of a tensile pre-strain on the residual fatigue life of aluminium alloys. Two alloys with different chemical compositions and hardening modes have been investigated: 2017A-T3 used in the aircraft industry and 5454-O used in automotive applications. The pre-loadings were carried out with two strain rates (quasi-static and impact) and for several controlled elongations. The residual fatigue life was estimated under a level which corresponds to about 2 × 105 cycles for the undamaged material. From this study, two conclusions have been highlighted. The pre-strain rate does not have any influence on the residual material behaviour, whereas each material has a different strain rate sensitivity. The material aspect seems to be fundamental: the Al–Mg alloy (5454-O) which is a solid solution hardening alloy remains insensitive to all pre-loading whereas the Al–Cu alloy (2017A-T3) which can be age hardened, undergoes a large decrease in fatigue performance after pre-strain.