Numerical and experimental analysis of a triangular auxetic core made of CFR-PEEK using the Directionally Reinforced Integrated Single-yarn (DIRIS) architecture

The Directionally Reinforced Integrated Single-yarn (DIRIS) architecture is a novel, patented concept of creating directionally reinforced high-strength cores for sandwich panels developed at the Institute of Mechanics of Materials and Geostructures S.A. This technology using glass or carbon fibre-reinforced PEEK has been so far implemented on high-strength honeycomb cores of triangular isogrid geometry with impressive results in all constitutive parameters both in-plane and out-of-plane. In this paper the application of the DIRIS technology on creating high-strength auxetic triangular cores is presented. The mechanical behaviour of the resulting core and panel was numerically investigated using FEA and testing on manufactured prototypes confirmed the high strength of the proposed design. In fact the shear modulus of the DIRIS auxetic cores was found superior to that of existing mass-produced honeycomb cores despite the inherent complexity of the geometrical configuration and the non-standardized manufacturing method.