Gollerthan, S.; Young, M. L.; Baruj, A.; Frenzel, J.; Schmahl, Wolfgang W.; Eggeler, Gunther
Fracture mechanics and microstructure in NiTi shape memory alloys.
In: Acta Materialia, Vol. 57, No. 4: pp. 1015-1025
Full text not available from 'Open Access LMU'.
Crack extension tinder static loading in pseudoplastic and pseudoelasticbinary NiTi shape memory alloy (SMA) compact tension (CT) specimens wasexamined. Two material compositions of 50.3 at.\%, Ni(martensitic/pseudoplastic) and 50.7 at.\%, Ni(austenitic/pseudoelastic) were investigated. The SMAs werecharacterized using differential scanning calorimetry to identify thephase transformation temperatures and tensile testing to characterizethe stress-strain behavior. A miniature CT specimen was developed, whichyields reliable critical fracture mechanics parameters. At 295 K, crackspropagate at similar stress intensities of 30 +/- 5 MPa root m intomartensite and pseudoelastic austenite. Integrating the miniature CTspecimen into a small test device which call be fitted into a scanningelectron microscope shows that this is due to cracks propagating intoregions of detwinned martensite in both materials. Investigating apseudoelastic miniature CT specimen in a synchrotron beam proves thatmartensite forms in front of the crack in the center of the CT specimen.i.e. under plane strain conditions.