Research On Cohesive Zone Model Of Laminated Composites And Its Applications

It is important for detail design to research on damage analysis and failure evaluation of the jointinterfaces in integrated composite structures. At present, cohesive zone model (CZM) is one of themost effective methods for failure analysis of the joint interfaces. Several foundation problems existedin CZM have been studied in this paper. On this basis, the failure process of integrated compositestructures at the post-buckling stage is systematically discussed. The main features for this paper arestated as follows:(1) Two meso-mechanical models are presented to predict the strength parameter of CZM: onebased on the periodic RVE technique and the other based on Eshelbey’s equivalent inclusion method.The FEM simulations on mixed-mode-bending (MMB) test are presented by applying CZM with thepredicted cohesive strength. The numerical results are in fair agreement with experimentalobservation.(2) CZM of the stitch (or pin) is developed based the bridging law which can be derived from ameso-mechanical model of the stitch (or pin). Further more, zone dependent CZM is presented tosimulation both the delamination and the stitch (or Z-pin) failure in stitched composite structures. Thesimulations on MMB test of stitched laminates are done by the zone dependent CZM.(3) The mechanisms of the load transfer are analyzed on the stiffened composite panels subjectedto axial compressive load at the post-buckling stage. It is implied the initial failure is mostly to takeplace at nodal lines or anti-nodal lines. The failure mechanisms of the stiffened panels (includingstitched and unstitched panels) with or without initial damage induced by post-buckling are studiedvia CZM and progressive damage analysis based on Hashin failure criterion.(4) A six-point bending test is developed to characterize the failure process of the joint interfacein integrated composite structures induced by post-buckling. The deformation features at the nodaland anti-nodal lines at the post-buckling stage can be obtained from this test. Two failure criterions forthe interface de-bonding are proposed by the numerical research on the post-bucking induced failureprocess of the stiffened composite panels.(5) Three kinds of design schemes for the composite box are proposed according to the designrequirements. The analyses on the carrying capacity of these schemes at the post-buckling stage aredone by FEM. The experimental study is also carried out on one of these schemes (the top panel withmetal joints and the bottom panel with stitching). The simulation results of the breaking load and thefailure modes are in good agreement with the experimental ones. It validates the design and analysis methods proposed in this paper.