Parametric investigation of mechanical properties of auxhex unit cell sandwich structures

Abstract

In this study, the mechanical properties of the AuxHex structure, which consists of hybrid unit cells obtained by combining the classical hexagonal honeycomb unit cell structure with the auxetic unit cell structure, are investigated under axial compressive loads by changing the geometric parameters. In the studies carried out, it has been observed that the AuxHex structure, which is obtained by hybridizing two different cell structures, has a better strength value against in-plane compressive loads. Before investigating the effect of geometric parameters on the mechanical properties of the AuxHex structure, a validation study was performed by analyzing the AuxHex structure using the ABAQUS 2020 commercial finite element program with an appropriate study in the literature and based on the results of this validation study, the boundary and loading conditions, material properties to be defined, and other variables for finite element models and analyses of other AuxHex structures have been determined. Subsequently, the mechanical properties, including Young's modulus, yield strength, energy absorption capacity under different strain values, and toughness were investigated for nine (9) different geometries of AuxHex sandwich structures by varying geometric parameters such as inclined and non-inclined wall cell lengths, angles, and wall thicknesses that characterize the AuxHex unit cell structure. To analyze the Young's modulus and yield strength among these mechanical properties, both theoretical formulas used in the literature and finite element analysis results were utilized. The results obtained from the finite element analyses were employed to determine and compare the absorbed energy under certain strains and toughness values of nine (9) different AuxHex structures. The force-displacement graphs obtained from the finite element analyses were converted into stress-strain graphs. The resulting stress-strain graphs were integrated by using a curve fitting function in the MATLAB program to obtain the absorbed energies and toughness values at different strains values. These graphs were also useful for determining the Young's modulus and strengths. As a result of all these studies, it was observed that the elastic modulus, yield strength, energy absorption capacity, and toughness of the sandwich structure decreased with increasing inclined and non-inclined wall lengths of AuxHex unit cells. However, it was concluded that all these mechanical properties increased significantly and had a positive effect on the structure with increasing AuxHex unit cell wall thicknesses. Finally, it was concluded that the elastic modulus, yield strength, energy absorption capacity, and toughness of the AuxHex sandwich structure decreased with increasing angle values used to design the AuxHex unit cells, and lastly, the combination of all AuxHex structures' stress-strain graphs in one shows that the collapse behaviour of structure appears to be largely related to the change in the length of non-inclined wall.