Analysis of thermally induced stresses on the core node bonds of a co-cured sandwich panel

During process development testing of the ARES I composite interstage, large regions of node disbonds were observed in the aluminum honeycomb core. The sandwich panels were composed of carbon fiber/epoxy face sheets and one-eighth inch cell size aluminum core co-cured in an autoclave. Node disbonds were initially observed after cure with ultrasonic inspection and subsequently confirmed with X-ray inspection and cross sectioning. A stress analysis was performed on the residual thermal stresses resulting from post-cure cool down. Analysis indicated that the thermal stresses in the aluminum core are a function of foil thickness of the aluminum core. Thermal stresses are relieved through disbonding of the adhesive node. The node disbonds were shown to significantly reduce the shear capability of the sandwich structure. Funding was provided by the ARES I Upper Stage Project.