Tensile failure mechanism of RTM-made asymmetric composite T-joint

The tensile tests of structural symmetric and asymmetric composite T-joints prepared by resin transfer moulding (RTM) process were carried out, respectively. The failure process, structure stiffness and failure load of these composite T-joints were compared and analyzed. At the same time, the cohesive zone models (CZM) of composite T-joints were established and the failure process and failure mechanism of these two type T-joints were studied. The interlaminar stress of T-joints with different deflection angles were also compared. The test results show that the failure mode of structural asymmetric T-joint is different from that of symmetric T-joint. The existence of deflection angle causes higher stress at the large angle curved web than that of the small angle curved web, as a result, the initial crack of asymmetric T-joints orientationally occurs at the interface of triangular zone/curved web with large deflection angle. And then the crack directly propagates to the interface of large deflection angle flange/skin with 15.3% higher peak failure load than that of symmetric T-joints. The small bending deformation of the skin of asymmetric T-joint leads to the larger overall stiffness of the structure. The debonding of flange and skin is the prominent reason to the final failure of T-joint. The finite element analysis results show that the simulated peak failure loads of symmetric and asymmetric T-joints are within deviation. The simulated failure mode is in good agreement with the experiment. As the deflection angle increases, the interlaminar stress at the curved web of asymmetric T-joint decreases gradually, which indicates that the initial failure load of asymmetric T-joint may increase correspondingly. The position of initial crack will be shifted to the end of curved web at the same time.