Effect of Bonding Technique on Debonding of Complex Composite Skin/Stringer Configuration

Delamination/Debonding is one of the predominant forms of failure in laminated composite structures, especially when there is no reinforcement along the thickness. To utilize composite structures that are more damage tolerant, it is necessary to understand how delamination or debonding develops, and how it can affect the residual performance of the parent structure. A number of factors such as residual thermal stresses, matrix-curing shrinkage and manufacturing defects affect damage growth in a composite structure. It is important to assimilate which manufacturing or assembling technique fits the best. The objective of the current work is to identify the best joining technique for an un-symmetric lambda shape complex stringer, in order to avoid or delay debonding of skin-stiffener composite specimens. Adhesive bonding and Co-curing/Co-bonding is investigated through three-dimensional finite element analyses. Commercially available software HYPERMESH and ANSYS were used to do the 3D meshing and analysis. Adhesive bonded structure was analysed by contact analysis and co-cured structure was analysed by cohesive zone modelling technique (CZM). Under multi-axial loading, adhesive bonded configuration showed larger stresses compared to co-cured configuration. The former skin-stringer configuration de-bonded 83.8% more than later in normal direction and 61.04% in x-direction. It is concluded that for unsymmetrical lambda shape stringer, under given multi-axial, co-curing is the best method of manufacturing.