Papers by Keyword: Shape Memory

Abstract: Liquid crystalline polyurethanes (LCPU) were prepared from 4,4’-methylenediphenyl diisocyanate (MDI), 1,6-hexanediol (HDO), 2,2-dimethylol propionic acid (DMPA) and polytetramethylene ether glycol (PTMG). The experiments synthesized three liquid crystalline polyurethane films with different soft/hard segment ratio. Chemical and structural characterization of the polyurethanes were investigated by Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, differential scanning calorimeter and polarized microscopy respectively. Swelling rate and shape memory property were tested. The results indicated that the polyurethane with 62% soft segment and large group of carboxyl displayed excellent swelling and shape memory properties, and the shape recovery rate reached 100%. It was found that the crystallinity, thermal stability decreased and the temperature flexibility, water absorption and shape recovery rate increased with the increase of polytetramethylene ether glycol.

Abstract: The report provides designs of actuators from the shape memory material-nitinol. It is proposed to use rods, wire, sheets and tape as working elements of the actuators. Special attention is paid to the designs of composite multil-element actuators, working elements of which are connected in parallel or in series. The experimental technique and results of experiments on evaluation of stresses developed by such actuators are given. It is shown that using the composite actuators from thin working elements facilitates control over their heating and cooling.

Abstract: In the paper is shown the study of super elasticity of Ni-Ti shape memory alloys from the point of view of stored energy, strain dependencies and martensitic transformations that influence superelasticity of Ni-Ti shape memory alloys [1]. We also present the influence of temperature and alloy composition on the properties of Ni-Ti alloys after plastic deformation and heat treating [2].

Abstract: This microstructural model of the functional-mechanical behavior of shape memory alloys (SMA) includes a description of the reversible phase deformation, microplastic deformation due to the accommodation of martensite and the evolution of the deformation defects. The laws of these phenomena are formulated in terms of the generalized thermodynamic forces. The microplastic flow rule accounts for isotropic and kinematic hardening, which are related to the accumulation of the deformation defects. The model gives a good description both of reversible and irreversible deformation under one-side or cyclic thermomechanical loading of SMA and opens a way for the fatigue life prediction. The model can be applied for solving of the mechanical problems for SMA parts such as dampers or base isolators used in seismic protection devices.

Abstract: Nowadays, ferromagnetic shape memory Heusler alloys are ones of famous multifunctional materials exhibiting many interesting features in the temperature interval of the martensitic transformation due to the strong interrelation between crystal structure and magnetic order. The multiferroic, magnetoresistive, martensitic and related magnetic shape-memory behavior as well as magnetocaloric properties are examples of these unique features. Generally, tuning of both structural and magnetic transition temperatures can be useful to achieve better functional properties. Today, the optimization problem of Heusler compounds is of a great importance. In this chapter, we review the most important features of ternary and quaternary ferromagnetic shape memory Ni-Mn-In and Ni-Mn-In-Z materials, which are experimentally and theoretically obtained in the last three years. We discuss the experiments devoted to the study of phase diagrams, thermomagnetizations, magnetic field and stress induced strains, magnetoresistance and magnetocaloric effects. The theoretical investigations of magnetic and structural properties are reviewed in the framework of the phenomenological approach, first-principles and Monte Carlo methods.

Abstract: Cu22Zn4.6Al shape memory alloy shows memory phenomenon after quenching from dual phase region. Amount of shape memory effect continuously decreases with raised quenching temperature. Decrease is caused by increasing of amount of non-thermoelastic martensite in structure [. Approximately above 700°C there is no effect and martensite is non-thermoleastic. Non-thermoelastic martesite decomposes to alpha and gamma/beta phases at heating at elevated temperatures.[ This effect can be used for modification of structure and thus mechanical and shape memory properties. Some various types of structures were obtained and mechanical and shape memory properties were evaluated. Using of decomposition of non-thermoelastic martensite allows to obtain fine structure with the same amount of alpha phase and martensite as in basic state. This type of structure has better shape memory properties and higher mechanical properties.

Abstract: Ni-Ti-Nb system alloys show wide shape memory hysteresis, suitable for assembly applications. The microstructure is composed by NiTi matrix (with some dissolved Nb) and Nb dispersed particles (with some Ni and Ti content). These particles are to cause the hysteresis widening. This work evaluates the microstructure evolution during wire fabrication process of equiatomic Ni and Ti alloys with increasing Nb content (1.5, 3.0, 6.0 and 9,0%at.). It is shown that as-cast alloys with up to 9% at.Nb and near equiatomic Ni:Ti relation show three main microconstituents: NiTi matrix phase, interdendritic eutectic phase (NiTi + β-Nb) and Ti₃(Ni,Nb)₂ compound precipitates. It was observed that NiTi matrix phase and eutectic phase (NiTi + β-Nb) have ductile behavior while Ti₃(Ni,Nb)₂ compound have fragile behavior. There was not much hardness variation during hot swaging (200-300 HV) due to recovery and recrystallization processes. Mechanical hardening prevailed as the mechanism for increase hardness of cold worked samples from 200 to 450 HV.

Abstract: Shape memory alloys (SMAs) represent a unique class of materials that undergo a reversible phase transformation (martensitic transformation) allowing these materials to display dramatic pseudoelastic stress-induced deformations and shape memory temperature-induced deformations that are recoverable. Among the known shape memory alloys, NiTi is the most commonly used because of its excellent mechanical properties, corrosion resistance and biocompatibility. This work studied the influence of two parameters of heat treatment (temperature and time) on martensite phase transformation temperature (M_S) in a Ni-Ti (48,8 wt % Ti) shape memory alloy, using a factorial design (2²). The aim of our research was to establish a mathematic model of the technological process, useful for controlling of martensite phase transformation temperature. The two factors, temperature and time, have an important influence on M_S.

Abstract: Crystalline grains of TPI distribute in NR/TPI blends in the role of physical crosslinking points and make up for deficiencies of the NR/TPI blending system. The flexibility and strength have been enhanced significantly by increasing the the addition level of TPI. The NR/TPI vulcanizates containing 30% of TPI were found to show the recovery rate of 99.4%, while the shape fixity was close to 100%. The study indicated that the recovery rates of NR/TPI vulcanizates depended to a large extent on the addition level of TPI. The influence of the addition level of TPI on the micro-structure of NR/TPI blends was investigated. In addition, the effects of TPI content on static mechanical properties, dynamic mechanical properties, shape-memory performance and cure characteristics of NR/TPI blends were also discussed.

Abstract: When we use effectively shape memory alloys require knowledge of operational behavior at the thermal stresses and mechanical variables. Measurements performed on a CuZnAl alloy, revealed fatigue properties by considering the size of the maximum load deformation corresponding recovered memory. It requires knowledge in design fatigue behavior of shape memory alloy components after education, fatigue strength by performing partial memory loss or physical destruction. The properties of memory shape alloys recommend their use for complex mechanical applications in domains as follows medicine, robotics, aeronautics, electric contacts, actuators. Shape memory metal alloys in the construction of such installations are subject to mechanical stress, and the thermal stresses, so their inclusion in a computing system fatigue involves consideration of the function performed.