A protocol for characterizing the structural performance of metallic sandwich panels: application to pyramidal truss cores

All-metallic sandwich panels with truss and prismatic cores have impending application as ultra-light load bearing panels amenable to simultaneous active cooling and blast resistance. To facilitate application, a protocol for characterizing the structural performance of such panels is needed that can be used for design calculations. An approach capable of realizing this objective is presented and demonstrated for panels with pyramidal truss cores. It combines measurements, mechanism maps, finite element simulations and optimization. Mechanism maps based on beam theory are used to characterize face and core dimensions as well as to estimate minimum weight designs. Experimental measurements and finite element calculations are used to calibrate and understand the responses of the core in transverse compression, in-plane shear and stretch. Overlaying the measurements and simulations allows assessment of the mechanical properties of the core material, as affected by fabrication. The updated results are used to establish and calibrate an orthotropic constitutive law for the core. Bending tests performed on panels subject to two end constraints are used to assess the fidelity of the core constitutive law. The tests are simulated by using a stress/strain response for the faces obtained from independent tensile measurements. The comparison reveals that the loads are predicted quite accurately. However, when controlled by the core, the simulations predict a more abrupt yield point than that found experimentally.