Volume 2, Issue 8 (September 2005)
Stress Analysis of Asymmetric Co-Cured Stepped-Lap Joints
Manufacturing of large adhesively-bonded structural joints in the marine composites industry requires careful design and manufacturing to ensure durability of the joint. When the adherends to be joined are both fiber-reinforced laminates, an alternative to adhesive bonding is to co-cure the joint. This process eliminates the adhesive layer and the two interfaces between the adhesive and the adherends. The continuous matrix surrounding the fibers on either side of the joint influences the load transfer and the corresponding stresses developed in the joint. In this study, finite element analysis was used to investigate the stresses developed in a co-cured stepped-lap joint made from adherends with unequal stiffness. Two different approaches were used to model asymmetric joints with uniform step lengths: a homogeneous approach that modeled each adherend as transversely isotropic, and a constituent-level approach that modeled the resin and idealized fibers individually. It was found that the co-cured stepped lap joint behaves very much like a series of adhesively bonded lap joints. The shear stress distribution for step length to ply thickness ratios greater than about 10 exhibits a parabolic shape with peaks at the ends and lower values in the center, which is very similar to the stress distribution in adhesively bonded stepped lap joints. It was observed that the peak and minimum stresses approach a steady value with increasing step length, implying that there may be a limiting strength for an asymmetric co-cured stepped lap joint.