Shape memory alloy honeycombs: experiments & simulation

Metallic foams and honeycombs, with their light-weight, high speciflc stifiness, and well-developed energy absorption characteristics, are of obvious utility in engineering applications. However, these structures, often made of aluminum, sufier permanent deformation after crushing. Cellular structures made from shape-memory alloys (SMAs) are particularly intriguing for their potential to deliver shape memory and/or superelasticity in a light-weight material. Realization of open-celled Nitinol has recently become possible via a (newly discovered by Profs. D. Grummon at Michigan State Univ. and J. Shaw at Univ. of Michigan) transient-liquid reactive brazing system for creating robust metallurgical Nitinol-Nitinol bonds. With this technique, prototype sparse cellular honeycomb structures have been made and tested, showing up to 50% repeatedly recoverable strains. Two difierent microgeometry NiTi honeycombs have been tested, a hexagonal for isothermal conditions and a corrugated for thermal cycling. Moreover, the isothermal experiments are simulated using a model that accounts for flnite rotations and hysteretic responce of the ligaments and geometric imperfections of the flnite size samples.