Research On The Interfacial Reinforcement Design Of Composite T-joints

Composite T-joint is a typical form of structure widely used in modern aircrafts. Delamination between the skin and flange is the typical failure mode of T-joints. Z-pin can significantly increase the interfacial performance between skin and flange. The finite element model is created for the Z-pin reinforced composite T-joint by using the commercial software ABAQUS, and the effects of Z-pin on the performance composite T-joints are studied in this paper. The main contents of this paper are summarized as below:1. The cohesive behavior based on cohesive zone model(CZM) is introduced. The quadratic traction criterion is used to predict the initiation failure of cohesive behavior and the mixed-mode power law energy release rate criterion is used to predict the spread of failure of cohesive behavior.2. The three dimensional finite element model is created for the composite T-joint under tensional load. Cohesive behavior is defined to simulate the delamination of interface. The nonlinear spring elements combining with the micromechanical approach are used to simulate the effects of Z-pin. The finite result are in good well with the test results. The method of cohesive behavior simulating the delamination of interface as well as the nonlinear spring element simulating the effects of Z-pin are proved to be reliable. Then the two dimensional finite element model is created for the composite T-joint under tensional load, cohesive behavior is also defined to simulate the delamination of interface. The nonlinear spring elements combining with the micromechanical approach are also used to simulate the effects of Z-pin. The finite result are in good well with the test results, thus getting ready for the parametric analysis of Z-pin.3. The three dimensional finite element model is created for the composite T-joint under bending load. A ufield subroutine defining three dimensional Hashin criterion is referenced to build the stiffness degradation model. The effects of material damage of composite T-joint on the carrying capacity of T-joint under bending load is studied. Z-pin reinforcement of the flange region can rarely increase the carrying capacity of composite T-joint under bending load.4. The two dimensional finite element models are used to analysis the effects of parameters of Z-pin on the carrying capacity of composite T-joints under tensional load. The effects of the location of Z-pin are deeply researched also. Several suggestions are proposed for the design of Z-pin reinforcement.