Моделирование высокоскоростной работы композитного наноактюатора на основе эффекта памяти формы с минимальным термическим дрейфом

The mechanism of elastic calorific effect in crystals of alloys with SME is theoretically discussed within the framework of the theory of diffuse thermoelastic martensitic transitions, that the structural transitions in alloys with shape memory effect (SME) are. The theory provides an adequate description of the elastic calorific effect under adiabatic unloading of the crystal and stable behavior of the martensitic transition. Flexibility of the theory is also applicable to kinetically unstable (with a burst) martensitic transitions caused by structural features of the crystal, as is the case, according to literature, of Ni50Fe19Ga27Co4 alloy crystal compression along the direction of [011]. Key words: alloys with SME, elastic calorific effect, thermoelastic martensitic transitions, stable and unstable kinetics of martensitic transition.

Phase transformation and structure of functionally graded Ni–Ti bi-layer thin films with two-way shape memory effect

Shape memory alloys (SMAs) belong to a group of functional materials with the unique property of “remembering” the shape they had before pseudoplastic deformation. Such an effect is based on crystallographic reversible thermo-elastic martensitic transformation. There are two crystal phases in SMAs: the austenite phase (stable at high temperature) and the martensite phase (stable at low temperature). Austenite to martensite phase transformation can be obtained by mechanical (loading) and thermal methods (heating and cooling). During martensitic transformation, no diffusive process is involved, only inelastic deformation of the crystal structure. When the shape memory alloy passes through the phase transformation, the alloy transforms from high ordered phase (austenite) to low ordered phase (martensite). There are two types of martensite transformations. First is temperature-induced martensite, which is also called self-accommodating (twinned) martensite. The second is stress-induced martensite, also called detwinned martensite. The entire austenite to martensite transformation cycle can be described with four characteristic temperatures: M_s – martensite start temperature, Mf – martensite finish temperature, As – austenite start temperature, and Af – austenite finish temperature. The main factors influencing transformation temperatures are chemical composition, heat treatment procedure, cooling speed, grain size, and number of transformation cycles. As a result of martensitic transformation in SMAs, several thermomechanical phenomena may occur: pseudoelasticity, shape memory effect (one-way and two-way SME) and rubber-like behavior. Pseudoelasticity occurs when the SMA is subjected to a mechanical loading at a constant temperature above Af. The second thermomechanical behaviour that can be observed in SMA is the shape memory effect (SME), mainly one-way SME, which is the most commonly used SME. When the sample is subjected to a mechanical loading, the stress reaches a critical value and the transformation of twinned martensite into detwinned martensite begins and finishes when the loading process is finished. When the loading-unloading process is finished, the SMA presents a residual strain recoverable by alloy heating, which induces the reverse phase transformation. As a result, the alloy recovers to its original shape. In this paper, a review of thermomechanical properties of shape memory alloys and general characteristics of martensite transformations is shown.

Processing, properties and applications of Ni-Ti-Fe shape memory alloys

Shape memory alloys (SMAs) exhibit the ability to absorb large dynamic loads and, therefore, are excellent candidates for structural components where impact loading is expected. Compared to the large amount of research on the shape memory effect and/or pseudoelasticity of polycrystalline SMAs under quasi-static loading conditions, studies on dynamic loading are limited. Experimental research shows an apparent difference between the quasi-static and high strain rate deformation of SMAs. Research reveals that the martensitic phase transformation is strain rate sensitive. The mechanism for the martensitic phase transformation in SMAs during high strain rate deformation is still unclear. Many of the existing high strain rate models assume that the latent heat generated during deformation contributes to the change in the stress-strain behavior during dynamic loading, which is insufficient to explain the large stress observed during phase transformation under high strain rate deformation. Meanwhile, the relationship between the phase front velocity and strain rate has been studied. In this dissertation, a new resistance to phase transformation during high strain rate deformation is discussed and the relationship between the driving force for phase transformation and phase front velocity is established. With consideration of the newly defined resistance to phase transformation, a new model for phase transformation of SMAs during high strain rate deformation is presented and validated based on experimental results from an austenitic NiTi SMA. Stress, strain, and martensitic volume fraction distribution during high strain rate deformation are simulated using finite element analysis software ABAQUS/standard. For the first time, this dissertation presents a theoretical study of the microscopic band structure during high strain rate compressive deformation. The microscopic transformation band is generated by the phase front and leads to minor fluctuations in sample deformation. The strain rate effect on phase transformation is studied using the model. Both the starting stress for transformation and the slope of the stress-strain curve during phase transformation increase with increasing strain rate.

Considerations of sample size in medical research

Alloys with the shape memory effect have recently found application in engineering. Specifically, parts made of such alloys can be actuating members in structures of thermoregulators and thermorelays. It is known that the shape memory effect is realized in alloys with a thermoelastic martensite transformation. When heated, specimens strained in a martensite state recover their initial shape partially or completely as a result of a reverse martensite transformation. If an external load is applied in thermocycling, the shape will be changed both in heating and in cooling, i.e., recovered in the reverse martensite transformation and deformed under the effect of the external load in the direct martensite transformation. This change in shape is commonly said to be reversible. The aim of the present work consists in analyzing the effect of deformation in the martensite state prior to thermocycling and of an external load during the thermocycling on the reversible change of shape in Mn−Cu-base alloys.

