Damage tolerance of low-velocity-impacted composite sandwich structures

This study is focused on the damage tolerance of composite sandwich structures at the low velocity impact damage level. The ultimate purpose of this research is to fill the current technical gap that there is lack of feasible methodology in the damage tolerant design of the composite sandwich structures and the safety evaluation of impact damaged composite sandwich structures.; Based upon Sandwich Compression After Impact (SCAI) tests, a nonlinear finite element model and a modified analytical model were developed and implemented in this study to investigate the damage propagation behavior of an impact damaged composite sandwich panel under in-plane uniaxial compression. In the nonlinear finite element model, due to the symmetry, one quarter of the whole sandwich panel was modeled in ANSYS with corresponding major impact damage modes. A program was coded to control the solving process with the incorporation of the consequential core crushing mechanism by using element deactivation technique. In the analytical model, the impacted facesheet was modeled as an angle-ply composite laminate, which has an initial deflection in shape and is partially supported by an elastic foundation, residing in a compressive stress field. Two coupled Partial Differential Equations (PDEs) were derived and solved numerically. A consequential core crushing mechanism was included in the solving process. Both numerical models successfully captured the damage propagation behavior similar to that in SCAI tests; especially, for the first time, successfully captured the initiation of damage propagation at the points near the damage zone with a good correlation to the experimental results.; An even driven failure criterion called Damage Propagation Criterion was proposed by using the critical far field stress corresponding to the initiation of damage propagation near the damage zone as the only characteristic value. With the implementation of this criterion, a feasible methodology was proposed for the engineering applications in the damage tolerant design of composite sandwich structures and the safety evaluation of low velocity impacted composite sandwich structures.