Temperature Memory Effect Research Articles

DSC study on temperature memory effect of NiTi shape memory alloy

A systematic study on the temperature memory effect (TME) in a polycrystalline NiTi shape memory alloy was presented. The investigation was carried out through a series of differential scanning calorimeter (DSC) tests. Two types of tests were conducted, namely single-step test and multi-step test. The influence of the step temperature on the peak/trough temperatures in the subsequent heating process and the associated energy absorption/release in the phase transformations was investigated. Using a simple theoretical model, the exact mechanism behind TME was studied.

Temperature memory effect in two-way shape memory TiNi and TiNiCu springs

An incomplete thermal cycle upon heating in a shape memory alloy (arrested at a temperature between A s and A f ) induced a kinetic stop in the next complete thermal cycle. The kinetic stop temperature is closely related to the previous arrested temperature. This phenomenon is named temperature memory effect (TME). In this article, the TME in two-way shape memory TiNiCu and TiNi springs was investigated by performing either a single incomplete cycle, or a sequence of incomplete cycles. N points of temperatures could be memorized if N times of incomplete cycles on heating were performed with different arrested temperatures in a decreasing order. The capability is enhanced by performing repetitive incomplete cycles with the same temperature, and the TME can be eliminated by appropriate complete transformation cycle. The TME is originated from the relaxation of both the strain energy between martensite and coherent strain between parent phase and martensite.

Temperature memory effect induced by incomplete transformation in TiNi-based shape memory alloy

If the reverse transformation of a shape memory alloy is arrested at a temperature between A s and A f, a kinetic stop will appear in the next complete transformation. The kinetic stop temperature has a close relation with the previous arrest temperature. This phenomenon is called temperature memory effect (TME). In this work, the TME induced by incomplete cycling in Ti–Ni and Ti–Ni–Cu plates, Ti–Ni–Nb bar was systematically investigated by performing either a single incomplete cycle, or a sequence of incomplete cycles with different arrested temperatures. Results showed that the TME is a common phenomenon in shape memory alloys, caused by a partial martensite to parent phase (M → P) transformation. On the contrary, if a partial parent phase to martensite (P → M) transformation was performed by an incomplete cycle on cooling, the next complete P → M transformation did not show any evidence of TME. Results showed that the capability to memorize the temperature is a specific characteristic of both in monoclinic martensite (B19′) and orthorhombic martensite (B19) phase.

Temperature memory effect of Ni47Ti44Nb9 wide hysteresis shape memory alloy

Abstract The temperature memory effect (TME) phenomenon of Ni 47 Ti 44 Nb 9 wide hysteresis shape memory alloy was studied. It was found that TME occurred during the reverse transformation for the thermally-induced martensite (TIM) but not for the stress-induced martensite after incomplete transformation cycling. The reverse transformation temperature interval of TIM can be doubly broadened after 10 incomplete transformation cycles.

Digital predistortion linearizes wireless power amplifiers

When compared to other linearization methods, adaptive DP provides sufficient linearization with less complex RF hardware by depending primarily upon DSP rather than analog manipulation. The adaptive DP system may be implemented in EDA software along with interconnected test equipment (arbitrary RF signal source and vector signal analyzer). Through the use of a training signal, a simple adaptive algorithm may be employed to update the LUT coefficients until an optimum setting is achieved and used to predistort the input to the amplifier. This connected solution approach can provide key information to design engineers for optimizing the DSP architecture of a PA. For future work, other issues are taken into account, such as temperature and electrical memory effects.

Effect of incomplete transformation on the transformation behavior in TiNi shape memory alloys

An incomplete transformation upon heating induces temperature memory effect (TME) in shape memory alloy (SMA) [1]. If a reverse transformation of a SMA is arrested at a temperature between reverse phase transformation start and finish temperatures (i.e., As and Af), a kinetic stop will appear in the next complete transformation cycle. The kinetic stop temperature is a “memory” of the previous arrested temperature. Previously this phenomenon was also named thermal arrest memory effect (TAME) [2] or step-wise martensite to austenite reversible transformation (SMART) [3]. An incomplete transformation upon cooling can induce splitting of the reverse transformation in a sample showing Rphase transformation [4]. In a sample showing R-phase transformation, when the stop temperature arrested in a value between Rf and Ms, the heat flow detected upon following heating only shows one endothermic peak. With decreasing the arrested temperature to a temperature between Ms and Mf, two endothermic peaks (or peak splitting) can be observed upon the following heating. The mechanism of the TME and peak splitting is still unknown. In this work, incomplete transformation upon heating and cooling is performed in TiNi shape memory alloys showing or without showing R-phase transformation. The purpose of this work is to discuss the mechanism of TME and peak splitting. The investigations have been carried out on commercial Ti-49.8at.%Ni wire with a diameter of 0.55 mm, provided by the Northwestern Institute of Non-Ferrous Metal of China, was annealed at 400 ◦C and 550 ◦C for 1 hr followed by air-cooling. Samples with weight of 10 mg were used for differential scanning calorimetry (DSC) measurements. DSC tests (using an equipment of DSC131, Setaram company, France) were performed with a scanning rate of 10 ◦C/min in nitrogen atmosphere. The global transformation behavior of the above samples was measured firstly, and then the incomplete transformation behavior was recorded. Fig. 1 shows the DSC results of TiNi wire annealed at 400 ◦C for 1 hr. The global transformation result (Fig. 1(a)) shows that upon cooling, two-step transformation among austenite, R-phase, and martensite can be observed, while upon heating, only one step transformation between martensite and austenite can be detected. The DSC results with incomplete cycle upon

