Design of co-cured single and double lap joints with carbon fiber-epoxy composite and steel adherends

Abstract

A co-cured joint, whose curing and bonding processes are achieved simultaneously and whose adhesive is the excess resin extracted from composite materials during consolidation, has several advantages compared to the adhesively bonded joint because of its manufacturing simplicity. The co-cured joint requires neither adhesive nor surface treatment of the composite adherend. There are many bond parameters to affect the strength of co-cured lap joints, namely surface roughness of the steel adherend, stacking sequence of the composite adherend, bond length, and manufacturing pressure in the autoclave during bonding process. In this paper, the joint strength of plate-type co-cured single and double lap joints with steel and carbon fiber-epoxy composite adherends was experimentally investigated through static and cyclic tensile load tests with respect to several bond parameters. Experimental results were explained with respect to the bond parameters through investigating failure surfaces on the steel adherend and lots of data from static and cyclic tensile tests. Based on the stress distribution of the co-cured single and double lap joints obtained through finite element analyses, tensile load bearing capacities were calculated considering two different failure models, the Ye-delamination failure criterion and the three-dimensional Tsai-Wu failure criterion. Finally, optimal conditions of the co-cured single and double lap joints to obtain more efficient mechanical characteristics were presented. As another approach method to estimate the failure of the co-cured lap joints, formulation based on the fracture mechanics approach was also developed. The eigenvalue problem was used to determine asymptotic stress and displacement fields near the interface corner between anisotropic and isotropic adherends. Three examples related to the calculation of the order of the stress singularity at the interface corner of the anisotropic/isotropic bi-material were presented. For obta...