Modified Metallic Octet Truss Cellular Cores for Sandwich Structures Fabricated by an Expanded Metal Forming Process

Abstract

A new idea for fabricating a truss periodic cellular metal (PCM) is described. Namely, an octet-like truss PCM named ‘M-octet’ is fabricated by folding expanded metals. Its strengths under compression and shear load estimated by elementary mechanics are compared with experimental results and those of other competing cellular metals. When employed as a core in a sandwich panel, the load capacity subjected to bending load is predicted by an energy-based approach for various failure modes. For a given core height, a failure mode map is constructed with the nondimensional parameters such as geometric variables, material parameter (yield strain), load index, and weight index. Based on the failure mode map, three designs are chosen for maximum load per weight ratio. The predicted failure loads for the three different geometric designs are compared with the values measured through the experiments which are performed with sandwich specimens with the tetrahedral truss cores made of a wrought steel SS41. The measured equivalent normal yield and shear yield stresses agree fairly well with those predicted by the analytic solutions. In the three-point bending tests, the design with the thickest core truss and face sheets shows the peak load point delayed the most, which gives benefits in terms of the energy absorption and deformation stability after the peak load point.