This study introduces a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as discrete shape memory alloy (SMA) wires and viscoelastic layers. The SMA constitutive model is adopted and developed based on carried out experimental tests (i.e., calorimetry and tensile tests) on Ni-rich Nitinol alloy samples. Pseudoelastic, pseudoplastic, strain recovery and de-twinning phenomena are perceived experimentally. The presented model characterizes pseudoelastic response of shape memory alloys. The current finite element formulation is based on an incremental updated Lagrangian (UL) approach along with the Newmark's integration technique. The used sandwich element is capable of accurate modeling of the viscoelastic core damping behavior, as a result of independent rotation of element's layers. Also, the creep functions regarding to the viscoelastic constitutive model are estimated using Dirichlet-Prony series. Employing the state variables, the viscoelastic deferred strain is presented in a proper incremental form. A nonlinear FE program is developed to assess the proposed procedure. Obtained results demonstrate that quick vibration mitigation may be possible using visco-pseudo-elastic dampers while overcoming their individual drawbacks.

Gennady Alekseevich Leonov (1947 – 2018) – Corresponding member of the Russian Academy of Sciences, Foreign Member of the Finnish Academy of Science and Letters, a Council Member of International Federation of Automatic Control, the Highly Cited Mathematician of the Russian Federation, a bearer of many notable awards – passed away on April 23, 2018 after a short battle with a grievous illness. This paper is written in his memory. The authors remember Prof. Leonov as eminent scholar, admired teacher, and unconventional administrator.

The results of dynamic tests of the TiNi and CuAlNi shape memory alloys are given. Compressive and tensile tests of the TiNi alloy were carried out in the temperature range of 20–300 °C. A significant change was revealed in the elastic modulus before the dislocation plastic flow and the dislocation yield stress with a change in the test temperature in the range of the reverse martensitic transformation.

The influence of aging of TiNi-based shape memory alloy (SMA) specimens on the one-way and two-way shape memory (TWSM) is studied experimentally and simulated with the use of a microstructural model. Experiments show that a long-time storage of preliminarily strained TiNi specimens does not change the strain recovery on heating. At the same time, the strain stroke due to the realization of the TWSM is bigger than before aging. Computer modeling of these phenomena is done within the frames of a microstructural model, in which the macroscopic strain is considered to be the average of the micro-strains–strains of micro-volumes. The irreversible strains are described from the standpoint of the plastic flow theory. Isotropic hardening and kinematic hardening are taken into account and are related to scattered and oriented deformation defects. To describe the effects of aging, special terms are introduced into the evolution equations for the defect densities. Thus, modified equations are able to account for a decrease of the yield limit due to a decrease of the deformation defect densities. The results of modeling show a good qualitative agreement with the experimental data, particularly an increase of the TWSM deformation after aging.

The influence of long-term storage of TiNi-based and CuZnAl alloys on their functional properties was investigated. It was established that during 30years' storage of TiNiFe thermomechanical couplings, the stresses in them practically did not decrease. Couplings with CuZnAl alloy sleeves during storage weakened slightly. The one-way shape memory effect in equiatomic TiNi alloy did not change after 25years. It was found that the value of two-way shape memory effect in the first cycle after storage at room temperature in martensitic state for more than 15years was higher than before storage.

Functional properties of conical working elements of the holding and release device for space application needed to control the device were investigated. The elements had 45 mm in diameter, 11 mm in height and 2 mm in thickness, and were made of TiNi shape memory alloy with characteristic temperatures of martensitic transformations Mf = 30^oC; Ms = 45^oC; As =55^oC; Af = 75^oC. Constraint forces and displacement recovery of the conical working elements as functions of the temperature were obtained. It was found that the friction loss for two conical elements put one in the other one reach 15%. A simple graphical method to evaluate the displacement recovery and constraint forces of such conical working elements needed to control the device is proposed.

The influence of prestrained material storage in the martensitic state on the two-way shape memory effect was investigated. The study was conducted on cylindrical specimens of equiatomic TiNi alloy (Ms =74°C), prestrained by compression: with high strain rate from 750 to 1000 s-1 and quasi-statically with strain rate 10-3 s-1. The storage time was almost 17 years. The dynamic and quasi-static case were compared. It was found that after the long storage time, the value of the two-way shape memory effect increases. Increase of two-way shape memory could be associated with relaxation of the internal stresses during storage.

The stresses generated by implants strongly affect the surrounding tissues’ reaction, which determines the biocompatibility of a construction. Some examples of osteoblasts’ development under compressive macro-stresses typical for the clamping slit-rings are given in this paper. A simplified X-ray diffraction method for measuring stresses generated by such constructions is considered. The method is based on the approximation of the dependence of the relative strain of an experimental crystal lattice on the diffraction angle θ by the Nelson-Riley linear function with extrapolation to θ=90° and allows determination of an average strain value in the direction normal to a construction surface. Using the example of a clamping slit-ring used for oblique bone fracture treatment, the paper shows that despite the peculiarities of macro-stress generation caused by incomplete restoration of such a construction's initial shape (incomplete reverse martensitic transformation), the stress state of a construction’s surface can be considered as a plane-stress state characterized by the typical relationship between a strain perpendicular to a surface and the principal stresses. The advantages of the method are discussed: the increase in the number of experimental diffraction peaks (including weak-intensity peaks) used for an average relative strain measurement, the feasibility of using Young’s modulus and Poisson’s coefficient determined by mechanical tests; the possibility of controlling macro-stresses generated by constructions of any complicated shape and of any phase composition. The macro-stresses measured by the elaborated method are shown to correspond with high precision to the stresses obtained by engineering calculations.

