Simulations of Mechanical Response of Superelastic NiTi Helical Spring and its Relation to Fatigue Resistance
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Behavior of NiTi shape memory alloys under complex loading is still a subject of both experimental and theoretical investigations. One of the simplest geometries, in which the material is loaded in combined mode and which has also several practical applications, is a simple helical spring. In this contribution, mechanical response of NiTi superelastic spring is analyzed in detail by numerical simulation and the results are compared to experiments. The simulations show complex stress state, which develops during spring stretching. Analyzing fatigue tests with respect to simulated behavior allowed us to find relation between fatigue resistance and periodic changes in volume fraction of martensite induced by cyclic mechanical loading. The work also underlines an extension of the range of stroke amplitudes guaranteeing enhanced life performance of the spring when material transforms through the R-phase.
Keywordshelical spring non-proportional loading numerical modeling R-phase shape memory alloys
We would like to thank to prof. T. Ben Zineb for providing access to CLCM computation cluster (Centre Lorrain de calcul haute performance en mécanique, France). This work has been conducted within the institutional project RVO: 61388998 of IT ASCR, v.v.i., and within the CENTEM project CZ.1.05/2.1.00/03.0088. The research has also been supported by the Grant Agency of the Czech Republic through grant projects Nos. 13-13616S, 14-28306P, and 14-15264S and by Academy of Sciences through internal project No. M100761203.
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