In the article there is presented a brief overview of combined systematic investigations of the alloys exhibiting thermoelastic martensitic transformations (TMTs). As is known, such alloys are distinguished by a whole number of specific one-and multi-fold-reversibility shape-memory (SM) effects occurring upon changing temperature, pressure, magnetic field, at the background of superplasticity and highly reversible deformation of transformation under a load or its relieving.There have been considered the alloys classification, the thermodynamical and kinetic aspects of TMTs, the origin and structural mechanisms of realization of multivarious pre-transition phenomena and TMTs proper, the influence of complex alloying, the peculiar features of a structure, the physico-mechanical properties and methods of production of the alloys most promising from the viewpoint of application. For this purpose there were employed structural methods of the X-ray diffraction (XRD) structure-phase analysis, neutron diffraction analysis, transmission and scanning electron microscopy techniques of high resolution, together with studying texture and atomic composition, as well as measuring a number of physical properties and SM-effect characteristics.The effect of the alloying and external actions of different origin on the magnetic and structural phase transformations and properties of the studied alloys with the magnetically, thermally, and mechanically controlled manifestations of the shape memory is discussed. A sequence of the TMTs with the formation of different martensitic phases, as well as the crystallographic structure and crystal-geometry specific features of the formation of these phases is described. The phase diagrams of the magnetic and martensitic transformations in a number of binary, ternary, and quaternary alloys synthesized via different schemes of alloying are presented.On the example of the binary and doped alloys TiNi it has been shown that an employment of thermo-mechanical treatments of the alloys via multiple or repeated torsion under pressure, rolling or drawing leads to their high-level strengthening and grain refinement (up to amorphization). In this case the use of low-temperature annealing provides for both the creation in the alloys of the homogeneous nanostructured state with a controllable grain size already in the interval of 50–200 nm and efficient regulation of physico-mechanical properties with retaining comparably high values of the parameters of SM, including deformation-, temperature-, and force-related.There has been revealed the effect of the grain size on the critical temperatures of TMTs and, as a consequence, on the TMT-stipulated SMEs. On this basement, in dependence of the grain size, the poly-packet, mono-packet twinned or single-crystal structures of martensite can be realized.There are discussed an experimentally revealed deformation-induced atomic disordering in Heusler alloys with self-forming a nanocrystalline fcc (A1) structure and amorphization in the alloys of titanium nickelide, as well as long-range order recovery in them taking place in the course of low-temperature annealing in conditions of retaining of the nanostructured state of austenite and at feasibility of cascade occurrence of TMTs and SMEs. It has been shown that the use of super-rapid quenching (SRQ) via employment of a melt spinning technique makes it possible to produce ductile submicrocrystalline ribbons of the Heusler Ni2MnGa-based alloys with magnetically controllable TMTs. For a number of alloys based on titanium nickelide the effect of SRQ on the internal structure, grain refinement, and amorphization has been considered. The reasons of the amorphization and ways of subsequent nanostructurization of the alloys under investigation are discussed.

Martensitic phase transformation of magnetron sputtered nanostructured Ni–Mn–In ferromagnetic shape memory alloy thin films

In copper-based shape memory alloys (SMAs), some exceptional phenomena, such as the shape memory effect (SME) or superelasticity (SE), are observable. However, commercial aluminum bronzes, Cu3Al-based alloys, do not present these functional properties (SME and/or SE) in their original state. Thus, since one of the main copper-based SMA systems is the Cu-Al-Ni alloy, this paper aims to analyze the modification of these commercial aluminum bronzes to SMA by the addition small amounts of Cu, Al and/or Ni. These modified bronzes were reprocessed by induction melting and injected by centrifugation into a ceramic coating mold. The modifications were made to determine the nominal composition for a Cu-13,0Al-4,0Ni (%wt) SMA. The effectiveness of the modifications was verified by differential scanning calorimetry (DSC) thermal analysis. All modified Cu-Al-Ni bronzes presented DSC peaks of the thermoelastic martensitic phase transformation, showing that SMA behavior was achieved, while the non-modified bronzes revealed no transformation. These results were supported by Vickers hardness (HV), X-ray diffraction (XRD), semi quantitative composition by EDS analysis and optical microscopy.

