Simulations and Optimisation of Functionally Graded Auxetic Structures

Auxetic structures exhibit negative Poisson’s ratio and offer some enhanced properties in density, stiffness, fracture toughness, energy absorption and damping. This work presents analysis of auxetic structures fabricated from the Ti-6Al-4V powder by using the selective electron-beam melting (SEBM) at the Institute of Materials Science and Technology (WTM), University of Erlangen-Nürnberg, Germany. Quasi-static compressive testing of auxetic specimens in two different directions was performed to determine their basic mechanical behaviour. The results from experimental testing were used to validate developed discrete computational models built with the beam finite elements as well as homogenised computational models by using the crushable foam material model. The difference in post yielding behaviour between material models MAT_024 and MAT_153 in LS-Dyna was investigated. Validated discrete computational models were used for further optimisation of auxetic structure geometry to obtain user defined response during compression loading by applying functionally graded porosity. The optimised geometries of new auxetic lattice structures with functionally graded porosity were developed by using the Ls-Opt.