The collapse response of sandwich beams with a Y-frame core subjected to distributed and local loading

Sandwich beams comprising a Y-frame core have been manufactured by assembling and brazing together pre-folded sheets made from AISI type 304 stainless steel. The collapse responses of the Y-frame core have been measured in out-of-plane compression, longitudinal shear and transverse shear; and the measurements have been compared with finite element predictions. Experiments and calculations both indicate that the compressive response is governed by bending of the constituent struts of the Y-frame and is sensitive to the choice of lateral boundary conditions: the energy absorption for a no-sliding boundary condition exceeds that for free-sliding. Under longitudinal shear, the leg of the Y-frame undergoes uniform shear prior to the onset of plastic buckling. Consequently, the longitudinal shear strength of the Y-frame much exceeds its compressive strength and transverse shear strength. Sandwich beams were also indented by a flat bottomed punch, and a relatively high indentation strength was observed. It is argued that this is due to the high longitudinal shear strength of the Y-frame. While finite element calculations capture the measurements to reasonable accuracy, a simple analytical model over-predicts the indentation strength. Finally, the finite element method was used to investigate the energy absorption capacity of the sandwich beams under indentation loading. The calculations reveal that for a given tensile failure strain of the face-sheet material, a sandwich beam with Y-frame core has a comparable performance to that of a sandwich beam with a metal foam core. The relative performance is, however, sensitive to the choice of design parameter: when the indentation depth is taken as the design constraint, the sandwich beam with a Y-frame core outperforms the sandwich beam with the metal foam core.