A Semi-Analytical Approach for Predicting the Stresses and Failure Modes of Composite Lugs

Abstract

Lugs are a specific type of joint with a semi-circular geometry around the pinhole utilized in the aerospace field. Its distinct geometry and ability to carry loads in its plane make it a very common choice for design engineers. Although this type of joint is widely used, there are no analytical equations that can predict the stresses around the hole. This research topic presents a semi-analytical approach to predict the in-plane stresses and failure modes of a composite lug under tensile pin loading. The methodology developed is based on stress functions for anisotropic beams implemented in stress equations for solid bodies in a polar coordinate system. The results of this approach are validated with the use of numerical simulation models, whose trustworthiness is verified by tensile tests. The outcome of this thesis is in-plane stress distribution graphs for every layer of the laminate around the hole and the in-plane failure mode of the lug. The results show a good accordance between the stresses predicted from the semi-analytical approach and the numerical simulations. Moreover, two lug designs with different geometric characteristics were tested in order to observe the influence of the geometry on the failure load. It was concluded that the geometry affects the maximum failure load but not the stress distribution, which is concurrent with the literature. Overall, the methodology presented in this research topic provided promising results. The findings of this thesis can have a great impact and aid engineers in estimating the stresses in a composite lug from the preliminary phase of a project.