The Damage Analysis Of Integral Stiffened Composite Panels Under In-plane Loads

As a kind of typical integration structure, the integral stiffened composite panels were widely used in various fields because of the excellent properties.Under the In-plane loads, composite laminate presented complex failure modes. Due to the deformation inconsistencies caused by the stiffness mismatch of rib and panel, the interface debonding can easily occur, resulting in failure ahead of time. Therefore, it is significative theoretically and valuable practically that studying the failure modes of integral stiffened composite panels and the influence of structural parameters on the bearing capacity.A strength analysis model was presented to study the progressive damage of integral stiffened composite panels subjected to in-plane loads by using the nonlinear finite element method. In the model, the debonding failure of the adhesive between skin and stiffener was considered by adding cohesive elements between the shell elements. Quads failure criteria and Hashin's failure criteria were adopted to identify the occurring of damage events of the cohesive elements and the composite panels, respectively. Based on ABAQUS, a material degradation rule containing continuum damage status variables was presented by user subroutine - umat. The process of damage initiation, propagation and catastrophic failure of three integral stiffened composite panels was simulated in detail by the proposed mode with the consideration of initial geometric imperfection. The results are well agreed with the experiment data, and can also explain the two different failure phenomena in the experiments.The in-plane axial stiffness ratio of stiffener and skin was introduced and conducted to study its effects on the carrying capacity and failure modes. For the T-stiffened plates, the effects of equivalent torsional rigidity, shearing rigidity, equivalent flexural rigidity and in-plane axial stiffness on the buckling load and ultimate strength were studied in detail under shear, combination of compression and shear loads. The results indicate that: in the context of the ply design is reasonable, increasing the stiffness ratio can to some extent improve the unit area bearing capacity of the cross section of stiffened composite panels; within certain limits, increasing the structure stiffness of stiffened plates can benefit the structure bearing capacity.