Page 10 - УДК

10

failure criterion (total elastic energy density). There was confirmed by fractography the

same type of quasi-chipping (spalling) mechanism of specimen failure due to the

transformation of austenite into martensite in the pre-failure zone of deformation.

A method for predicting the residual lifetime of cylindrical SMA elements with

a semieliptical surface crack was proposed. The method is based on solving the system

of equations that describe crack propagation, load parameters and cyclic crack growth

resistance taking into account their statistical scatter and changing the crack front shape

during propagation.

There was developed the damping device based on pseudoelastic SMA,

protected by patents. There was proposed a method for calculating damping device

strength, structural and technical parameters.

Scientific novelty of obtained results

1. There was proposed a number of methods for studying the functional

properties and structural fatigue of shape memory alloys using load-, strain- and

energy-based approaches taking into account temperature, hydrogenation, stress ratio

and variable amplitude.

2. There was found the effect of a significant decrease in the initiation stress for

forward transformation into martensite and failure stress of the hydrogenated alloy in

comparison with non-hydrogenated, as hydrogen affects the phase transformation

process and promotes brittle stratification along the plates of martensitic crystals.

3. There was obtained a set of new experimental data on the change of fatigue

lifetime, cyclic crack growth resistance and functional properties of NiTi alloy

depending on the temperature and stress ratio under constant and variable amplitude

loading.

4. For the first time, there was revealed the effect of partial recovery of functional

properties of nitinol alloy under variable amplitude loading sequence with two blocks

and the mechanism is proposed. This effect occurs at block with low amplitude and

leads to reduction of residual strain that could be the result of residual stresses decrease.

5. There was proposed the criterion of low-cycle fatigue failure of pseudoelastic