Fracture Mechanics In the Presence of Reversible Martensitic Transformation in High Temperature Shape Memory Alloys

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The research objective of this award is a systematic experimental and theoretical investigation of the fracture response of nano-precipitation hardened high temperature shape memory alloys (HTSMAs) during actuation in the course of thermo-mechanically-induced reversible martensitic transformation. Affordable nano-precipitation hardened HTSMAs have extremely stable cyclic actuation response and can be used as high power output − an order of magnitude higher than any other actuator material available − solid state actuators in applications related to aeronautics, energy conversion and storage, consumer products, and automotive. Thermo-mechanical experiments will be performed on these materials to measure fracture toughness, investigate thermo-mechanically-induced crack growth, and identify the effect of shape, size and coherency of the precipitates on the fracture mechanisms. In parallel, the analytical efforts will be directed towards the understanding of the effect of thermo-mechanically-induced martensitic transformation on the mechanical fields near the crack tip, driving force for initiation of crack growth, and crack growth resistance.If successful, these studies would provide valuable information on the effects of shape memory performance metrics and micro-structural features to improve those metrics on the fracture behavior of HTSMAs. This information can eventually be used in their design and optimization, and permit their ultimate insertion into applications. The knowledge gained from these efforts will contribute to a new field of fracture mechanics that needs to be explored for global anisotropic phase transformation to be treated properly, and is expected to result in new theories for characterizing fatigue crack growth and lifetime in SMA actuators. The educational plan focuses on the development of teaching modules for incorporation into undergraduate and graduate courses on smart materials and fracture mechanics as well as on enriched international and industrial experiences for the students involved via the partnership with the NSF International Materials Institute (IIMEC) and the NSF - I/UCRC at Texas A&M University. Both initiatives will involve disseminating the knowledge generated through presentations, publications, the SMART website and the Consortium for the Advancement of SMA Research Technologies (CASMART).