Delamination and debonding failure of laminated composite T-joints

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Composites are increasingly being used in aerospace, automotive and other industries. The T-joint (also named stringer stiffened skin) is a typical connection, broadly used in thin-walled structures, such as the wing and fuselage of aircraft. This thesis presents the analysis of the delamination and debonding failure of laminated composite T-joints, in support of the design and manufacture of integrated composite structures. Major attention has been paid to expand current knowledge on the failure response of the subcomponents of the T-joints: the through thickness reinforcements and adhesive layers were investigated both numerically and experimentally. Novel experimental methods and computational models have been developed to facilitate the characterization of these subcomponents and the in-depth understanding of the failure mechanisms of these subcomponents. The cohesive zone model has been used widely for modeling various fracture problems of the investigated materials. Novel cohesive laws were developed to represent the complex constitutive responses of these materials, and different mesh distribution strategies were employed as well. Pull-off and bending tests of T-joints were carried out where the failure process and loading capacity were evaluated. On the basis of the knowledge and analysis methods accumulated from the subcomponent studies, the delamination and debonding failure of T-joints has been numerically modeled; comparisons with experimental results have validated the accuracy and reliability of these numerical models. It is believed that this thesis has contributed to better understanding of the delamination and debonding failure of composite T-joints; the knowledge, methods and philosophy outlined here may also be applied to other composite/adhesively bonded structures as well.