Temperature memory effect of Ti 50Ni 30Cu 20 (at.%) alloy

After the reverse thermal induced martensitic transformation process of shape memory alloy is arrested at a temperature between the reverse transformation start and finish temperatures ( A s and A f), and then cooled to a temperature below M f, a kinetic stop will occur in the next heat flow curve during the heating process. The kinetic stop is closely related to the arrested temperature. This phenomenon is called temperature memory effect (TME). TME of Ti 50Ni 30Cu 20 (at.%) shape memory alloy with phase transformation between B2 austenite and B19 martensite has been investigated by differential scanning calorimeter in this paper. The results indicate that TME of Ti 50Ni 30Cu 20 alloy only exists in the heating process.

Dynamical Properties of Temperature Chaos and Memory Effect

In the frustrated interaction systems, the nature of ordered configuration can be intrinsically temperature dependent. There, the idea of effective coupling of decorated and frustrated bond plays an important role. The idea of effective coupling is verified in the study of equilibrium properties. We will study how the effective coupling is realized in the dynamical processes, e.g. the relaxation time after a change of temperature. We also study the memory phenomena which have been found in the spin glass.

Temperature memory effect in TiNi-based shape memory alloys

An incomplete thermal cycle upon heating of a shape memory alloy (arrested at a temperature between austenite transformation start and finish temperatures, A s and A f) induced a kinetic stop in the next complete thermal cycle. The kinetic stop temperature was closely related to the previous arrested temperature. This phenomenon is named temperature memory effect (TME). In this work, the TME induced by incomplete cycling in TiNi and TiNiCu ribbons, TiNiCu thin films and TiNiCu wire showing two-way shape memory effect was systematically investigated by performing either a single incomplete cycle, or a sequence of incomplete cycles with different arrested temperatures. Results showed that the TME is a common phenomenon in shape memory alloys, caused by a partial martensite to parent phase (M → P) transformation. N points of temperatures could be memorized if N times of incomplete cycles on heating were performed with different arrested temperatures in a decreasing order. On the contrary, if a partial parent phase to martensite (P → M) transformation was performed by an incomplete cycle on cooling, the next complete P → M transformation did show any evidence of TME. The incomplete cycle of parent phase to R-phase and R-phase to parent phase transformations did not show any evidence of TME. Results showed that the capability to memorize the temperature is a specific characteristic of the martensitic phase, and the decrease in microstrains and elastic energy after ICH procedure has significant contributions to the TME.

Temperature memory effect induced by incomplete transformation in TiNi shape memory alloy

Temperature memory effect can be induced by incomplete transformation upon either heating or cooling in TiNi shape memory alloys (SMAs). An incomplete cycle on heating (ICH) of shape memory alloy arrested at a temperature between A s and A f induce a kinetic stop slight higher than the arrested temperature in the next complete transformation cycle. An incomplete cycle on cooling of a shape memory alloy arrested at a temperature between M s and M f induce an increase of the transformation heat of the reverse transformation with a decrease in the arrested temperature in the following heating for a sample without R-phase transformation. And for a sample with R-phase transformation, when the stop temperature arrested in the temperature range between R f and M s, the heat flow detected upon following heating only shows one endothermic peak. With decreasing arrested temperature T s to the temperature range between M s and M f, two endothermic peaks can be found upon the following heating. With decreasing arrested temperature T s the transformation heat of the first peak decreases and that of the second peak increases.

Mechanical and shape memory behavior of composites with shape memory polymer

Abstract Shape memory polymers (SMPs) are playing a prominent role for biomedical, self-repairing and smart materials. Among various SMPs, shape memory polyurethanes (PUs) are receiving much attention for their easy control of glass transition temperature (Tg) around the room temperature and excellent shape memory effect even at the room temperature. In this paper, the glass fiber reinforced PUs were developed for the improvement of the mechanical weakness of PUs bulk and for wider practical engineering uses. The specimens with different fiber weight fractions were fabricated and their mechanical behavior and shape memory effect were investigated. As a result, the tensile strength and the resistance against mechanical and thermal mechanical cycle loading in the developed materials increased due to the role of reinforcement fiber. It was shown there is an optimum fiber weight fraction between 10 and 20 wt% to have an extremely low residual strain during cyclic loading. Although the shape memory effect of developed glass fiber reinforced shape memory PUs composites was affected by glass fiber weight fraction, it was confirmed that the shape memory effect was kept in the developed composite materials.

