Damage evolution in adhesive joints subjected to impact fatigue

There is increasing interest in the effects of low-velocity impacts produced in components and structures by vibrating loads. This type of loading is known as impact-fatigue. The main aim of this paper is to investigate the behaviour of adhesive joints exposed to low-velocity impacting, to study the impact-fatigue life and to compare this loading regime with standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). To this effect, bonded aluminium single lap joints have been subjected to multiple impacting tensile loads and it has been shown that this is an extremely damaging load regime compared to standard fatigue. Two modifications of the accumulated time-stress model have been proposed to characterise the impact-fatigue results presented in this paper. The first model has been termed the modified load-time model and relates the total cumulative loading time of the primary tensile load wave to the mean maximum force. The second model attempts to characterise sample damage under impact-fatigue by relating the maximum force normalised with respect to initial maximum force to the accumulated loading time normalised with respect to the total accumulated loading time. This model has been termed the normalised load-time model. It is shown that both models provide a suitable characterisation of impact-fatigue in bonded joints.