The effects of adherend thickness on the fatigue strength of adhesively bonded single-lap joints

Abstract

Different adhesive bonding methods have been prominently used in aerospace applications since the 1980s because adhesively bonded joints are regarded as an alternative to traditional bonding methods. However, the effects of fatigue on adhesively bonded joints – one of the most significant issues in the aerospace industry – are still currently being investigated. This study experimentally 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 DP460 structural adhesive – under varying tensile fatigue loads. Accordingly, before performing fatigue tests, static tensile strength tests were carried out on the SLJs to determine the maximum loads to be used for tensile fatigue tests and also to evaluate their quasi-static performances. The fatigue tests were performed at a loading ratio (R) of 0.1 and a frequency of 20 Hz. The static tensile strength of the joints was found to increase by approximately 22% with increasing adherend thickness. However, this increase was not the same as the increase in adherend thickness. In addition, increased adherend thickness was observed to change the maximum load applied to the joints over infinite cycles (taken to be 106 cycles). This was because the change in adherend thickness changed the bending moment formed in the joint and the flexural rigidity of the adherend.