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HCF‐Umlaufbiegeermüdung von pseudoelastischen NiTi‐Formgedächtnislegierungen
Author(s) -
Rahim M.,
Frenzel J.,
Frotscher M.,
Heuwer B.,
Hiebeler J.,
Eggeler G.
Publication year - 2013
Publication title -
materialwissenschaft und werkstofftechnik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.285
H-Index - 38
eISSN - 1521-4052
pISSN - 0933-5137
DOI - 10.1002/mawe.201300118
Subject(s) - nickel titanium , materials science , bending , rotation (mathematics) , martensite , shape memory alloy , pseudoelasticity , structural engineering , tension (geology) , cyclic stress , compression (physics) , composite material , engineering , microstructure , mathematics , geometry
In the present work, a computer‐controlled test rig for simultaneous fatigue testing of several pseudoelastic NiTi wires through bending rotation is described. Bending rotation fatigue (BRF) testing represents a displacement‐controlled experiment where a straight wire is bent into a semi‐circle und forced to rotate around its axis. Thus, each point on the wire surface is subjected to alternating tension and compression. A test rig, which allows to control loading amplitudes, rotation frequencies and temperatures is described. We report preliminary results of an experimental program, which aims for a better understanding of fatigue lives, crack initiation, and crack growth in pseudoelastic NiTi wires. It was found that a good surface quality is of utmost importance to avoid early crack initiation. Wöhler curves of pseudoelastic NiTi wires typically show two different regimes depending on the maximum imposed surface strain during bending rotation fatigue testing. Larger strain amplitudes, which are associated with macroscopic formation of stress‐induced martensite, result in relatively low fatigue lives (LCF regime). In contrast, cycle numbers exceeding 10 7 were obtained for strain amplitudes where no large scale stress‐induced formation of martensite occurred (HCF regime).