On the influence of overlap topology on tensile strength of composite bonded joints

Abstract

The goal of this study is to investigate new designs of composite bonded joints in order to improve their strength under tensile loading. Multiple stacked overlaps are compared with single overlap designs. The concept of multiple stacking is well known as ply-interleaving technique for co-curing dissimilar materials. For a secondary bonding process, a similar concept is used in tongue-and-groove joints. However, it is so far limited to one stacking level due to the complexity of the design. By means of thin unidirectional layers, the tongue-and-groove design is expanded further to two stacking sequences and applied to secondary bonding of CFRP adherends. Single lap joints of 12.7 and 25.4 mm overlap length were compared to finger joints with 1 and 2 overlaps of 12.7 mm overlap length, stacked through the thickness. Specimens were tested according to ASTM D-5868-01. The initial and final failure load were recorded. The study shows that for the same overlap length in a multi-stacked configuration, there is a potential for higher average lap strength, in comparison with an increase in overlap length of a single overlap. This effect might be mainly due to the reduction of secondary bending moment and by load distribution over multiple interfaces.