Effect of secondary bending on strength prediction of composite, single shear lap joints

The influence of secondary bending on strength prediction of composite joints has been studied by means of detailed finite element analyses. Secondary bending was changed in magnitude by altering the length of the overlap region, in a two-fastener specimen, while leaving all other joint parameters unchanged. It was found that secondary bending influences the various macroscopic failure modes, and thus has the potential to change the mode of failure and affect the ultimate failure load. Under tensile loading, secondary bending increased the contact area between the fasteners and the hole edges which reduced the bearing stresses and increased the bearing strength. Secondary bending also increased the bending of the plates and thus generated more severe net-tensile stresses which resulted in reduced net-tensile strength. Under compressive loading, secondary bending reduced the net-compressive strength due to the increased plate bending. The effect of secondary bending on bearing strength is difficult to predict and must be evaluated on an individual basis. It was concluded that secondary bending needs to be accounted for in accurate strength predictions.