W.K. Nowacki

Characteristics of energy storage and dissipation in TiNi shape memory alloy

Abstract The characteristics of energy storage and dissipation in TiNi shape memory alloys were investigated experimentally based on the superelastic properties under various thermomechanical loading conditions. The influence of strain rate, cyclic loading and temperature-controlled condition on the characteristics of energy storage and dissipation of the material was investigated. Temperature on the surface of the material was observed and the influence of variation in temperature on the characteristics was clarified. The results obtained can be summarized as follows. (1) In the case of low strain rate, the stress plateaus appear on the stress-strain curves due to the martensitic transformation and the reverse transformation during loading and unloading. In the case of high strain rate, the slopes of the stress–strain curves are steep in the phase-transformation regions during loading and unloading. The recoverable strain energy per unit volume increases in proportion to temperature, but the dissipated work per unit volume depends slightly on temperature. In the case of low strain rate, the recoverable strain energy and dissipated work do not depend on both strain rate and the temperature-controlledcondition. (2) In the case of high strain rate, while the recoverable strain energy density decreases and dissipated work density increases in proportion to strain rate under the temperature-controlled condition, the recoverable strain energy density increases and dissipated work density decreases under the temperature-uncontrolled condition. In the case of the temperature-uncontrolled condition, temperature varies significantly due to the martensitic transformation and therefore thecharacteristics of energy storage and dissipation differ from these under the temperature-controlled condition. (3) In thecase of cyclic loading, both the recoverable strain energy and dissipated work decrease in the early 20 cycles, but change slightly thereafter. (4) The influence of strain rate, cyclic loading and the environment on the characteristics of energy storage and dissipation is important to be considered in the design of shape memory alloy elements.

Investigation of nucleation and propagation of phase transitions in TiNi SMA

The attention of the present paper is focused on the aid provided by infrared thermography, for spectacular investigation of nucleation and further development of the stress induced phase transitions in TiNi shape memory alloy. This is a qualitative analysis aimed to verify the feasibility of further study in the application of IR for studying change phenomena. To this end, the material stress-strain curves, obtained during tension test with various strain rates, were completed by the temperature characteristics. The temperature distributions on the specimens surface were determined by using an infrared camera. A heterogeneous temperature distribution, related to the nucleation and development of the new martensite phase, were registered and analyzed. A significant temperature increase, up to 30 K was registered during the martensite transformation. Similar effects of the heterogeneous temperature distribution were observed during unloading, while the reverse transformation, austenite into martensite, tooks place. The reverse transformation was accompanied, in turn, by a temperature decrease, of up to 10 K.

Thermomechanical properties of shape memory polymer subjected to tension in various conditions

Thermomechanical and functional properties of shape memory polyurethane are presented. A background of the polymer shape memory effects is described. Elastic modulus at various temperatures and the polyurethane parameters important for the practical applications, called shape fixity and shape recovery, are derived. Taking advantages from the high quality testing machine and infrared camera, mechanical characteristics and temperature changes of the shape memory polyurethane specimens subjected to tension test carried out in various conditions are clarified and analyzed. Stress-strain curves and the relevant temperature changes are recorded both in the elastic and the plastic ranges of deformation. A significant value of a thermoelastic effect is observed. Taking into account the obtained experimental data from the polyurethane tension tests performed at room temperature, followed by the heating above its glass transition temperature, the shape memory polyurethane properties are studied.

Thermoelastic and thermoplastic effects investigated in steel, polyamide, and shape memory alloys

This research is an experimental confirmation of the theoretical model, presented by M.G. Beghi, C.E. Bottani and G. Cagliotti, realized due to the contact less method of temperature measurement and conversion. The effects of thermomechanical coupling occurring in austenitic steel, polyamide and shape memory alloys were examined. The change of character of the samples temperature was applied as a criterion for the limit between the elastic and plastic regimes. The thermal effects concomitant with thermoelastic unloading were also quite precisely evaluated. The obtained results indicate on both qualitative and quantitative differences between thermomechanical behaviors of the materials subjected to deformation. TiNi shape memory alloy was tested both at room and at elevated temperatures. The temperature distribution on the surface of specimen examined at ambient temperature was uniform, while for the specimen deformed at elevated temperature the areas of higher temperature were registered. There are probably the regions of creation and developing of the new - martensite phase.

