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ABSTRACT
Iasnii V.P. Development of pseudoelastic shape memory alloys lifetime
prediction methods. Manuscript.
Thesis for the Engineering Sciences Doctor degree on the specialty 01.02.04
Mechanics of Solid Deformable Body. Karpenko Physico-Mechanical Institute of
the National Academy of Sciences of Ukraine, Lviv, 2021.
In the thesis, there was solved the important scientific and technical task, aimed
at the increase of devices reliability, that contain shape memory alloys elements,
сonsidering the criteria of their fatigue fracture and methods, that allows to predict their
lifetime taking into account the influence of stress ratio and variable amplitude loading.
There was proposed a number of methods that allow studying the influence of
temperature in the range, close to climatic, as well as the material behavior after the
hydrogenation, the stress ratio and variable load amplitude on strength, fracture
toughness, functional properties and structural fatigue of shape memory alloys using
load-, strain- and energy-based parameters.
There was found the significant decrease of the initiation stress for forward
transformation into martensite, σ Ms by 14% and the failure stress by 54% of the
hydrogenated alloy in comparison with non-hydrogenated. By increasing the intensity
of hydrogenation and its duration, it is possible to omit the plastic deformation region
on the stress strain curve of the specimen by combining the processes caused by
intensive martensitic transformation hydrogenation and hydrogen brittleness of
martensitic structure. It was found, that there is a reorientation tendency of the
macrofracture surface from perpendicular to the axis of the specimen to the fracture
along the helix, which is obviously due to the manifestation of factors enhancing the
martensitic transformation in the plane of maximum shear stresses.
The main regularities of the influence of stress range, temperature, stress ratio
on the functional properties and structural low-cycle fatigue of the pseudoelastic NiTi
alloy were studied. It was found that the dissipation energy and the loss factor on
stabilisation area are invariant to the number of cycles and stress range, which does not
