Numerical investigation of compact-tension specimen failure based on auxetic structures

The study of crack growth behavior and fracture mechanisms in engineering materials plays a pivotal role in enhancing the design of resilient structures and in the development of advanced materials. In this context, auxetic structures, characterized by a negative Poisson's ratio, have introduced new perspectives in the field of fracture mechanics due to their unique properties. The present work numerically investigates the fracture behavior of a compact-tension (CT) specimen with a pre-crack and standard geometric dimensions, based on auxetic cellular structures fabricated from 7075-T651 Aluminum Alloy. The objective is to evaluate crack propagation, reaction forces and energy absorption in various lattice structures with negative and positive Poisson’s ratios. For this purpose, the specimen geometries were designed by embedding unit cell patterns within the rectangular region of the specimen while maintaining the uniform thickness of the surrounding cell walls. Uniaxial tensile loading was then simulated using pre-designed grips. Furthermore, a uniaxial tensile test simulation was conducted for all specimens in accordance with relevant standards to determine and compare their Poisson's ratios. To facilitate a mass-independent comparison of structural performance, the reaction forces were normalized. Analysis of the results indicates that the auxetic structures developed in this study exhibit a significant improvement in fracture resistance over the conventional re-entrant auxetic structure.