| As a typical structure in aeronautics engineering, stiffened composites considerably increasestructural stiffness, strength with less weight and simultaneously enhance the load-carrying capacityof panel and integrated structure. However, due to the prevailing disadvantage of lowimpact-resistance of composite structure, damages such as fiber fracture, matrix cracking, matrixcrushing, delamination and so on can be effortlessly caused under the impact, especially low-velocityimpact, from external mass. These damages extensively distribute within the internal zone ofstructures and cannot be visually investigated easily, which reduces to a large extent the structuralload-bearing capability and in-serve lifetime and extremely threaten the safety of aircraft structures.Therefore, it has become especially significant for aeronautical application of stiffened compositepanels to uncover the low-velocity-impacted damage issue of stiffened composites.A progressive damage finite element model was established for the analysis of stiffenedcomposite panels under transversely low velocity impact by3-D dynamic finite element method. Fivetypical damage modes including fiber tensile failure, matrix crushing and delamination wereconsidered in the model. Strain-based Hashin failure criteria coupled with corresponding stiffnessdegradation schemes was used to predict the type and evolution of intralaminar damage modes byVUMAT user-defined subroutine. Cohesive elements were adopted in interlaminar zones and zonesbetween stiffener and laminates to simulate the initiation and evolution of delamination throughstress-based failure criteria and facture-mechanics-based energy criterion. The reasonability andeffectiveness were validated by the comparison between numerical simulation results andexperimental data. Finally, the influence of impact position, impact energy and initial damage(delamination) on the low-velocity impact damage of stiffened composite panels was discussed indetail. |
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