294 Background: Economic evaluations in oncology aim to assess the value of new therapies in the long term based on clinical trial data that often have restricted follow-up times (< 5 years) and small sample sizes (< 500 patients). This requires the use of extrapolation assumptions on long-term survival that go beyond the observed data. In this analysis, differences in survival extrapolation methods are tested in samples of sizes and follow-up reflecting typical clinical trials against a background of known survival in prostate cancer from a US based cancer registry. Methods: Data from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) registry on long-term survival in patients with stage IV prostate cancer were employed. The data set comprised those patients diagnosed between 1988 and 2003, with follow-up data available until 2012. Additional survival for those who received surgery (compared to those who did not), was estimated based on extrapolations using standard parametric statistical models (exponential, Weibull, log-logistic, log-normal, Gamma) fitted to the observed data. Survival analyses were run for 5 sample size scenarios (n = 27,670, 1000, 500, 200, 50) and 6 follow-up scenarios (follow-up years = 25, 20, 10, 5, 2, 1) yielding 30 combination scenarios. Performance of the methods was tested relative to the maximum follow-up, maximum sample size scenario (i.e. reference case) from the SEER registry. Results: Log-logistic and log-normal models were associated with flat tails which led to inflated survival estimations. For scenarios with smaller sizes, gamma models often did not converge. Exponential models were the most frequently reported as best model fit (in approximately 50% of scenarios). Also, gains in OS were consistent when exponential models were selected, and closely matched gain in OS from the reference case. Conclusions: Since clinical trials in oncology are often associated with small patient sample sizes and restricted follow-up, selecting an exponential model may lead to the most consistent and stable results based on the experiment constructed here. Further research should confirm these results for other types of cancer.

The developed design of an automobile hinge for vehicles of category M1 and N1 is shown with the creation of a model in the SolidWorks software package by studying its strength characteristics in the SolidWorks Simulations application according to the technical regulation TR CU 018/2011 On the safety of wheeled vehicles (according to to the requirements of TR CU 018/2011, the assessment of compliance with safety requirements is carried out in accordance with UN Regulations No. 11), in comparison with the model of a standard automobile hinge. Distribution diagrams of loads, stresses, displacements and deformations of a standard loop and proposed structures made of materials with shape memory effect are analyzed.KeywordsSoftware package SolidWorks and SolidWorks SimulationsTwo-link car door hingeMaterials with thermoelastic phase transformationsImproving post-accident safety

The shape memory alloys (SMAs) have recently been recognized as reliable basement of the technology of mechanical nanotools with still non determined minimal size. Among them the intermetallic alloy Ti(NiCu) give promising possibilities to create the reconfigurable micro- and nanostructures with shape memory effect (SME) capable to produce mechanical work on nanoscale. In the present report the review of the basic physical phenomena, which provide the possibility for the application of nanostructured SMA Ti(NiCu) for creating of micro and nanotools is given. The preliminary strained layered composites of SMAs are discussed which provide the multiple reversible actuation of a SMA based tool. Fundamental studies devoted to search for minimal size, at which martensitic phase transition and controllable actuation of SMA based tools take place are described. The technology of SMAs treatment by FIB-CVD gives the possibility to create different kinds of micro and nanotools, like nano- tweezers, grippers, pinchers, screws etc. These micro-nanotools have active SME layer with the thickness from tenths nm to 1 µm The continuous bending actuation threshold frequency of the SMA based thermally controlled nanoactuator is proved to exceed 8000 Hz. The new mechanical nanotools with SME give possibility to provide 3D nanomanipulation of the real nano-objects such as CNTs, different nanowires, nanowhiskers and also bio-nanoobjects such as DNA, etc. One of very interesting fundamental physical question which arises at nano-manipulation is the restriction due to influence of Casimir and van der Waals forces between the interacting nanotools and objects to be manipulated.

Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to systematically study the structure and the chemical and phase composition of the Ni50Ti38Hf12 alloy synthesized by rapid quenching from the melt and subjected to various heat treatments. The critical temperatures of the devitrification of the initially amorphous rapidly quenched alloy and the B2 ↔ B19′ thermoelastic martensitic transformations have been determined. The lattice parameters of the B2 austenite and thermoelastic B19′ martensite have been measured. The main features of the formation of an ultrafine-grained structure in the alloy and the subsequent phase transformations (martensitic transformation and the decomposition with the formation of an intermetallic phase of the (Ti,Hf)2Ni type) have been studied depending on the regimes of heat treatment. Based on the results of measurements of mechanical properties upon tension (σM, σu, and δ) and the shape-memory effects (degree of shape recovery depending on the deformation by bending; and magnitude of the reversible strain erev), regimes for obtaining high-strength and plastic states of the alloy with a shape-memory effect have been established.

In the present research, in contrast to the available papers, not only the superelasticity but also the shape memory effects are taken into account in determination of the impact responses. At the same time, in addition to modifying Brinson’s model for the shape memory alloys (SMAs), to include new parameters and loading events, and Hertz contact law, distributions of the SMA phases are considered to be both localized and time-dependent. Furthermore, effects of the impact-induced heat generation and mechanical energy on the resulting histories of the martensite phase volume fraction, stress-strain, temperature, lateral deflection, and contact force are investigated. The generated heat in the SMA wires during the impact is determined through using a Helmholtz free energy function including the latent heat of the phase transformation. The resulting governing equations are solved by the finite element method. The nonlinear refined constitutive laws are solved through a return-mapping Newton-Raphson procedure. Results reveal that incorporation of the heat generation effects is significant in medium/high-velocity impacts or when the stress field is almost uniform.