Secondary bending of lap joint designs using digital image correlation and finite element analysis

Lap joints inherently experience a phenomenon known as secondary bending, which is caused by the eccentricity of the fastened sheets with respect to the load path. Within the aircraft structure, the amount of secondary bending is reduced due to the internal stringers and support frame. However, lap joint laboratory test samples are isolated from the main structure and typically experience large secondary bending. This secondary bending can alter the outcomes from mechanical testing, especially for fatigue crack initiation and growth behaviour. It is therefore important to understand the level of secondary bending for various lab test sample designs so that consideration can be made when testing such designs. This study investigates the secondary bending in three lap joint designs using digital image correlation and finite element analysis.