Experimental Validation of a Residual Stress Hypothesis for Bond Lines in Thick Adhesive Joints

In this work a novel approach for the prediction of cure-induced residual stresses in bond lines of wind turbine blades is validated through an experimental campaign at coupon level. The adhesive strength of the neat material is compared to the adhesive structural strength of a bonded joint. Bonded sandwich and neat adhesive specimens are manufactured under identical boundary conditions. A residual stress hypothesis for the cure-induced residual stress state in the sandwich specimens is raised, considering the manufacturing conditions. The specimen sets are subjected both to static and tension-tension fatigue loads. The sandwich specimens are tested with a load ratio of R=0.1, where the neat adhesive specimens are loaded with the load case resulting from an R=0.1 load ratio with amplified mean stresses, equal to the predicted residual stress state of the adhesive in the sandwich laminate. The results are analyzed statistically and found to be in a good agreement.