Geometry and adhesive optimization of single-lap adhesive joints under impact

The use of composite adhesive joints increased in the last decades through structural applications, comprising the aeronautical and automotive industries. Contrary to the static loading case, in many real situations, adhesive joints are subjected to impact loads, such as in the event of vehicle crashes. Despite this fact, numerical modelling of this loading type is seldom addressed in the literature. This work evaluates the effect of the overlap length (L-O) and adhesive type on the strength of composite single-lap joints (SLJ), when impact loaded, through experimental tests and cohesive zone models (CZM). Two different types of adhesives were tested (Araldite (R) AV138 and Sikaforce (R) 7752), keeping constant the composite adherends with unidirectional lay-up. The joints were subjected to a drop test and validated through the numerical model, by the analysis of stresses and damage, predicting the joints' strength for different geometries and adhesives. It was concluded that the increase of L-O increases the joint strength, especially in those with a more flexible adhesive (Sikaforce (R) 7752), since this type of adhesive prevents significant stress concentrations, and being a ductile adhesive, provides the ability to absorb peak stresses. The impact CZM was able to predict the impact joints' strength with good accuracy.