Evaluation of an analytical approach predicting the transversal failure load of insert connections in sandwich structures

Kurzfassung

The main objective of this work is to develop an analytical tool to predict failure loads of separable insert joints of sandwich structures. Insert connections provide several bonding interfaces to the honeycomb core as well as to the skin sheets, varying in number, position and size depending on the insert type. The idea is to improve these load paths on their quantity, quality and transferring load portions. With this paper the current status of this investigation is provided. Through-the-thickness insert connections are selected for experimental benchmark testing due to their high load-to-weight ratio. The first failure mode under transversal loads is shear buckling of the honeycomb core cell walls. This failure type is evaluated by a convenient applicable, semi-analytical equation, recommended by ECSS [1]. This formula is based on the “simple sandwich theory”, considering the design parameters core and skin sheet thickness, core shear strength, honeycomb cell size and insert radius in linear dependence. In contrast, the face sheet flexure stiffness as well as core density is not considered within the analytic equation, though their influence is not negligible. If significant tendencies of these non-considered parameters are deductible, the analytical approach could be extended. Therefore, analytical predictions are compared to benchmark test data taken from several sources. The analytical predictions show sufficient correspondence to the test data results, confirming the assumption of a linear dependency of the considered design parameters.