Material and adhesive effect in adhesively-bonded composite stepped-lap joints
R.F.N. Brito, R.D.S.G. Campilho, R.D.F. Moreira, I.J. Sánchez-Arce
Abstract
Adhesive bonding is a predominant bonding technique in the aeronautical and automotive industries. Cohesive zone models, used together with the finite element method, are a viable tool to predict the strength of adhesive joints. The main objective of this study is to evaluate experimentally and numerically (by cohesive zone model) the mechanical performance of carbon-fiber reinforced polymer stepped-lap bonded joints submitted to tensile loads, for different overlap lengths ( L O ) and adhesives. The failure mode analysis showed a predominant failure type for all adhesives and good correspondence with the numerical predictions. Normalized peel ( σ y ) and shear ( τ xy ) stresses in the adhesive highly increased with L O , which then reflected on different maximum load ( P m ) evolution with L O , depending on the adhesive's ductility. The damage variable SDEG (stiffness degradation) was also evaluated and emphasized on the smaller damage zone at P m for the brittle adhesive. A significant geometry and material effect were found on P m of the stepped-lap joints, with benefit for large L O . In this regard, cohesive zone model revealed to be a suitable tool in determining the behavior of different joints. Comparison with joints with aluminum showed that, provided that no carbon-fiber reinforced polymer delamination occurs, stepped-lap joints between carbon-fiber reinforced polymer adherends give better results due to the higher composite stiffness.