Effect of bonding area geometry on the behavior of composite single lap joints (SLJ) and estimation of adhesive properties using finite element method

ABSTRACT

In this study, the mechanical behavior of Single Lap Joints (SLJ) subjected to tensile loading was investigated both experimentally and numerically by considering different SLJ sizes including adherend thickness (T:0.88, 1.76, 3.52 mm), joint width (W:10, 20, 30 mm), and overlap length (L:10, 20 mm). A polyurethane adhesive and carbon fiber composite adherends were used for the experimental activity. The experimental campaign was carried out to assess the effects of the SLJ geometry on the mechanical behavior of SLJ. Further, SLJ tests were used to estimate the fracture toughness in mode I and II by using Finite Element methods (FEM) coupled with optimization analysis. The results showed that all three parameters strongly change the load capacity of the joints. According to the Experiments, for every sample configuration, the higher the adherend thickness the higher the adhesive shear and the lower the substrate normal stresses. Moreover, the width showed negligible effect on adhesive shear and substrate normal stresses. Numerically, the effect of geometric parameters has been analyzed once at relative 25% of ultimate load and once at a fixed load for each sample. At 25% of ultimate load, it was observed that the increase in the joint width has nearly no significant effect on adhesive shear and peel stresses. However, at a fixed common load increasing L, W, and T resulted in a decrease in adhesive shear and peel stresses. A good agreement was found between the experimental and numerical results.

KEYWORDS:

• Composites
• single lap joint
• polyurethane adhesive
• fracture toughness estimation

Acknowledgement

The research work was carried out in a PhD program partially funded with a scholarship by J–Tech@PoliTO–Advanced Joining Technologies. The authors would like to thank Andrea Bergamelli and Lorenzo Stilo from Sika Italia S.p.a. for their availability in supporting this research and for providing the adhesives.

Disclosure statement

No potential conflict of interest was reported by the author(s).