Bending response and failure mechanisms of composite sandwich panels with different cruciform stiffener configurations

Cruciform stiffener intersections connect orthogonal load paths in composite sandwich decks, but their construction details can introduce competing failure mechanisms. Three-point bending tests and progressive-damage simulations were used to compare two complete manufacturing configurations, with three specimens tested for each. Configuration C used integral CFRP wrapping, whereas configuration D combined interrupted longitudinal stiffeners, interleaved ply overlaps and a secondary overlaminate. The sample mean peak loads were 57.30 kN for C and 66.86 kN for D, while the peak-load coefficient of variation increased from 7.22% to 14.38%. Their loading-interval stiffnesses were comparable. The observed failures differed: C developed a transverse fracture band in the wrapping laminate at the stiffener base, whereas D exhibited separation along the overlaminate side-wall connections. The simulations associated the major load drops with local tensile failure of the wrapping laminate in C and expanding interface degradation in D. Peak loads were reproduced more closely than peak displacements and post-peak responses; the predicted damage sequences therefore provide qualitative interpretations of the observed failures. These results identify different critical regions for the two connection constructions under quasi-static bending.