Bending behavior of lightweight sandwich-walled shells with pyramidal truss cores

A study on the bending response of a composite curved panel with pyramidal metallic truss cores suitable for functional applications is presented using a combination of analytical modeling, three-point bending experiments and finite element (FE) based simulations. The aluminum pyramidal cores were constructed using an interlocking method before curing with composite face sheets to fabricate the final structure. A theoretical model was developed to analyze the experiments and develop failure criteria. Three failure modes: (i) face wrinkling, (ii) face crushing, and (iii) debonding between face sheet and truss cores, were considered and theoretical relationships for predicting the collapse load associated with each mode were developed. The experiments were carried out on two sets of specimens with differing face sheet thickness which clearly indicated the important role played by core debonding in determining the peak load of the structure. Localized buckling instabilities were also reported for samples with thinner face sheets. The role of debonding in determining strength was further highlighted by a comparison with FE simulations with suppressed debonding. Curved panels with sandwich construction are used successfully in a variety of applications such as spacecraft, aircraft, train/ car, and boat/ship structures. However, traditional sandwich shells made from foam [1,2], corrugated [3,4] and honeycomb cores [5] with close-cells cannot accommodate free fluid movement through them. This limit on flow circulation imposes significant restrictions in thermal and transport properties preventing their deployment as functional structures. Therefore, fabrication of sandwich panels with open-cell core constructions with interconnected void spaces can extend the usage of sandwich panels to functional applications [6]. To this end, metallic truss cores have generated interest as alternatives to honeycombs when used as core constructions of sandwich panels designed to support quasi-static [7–9], dynamic [10–15] or thermal loads [16]. Such fiber reinforced composite sandwich panels with lattice core construction are already of increasing interest in aerospace and marine applications. The effort to fabricate low density lattice core construction has been considerably accelerated by the utilization of several manufacturing techniques including Kirigami techniques [17,18], interlocking [19], hot press molding [20,21], laser cutting [22], pultruded unidi-rectional fiber-reinforced composite rods without helical forming [23] and water-jet cutting [24]. Significant amount of literatures exist about the bending behavior of flat sandwich panels with lattice cores. Xue et al. [25] and Vaziri and Xue [26] proposed a general homogenization method for modeling the response of low density core constructions capable of simulating the response of …