An Investigation of the Enhanced Fatigue Performance of Low-porosity Auxetic Metamaterials

An experimental and numerical investigation of fatigue life and crack propagation in two-dimensional perforated aluminum structures is presented. Specifically, the performance of positive Poisson's ratio (PPR) geometries using circular holes is compared to that of auxetic stop-hole and straight-groove hole geometries. Mechanical fatigue testing shows that the considered auxetic structures have more than 20% longer life than the porous PPR structure at the same porosity and peak effective maximum stress despite having holes with larger stress concentrations. Digital image correlation is used to detect crack initiation and damage propagation much earlier than can be detected by the unaided eye. Accompanying finite element analyses reveal that auxetic structures have the advantage over their PPR counterparts by delaying crack initiation, spreading damage over a larger area, and having a stress intensity factor that decreases over a significant range of crack lengths. In addition, numerical simulations suggest that auxetic structures maintain their negative Poisson's ratios in the presence of cracks.