SMA Thin Strip for Rotary-Driving Element

If a shape-memory alloy (SMA) thin strip is applied as an element subjected to torsion, a rotary driving element with a simple mechanism can be developed. The torsion tests were carried out for the SMA thin strip. Torque and recovery torque, both increase in proportion to the angle of twist and temperature. The recoverable strain energy increases in proportion to temperature. The dissipated work decreases slightly with an increase in temperature. A means of opening and closing a door with an element driven by an SMA thin strip is demonstrated.

Superelastic Deformation Properties of TiNi Shape Memory Alloy

The characteristics of energy storage and dissipation in TiNi shape memory alloys were investigated experimentally based on the superelastic properties under various thermomechanical loading conditions. The results obtained can be summarized as follows. (1) The recoverable strain energy increases in proportion to the rise in temperature, but the dissipated work per unit volume depends slightly on temperature. In the case of low strain rates, the recoverable strain energy and dissipated work do not depend on both the strain rate and the temperature-controlled condition. (2) In the case of high strain rates, while the recoverable strain energy decreases and the dissipated work increases in proportion to the rise in strain rate under the temperature-controlled condition, the recoverable strain energy increases and the dissipated work decreases under the temperatureuncontrolled condition.

THERMOPLASTIC ANALYSIS OF NORMAL IMPACT OF LONG CYLINDRICAL SPECIMEN: EXPERIMENT AND COMPARISON WITH THE NUMERICAL CALCULATION

The objective of this paper is to compare the temperature and the deformation fields in the cylindrical specimens (e.g., aluminum alloys), determined in the Taylor impact tests, with the numerical solutions. The temperature and deformation fields are caused by dynamic plastic deformation at high strain rates in the presence of finite strains. It is assumed that the process is locally adiabatic and associated with the axisymmetric deformations. Additionally, within the framework of Mandels formalism, the general adiabatic plastic flow laws are derived for isotropic rate-dependent solids. They reduce to a simple form for the considered problem. The testing stand was based on the Hopkinsons pressure bar system and AGA thermovision set. The details of the experiment and the analysis of the experimental results are presented. The experimental results are compared with the numerical solutions.

Immunoglobulins of colostrum—VI. comparative studies of cytophilic properties of bovine serum and colostral IgG

In our previous studies, using physical-chemical and serological methods, substantial differences between bovine serum and colostral IgG, especially IgG2, have been shown. The structural differences were localized in the Fc region of immunoglobulins studied. The present comparative studies were undertaken to determine whether structural differences in the Fc region of bovine serum and colostral IgG are reflected in the interaction of these immunoglobulins with the guinea-pig peritoneal macrophage Fc gamma receptor. It was found that binding of bovine serum and colostral IgG1 was a saturable process and only quantitative differences in the mode of binding to the Fc receptor were observed. There is, however, a big difference in cytophilic activity of bovine IgG2--no saturable and reversible binding is observed in the case of bovine serum IgG2.

LOCALIZATION OF THERMOPLASTIC DEFORMATIONS IN THE CASE OF SIMPLE SHEAR

The results of tests of quasi-static and dynamic finite thermoelastoplastic plane shear is discussed. Use is made of a new shear device in which loading and displacements are controlled in compression. Using the thermovision technique the temperature changes of the sheared paths have been registered for various shear rates. The rate-independent constitutive relations are formulated for elastic-plastic metallic solids at finite strain. The constitutive relations are considered for an adiabatic process with combined isotropic-kinematic hardening. The analogous initial-boundary-value problem as in the experiment of simple shear is formulated for finite deformations. An exceptional homogeneity of the permanent strain and temperature fields is observed in experiments and numerical simulations, over the total length of the specimens, when the strain is less than 70%. For the largest deformations the zones of strain localization are observed