Results of the microstructural modeling of high strain rate isothermal straining of an equiatomic TiNi alloy at different structural conditions using the formulae for strain rate dependencies of dislocation yield limit are presented. Simulations were conducted in the temperature range of 20–300°C. It was shown that the calculated values of the phase and dislocation yield stress in the martensitic and austenitic conditions with a good accuracy correspond to the experimental values. The mechanical behavior of the alloy in the entire investigated temperature range was described using only one pair of constants in strain rate sensitivity of dislocation yield limit.

The chapter is devoted to a study of the influence of neutron irradiation on the martensitic transformations and shape memory effects in TiNi-based shape memory alloys. Irradiation of the samples was carried out in the low-temperature helium loop of a WWR-M fusion reactor at Petersburg Nuclear Physics Institute in Gatchina (Russia). The experimental data showed that the variation in transformation temperatures depended on the irradiation temperature. The main factors influencing the variation in transformation temperatures during irradiation were disordering of the solid solution at low temperatures, radiation ordering at high temperatures, and thermally activated annealing of radiation damage. All of these mechanisms were taken into account in the differential equation given in the present work for description of the transformation temperature variation during irradiation at different temperatures. It was found that irradiation up to a fluence of 7⋅1018 cm-2 did not suppress the transformation plasticity and shape memory effects in TiNi alloy in spite of the variation in transformation temperatures. It was observed that the shape memory effect may be initiated by irradiation up to a fluence of 5⋅1020 cm-2 at a constant temperature (under isothermal conditions) due to a decrease in transformation temperatures.

The effect of metastable austenite straining on the basic functional properties of an NiTi alloy in quasi-equilibrium state was studied. Straining of austenite in a pre-martensitic state was shown to result in improvement of one-way and two-way shape memory effects (OWSME and TWSME). This improvement took place after straining in a narrow temperature range, and its manifestation at quasi-static and high-rate tensile tests was different: the increment of both characteristics was sufficiently large after quasi-static straining, but smaller after high-rate straining. Straining at temperatures that deviated significantly from the Ms temperature led to deterioration of OWSME and TWSME.

The mechanical behavior of the binary polycrystalline NiTi alloy with a quasi-equilibrium structure has been considered in the course of the high-strain-rate extension in a temperature range of 20–300°C. The quasi-equilibrium structure, which is necessary to ensure the long-term stability of special properties of the alloy, was achieved using aging, after which both the forward and reverse martensitic transformations exhibited a multistage character and the phase composition at room temperature was characterized by the presence of R and B19′ martensites. To separate the contributions that come from the equilibrium structure and from the high rate of tension to the mechanical behavior of the alloy, a comparative analysis of the diagrams of high-strain-rate and quasi-static tension has been performed. It has been shown that the action of several mechanisms of reversible deformation is determined by the specific features of the equilibrium structure, and the level of stresses at which these mechanisms are developed is controlled by the rate of tension. The results of the X-ray diffraction study of the phase composition of the alloy samples after high-strain-rate tension, which make it possible to conclude that the mechanical behavior of martensite and austenite upon the dynamic tension of the alloy is determined by the development of stress-induced R → B19′, B2 → R, and B2 → B19′ transformations and by the processes of the detwinning and reorientation of crystals of B19′ martensite, are given.

The results of the comparative study of a quasi-equilibrium NiTi alloy's thermo-mechanical response to high-rate and quasi-static straining in the temperature range of 100-300 degrees C, which included the A(f) and the M-d temperatures, are considered. The existence of B2 -> B19' and B2 -> R -> B19' martensitic transformations, associated with the heterogeneous distribution of Ni4Ti3 precipitates is shown to result in shaping of martensitic and austenitic two-way shape memories, the simultaneous presence of which determines the reversing shape memory effect. The suppression of stress-induced B2 B19' transformation at temperatures higher than the Md temperature resulted in austenitic two-way shape memory only. Distinct dependences on the temperature of the critical stresses that initiate B2 -> B19' and B2 -> R -> B19' martensitic transformations in austenite are shown to be the reason for the participation of the irreversible mechanisms of straining at the earliest stages of tension, whatever the strain-rate applied, thus annihilating the distinctions between the quasi-static and high-rate straining processes. As a result, the thermo-mechanical properties acquired after tension become practically independent of the strain-rate.

TiNi shape memory alloys are nowadays widely used in engineering and medicine. The unique capabilities of this material are particularly apparent in applications for space technology. One of the actual present problems is the design of thermosensitive devices for space applications. In this work, we investigated a TiNi alloy as a working element material for the thermosensitive wire drive as an actuator. An optimum thermomechanical treatment of NiTi alloys was selected based on the analysis of functional and mechanical properties. It consists of a multi-cycle implementation of transformation plasticity under 220 MPa constant stress and a shape memory effect in the free state.

A recent trend for application of shape memory alloys is concerned with the development of micro- and nano-scale devices where increasingly more precise effects caused by reversible martensitic transformations are taken into consideration or used. As a result, effects finer than one-way shape memory become of greater interest and relevance for practical use. Among them the reversible effects can be mentioned that represent non-monotonic strain behavior during a monotonic change of temperature. Procedures of initiation of reversible effects are rather complex for realisation. The key conditions are the possibility of formation of two-way shape memory of two types – martensitic and austenitic, or the availability of multi-stage martensitic transformation for the alloy. Also, the martensitic and austenitic two-way shape memory effects should be realised either in different temperature intervals or at different parts of the specimen. The authors propose a relatively simpler way of obtaining the reversible two-way shape memory by straining of the specimen in austenitic state. It is also shown that apart from the reversible two-way shape memory effect the other two of austenitic or martensitic type can be realised independently of each other. It is established that the reversible two-way shape memory deteriorates with the number of cycles. The two-way shape memory of austenitic type is less steady with thermocycling than the two-way shape memory of martensitic type, which leads to the disappearance of deformation reverse during cooling.