The fracture load analysis of different material thickness in adhesively bonded joints subjected to fully reversed bending fatigue load

The adhesive joints used in airframe and wing sections of aircrafts are generally subject to dynamic (fatigue) loading rather than static loading due to environmental conditions. The dynamic loading formed on wing sections of aircraft is generally in the form of fully reversed fatigue. This study experimentally and numerically investigated the lifetimes of single-lap joints (SLJs) of five different adherend thicknesses (2, 3, 4, 5 and 6 mm) - obtained using AA2024-T3 aluminum alloy and Araldite-2015 structural adhesive - under fully reversed bending fatigue loads. Accordingly, before performing fatigue tests, static bending strength tests were carried out on the SLJs to determine the maximum loads to be used for bending fatigue tests and also to evaluate their static performances. Fatigue tests were performed at a loading ratio (R) of -1 and a frequency of 4 Hz. It was determined that the static bending strength of the joints increased by approximately between 43% and 74% with increasing adherend thickness. However, this increase was not the same as the increase in material thickness. In addition, the increased adherend material thickness changed (decreased or increased) the maximum load applied to the joints over infinite cycles (taken to be 2 x 105 cycles). This was because the change in material thickness changed the bending moment formed in the joint and the flexural rigidity of the material.