Middle East Technical University Department of Metallurgical & Materials Engineering Thermo-Mechanical Fatigue and Fracture of Shape Memory Alloys Ceylan Hayrettin Ph.D. Student Materials Science and Engineering Department Texas A&M University, Texas, USA Shape memory alloys (SMAs) have the highest work output per unit volume among all active materials. This makes them ideal candidate for solid state actuators. There is a recent demand on aerospace, automotive and oil-gas industries for compact and powerful actuators. Fatigue and fracture of shape memory alloys have been studied primarily for superelastic region and just mechanically. In order to design SMA actuators, working condition od such devices must be mimicked for fatigue testing i.e. under constant stress thermal cycling tests until failure. Likewise crack growth will be different under pure mechanical conditions from thermo-mechanical ones. Several aspects of fatigue and fracture of SMAs will be presented. 10 4 Electrostrictive ceramics Actuation S tress (MP a) 10 Shape memory alloys 3 Magnetic shape memory alloys (Field induced phase transformation) Magnetostrictive materials 10 2 Magnetic shape memory alloys 100M J/m 3 (Field induced variant reorientation) 10 1 Electroactive polymers 10M J/m 3 Piezoelectric ceramics 10 0 1M J/m 3 10 -1 Shape memory polymers Piezoelectric polymers 10 100J /m 10J/m 3 -2 0.01 0.1 1 1K 3 10K J/m 3 J/m 3 10 100K J/m 3 100 A ctuation s train (% ) 5 Strain (%) 4 <100> 3 1000 nm 2 1 Strain in Marteniste Actuation Strain Strain in Austenite 0 0 400 800 1200 Number of cycles <010> <001> 1600 June 3rd 2015 (Wednesday) 13:00 @ MetE C-Aud. 100 nm