Temperature memory effect of a nickel–titanium shape memory alloy

An incomplete transformation cycle induces a kinetic stop in the following complete transformation cycle in shape memory alloys. Therefore, the kinetic stop can be regarded as a memory of the previous arrest temperature. Herein, we show that the temperature memory effect of a nickel–titanium shape memory alloy can be expanded to be operational in a very wide temperature range by prestraining and constraining, which may be exploited for various practical applications.

Memory effect and temperature behavior in spin valves with and without antiferromagnetic subsystems

Temperature behavior and memory effect in standard spin valves (SV) and SVs with synthetic antiferromagnetic (Co/Ru/Co) (SV-SAF) subsystems have been studied. SV-SAFs show much better temperature stability. Memory effect refers to the phenomenon that the exchange bias can be altered at temperatures (TR’s) much lower than the blocking temperature (TB), and these temperatures (TR’s) are imprinted into SVs. The memory effect greatly deteriorates the magnetoresistance behaviors in SV. Our results suggest that the memory effect is caused by a distribution of local blocking temperatures (Tb’s). The magnetization state in the pinned layer is critical in determining the temperature behavior of HE and magnetoresistance. By partially reversing the magnetization in the pinned ferromagnetic (FM) layers, we are able to separate the temperature dependencies of the local exchange bias (He) associated with regions consisting of different Tb’s. Two features have been observed: (1) the local exchange bias (He) with a narrow Tb distribution has a weak temperature dependence; (2) the simple algebraic sum of local He’s nearly reproduce the total HE with the difference between these two quantities representing the domain wall energy in the FM layer. On the other hand, SV-SAFs show strong resistance to memory effects because of two factors; the strong exchange coupling through the Ru layer, and the net magnetic moment of Co/Ru/Co layers in SV-SAF being close to zero. The former makes the two SV-SAF FM layers behave coherently, while the latter makes the interaction between the SV-SAF and the external field negligibly small.

Studies of the maximum temperature memory effect decay during seismoacoustic emission in sedimentary rocks: B. Zogala, W. M. Zuberek & R. Dubiel, Publications — Institute of Geophysics, Polish Academy of Sciences, series, M, M-19(281), 1995, pp 245–254

Studies of the maximum temperature memory effect decay during seismoacoustic emission in sedimentary rocks: B. Zogala, W. M. Zuberek & R. Dubiel, Publications — Institute of Geophysics, Polish Academy of Sciences, series, M, M-19(281), 1995, pp 245–254

Predictions of a Thermoviscoelastic Constitutive Equation for Specific Volume Relaxation in the Glass Transition Region

Relaxation in the glass transition region is very important to the understanding of the mechanical properties of polymers. Both (i) traditional viscoelastic behavior resulting from application of a mechanical stress or strain and (ii) volume relaxation due to the temperature or pressure change. Structural relaxation near the glass transition region has mostly been probed via isothermal volume recovery after a step change in temperature. Key features of the isothermal volume recovery are well known and include (i) nonlinearity of the kinetics in terms of the magnitude of the initial departure from equilibrium, (ii) asymmetry of the relaxational behavior with respect to the sign of the temperature perturbation and (iii) memory effects related to the thermal history and physical aging.

Stochastic studies of aging and mortality in multicellular organisms. II. The finite theory

We extend the development of a quantitative phenomenological theory of aging rooted in order theory. An organism is represented abstractly by a chain with a finite number of links. Each link corresponds to a possible rate-limiting event or process in senescence. A link is said to break when the corresponding event occurs or the corresponding process goes to completion. The chain is said to break, and the organism subsequently to perish, when the first link breaks, whichever link that might be. Two models are introduced to describe the failure of an arbitrary link. The first requires that a link break only after sustaining a fixed amount of deterioration; the second associates a nonzero probability of failure with each level of wear. The net deterioration of an intact chain is taken, crudely, to correspond to the decline in physiological vitality sustained by an organism during senescence. Failure of an arbitrary link is described in both models by a Markov process. The corresponding mortality rate derived in each instance describes aspects of available empirical data which cannot be accounted for by either the Gompertz or power-law relations. The decline in vitality is shown in both cases to be linear over time intervals of practical interest. The influence of temperature on the senescence of poikilotherms is briefly examined. We describe the effect of temperature both on longevity and the decline in vitality; indicate how substantial discrepancies can arise in the calculation of a macroscopic, effective, activation enthalpy; and lend theoretical support to the existence of temperature-memory effects in senescence.