M. L. Young, S. Gollerthan, C. Somsen, Ruhr University, Bochum, Germany; J. Frenzel, Ruhr University Bochum, Bochum, Germany; G. Eggeler, Ruhr-University Bochum, Bochum, Germany
Binary NiTi shape memory alloy (SMA) was examined in three states (austenitic, pseudoelastic, and martensitic). Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Tensile testing was performed to characterize the stress-strain behavior. Crack loading and crack extension of these NiTi SMA miniature compact tension (CT) specimens were examined during static loading to yield reliable critical fracture mechanics parameters for all three states. High-energy synchrotron X-ray diffraction was used to identify phase volume fractions, textures, and lattice strains near the crack tip of a pseudoelastic CT specimen. Infrared (IR) thermography during in-situ, dynamic loading and unloading was performed to observe heat effects associated with the stress-induced transformation of martensite from B2 to B19’ during loading and the reverse transformation during unloading of a pseudoelastic NiTi SMA. The microstructures of all three states are discussed in view of the crack growth mechanisms.
Summary: Binary NiTi shape memory alloy (SMA) was examined in three states (austenitic, pseudoelastic, and martensitic). Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Tensile testing was performed to characterize the stress-strain behavior. Crack loading and crack extension of these NiTi SMA miniature compact tension (CT) specimens were examined during static loading to yield reliable critical fracture mechanics parameters for all three states. High-energy synchrotron X-ray diffraction was used to identify phase volume fractions, textures, and lattice strains near the crack tip of a pseudoelastic CT specimen. Infrared (IR) thermography during in-situ, dynamic loading and unloading was performed to observe heat effects associated with the stress-induced transformation of martensite from B2 to B19’ during loading and the reverse transformation during unloading of a pseudoelastic NiTi SMA. The microstructures of all three states are discussed in view of the crack growth mechanisms.
