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цикла нагружения и переменной амплитуды, которая основывается на критерии
усталостного разрушения, определенном при постоянной амплитуде суммарной
удельной энергии упругой деформации. Относительная погрешность между
расчетными и экспериментальными данными не превышает 30,1%, а все расчетные
долговечности лежат внутри 2,5 прогнозируемого диапазона. Предложено
методологию ускоренного определения констант в модели усталостного разрушения,
основанную на критерии суммарной удельной энергии упругой деформации по
результатам испытания квазистатическим одноосным растяжением и при
фиксированной постоянной амплитуде нагружения.
Ключевые слова: псевдоупругий NiTi сплав, функциональная усталость,
конструкционная усталость, удельная энергия диссипации, суммарная удельная
энергия упругой деформации, водородное охрупчивание, асимметрия цикла нагрузки,
переменная амплитуда нагрузки, рост усталостной трещины, размах коэффициента
интенсивности напряжения, демпфирующие устройства, коэффициент потерь.
ABSTRACT
Iasnii V.P. Development of methods for predicting the fatigue life of pseudoelastic
shape memory alloys. Manuscript.
Thesis for the Doctor’s degree of Engineering Sciences in the specialty 01.02.04
Mechanics of deformable solid body. Karpenko Physico-Mechanical Institute of the
National Academy of Sciences of Ukraine, Lviv, 2021.
To solve an important scientific and technical problem, which consists in increase the
reliability of structural elements operation devices made of shape memory alloys, results
was formulated and substantiated. The results include fatigue failure criteria and methods
for predicting their durability, taking into account the influence of stress ratio and variable
amplitude loading.
The significant decrease in stress of austenitic-martensitic transformation σ AM (up to
14%) and the fracture stress (up to 24%) of the SMA NiTi alloy after electrolytic
hydrogenation compared to the material in virgin state was observed. Increasing the
intensity and duration of hydrogenation can lead to absence of plastic deformation region
on the stress-strain curve due to a combination of processes caused by hydrogenation of
intensive martensitic transformation and hydrogen embrittlement of martensitic structure.
There is a tendency to reorientation of the macrofracture surface from perpendicular, to the
axis of specimens, to the screw dislocation line, which is obviously due to the intensification
of martensitic transformation in the plane of maximum shear stresses.
The basic regularities of the influence of the parameters under variable amplitude
loading sequence with two blocks on the functional properties and structural fatigue of the
pseudoelastic SMA are established. Residual strain significantly increases with the increase
of loading cycles number at stress ratio R= 0,09 – 0,13 due to its proportional increasing
on the block I and reaches almost 7% before failure. The transition from high (I) to low (II)
block partially restores the functional properties of the NiTi alloy, the residual strain
decreases within the block II, which can be caused by a decrease in residual martensite. With
the increase of loading cycles’number, the dissipation energy increases at the start and end