Basic two-dimensional core types for sandwich structures

The mechanical characteristics of three types of core with two-dimensional isotropic patterns – triangular, hexagonal, and starcell – were studied as related to applications in sandwich structures. The Youngʹs modulus, shear modulus, and Poissonʹs ratio were calculated for the three core types in the direction normal to the faces. The compressive buckling strength and shear buckling strength were calculated for the three core types by modeling each cell wall of the core as a plate under compressive or shear load. To verify this model, tests were conducted on scaled specimens to measure the compressive buckling strength of each core. The bending flexibilities of the three cores were also studied. Compliances for the three cores were measured using biaxial flexural tests. Tests were performed on each core type in which the deflection of a circular core sample loaded at its center was measured. The three isotropic core patterns exhibited distinct characteristics. In the direction normal to the faces, all three cores had the same stiffness. However, the triangular core had lower compressive and shear buckling strengths than the other two core types. The starcell core exhibited high flexibility compared to the other cores, indicating a potential for application in curved sandwich structures.