The effects of using intermittent metal part reinforcement and countersink on the strength of adhesively bonded joints

This study investigates the impact of two innovative methods, namely, intermittent metal part reinforcement and countersinking, on the strength of single lap joints (SLJs). In the former method, metal inserts are strategically integrated within the adhesive layer, while the latter involves the application of countersinks on the adherends to create conical depressions for adhesive application. The metal inserts and countersink samples were fabricated using a 5-axis CNC milling machine. Subsequently, the joints were produced by subjecting the samples to 0.15 MPa pressure and 70 °C temperature for 120 min with the aid of a hot press. Tensile tests were conducted on single lap joints (SLJs) featuring five different configurations of intermittent metal part reinforcement joints (IMRJs) with varying sizes and positions of reinforcements, as well as six countersunk reinforced joints (CRJs) with different orientations of countersinks, all while keeping the width and overlap length constant. A two-dimensional finite element (FE) model of the IMRJ was constructed using ABAQUS software, incorporating cohesive zone elements to simulate the behavior of the adhesive layer (DP 460). The model's accuracy was confirmed through experimental verification. Additionally, fractographic analysis of the failure surfaces of both types of joints was carried out. The inclusion of IMRJs and CRJs in the SLJs increased their load-carrying capacity by more than 10 % and 30 %, respectively.