Shape Memory Effect

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, γ2, and α phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of γ2 phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into γ2 phase and equilibrium α phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, γ2, and α phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.

This special issue addresses the possible connections and mutual benefits of examining together two analytic concepts – memory and periphery. These concepts receive much attention in various scholarly discussions, yet they have done so rather independently from each other. The potential applications and utilities of combining memory and periphery and the epistemic insights they provide for various disciplins are presented in the different contributions to this issue.

Thermomechanical and functional properties of shape memory polymer (SMP) have been presented. Taking advantages from high quality testing machine and infrared camera, mechanical characteristics and temperature changes of the shape memory polyurethane specimens subjected to tension and simple shear processes were recorded, worked out, completed and discussed. The material is said to demonstrate a shape memory properties since it can

A 10 bit opamp-sharing pipeline analog-to-digital converter (ADC) using a novel mirror telescopic operational amplifiers (opamp) with dual nmos differential inputs is presented. Reduction of power and area is achieved by completely merging the front-end sample-and-hold amplifier (SHA) into the first multiplying digital-to-analog converter (MDAC) using the proposed opamp. Transistors in the opamp are always biased in saturation to avoid increase of settling time due to opamp turn-on delays. The design targets 0.18um CMOS process for operation, at 200MS/s from a 1.8V supply. The simulation results show the SNDR and SFDR of 59.45dB and 68.69dB, respectively, and the power consumption of 35.04mW is achieved.

and recovery, and drying of materials, signifi cantly increase the process complexity and increase the process time. Herein, we report an ultrafast, room-temperature process for manufacturing auxetic PU foams that can be completed in as little as several seconds. We also illustrate the fundamentals that enable this facile manufacturing. The fabricated auxetic foams exhibit a nearly constant negative Poisson's ratio over a large range of strain. This technology overcomes the aforemen-tioned fundamental materials properties constraints to enable robust, consistent, highly effi cient, and potentially large-scale manufacturing of the auxetic PU foams with excellent properties. The process is also environmentally benign, making use of carbon dioxide as the processing agent that is completely removed from the product at the end of the process. The process leverages on a fundamental understanding of the auxetic conversion mechanism of PU foam in our previous study, [ 20 ] and makes ingenious use of carbon dioxide to reduce the polymer glass transition temperature to expedite the stress relaxation of a particular phase in the multicomponent mul-tiphase PU foam that dictate the auxetic conversion process. PU foams suitable for auxetic manufacture normally consisted of two domains: An elastic, rubbery PU matrix domain and glassy styrene acrylonitrile copolymer (SAN) particles reinforcement phase that improves the loading bearing capability of the foams. The rubber domain provides the necessary deformation capability for auxetic conversion. The auxetic structure fi xa-tion is accomplished by stress-induced deformation and relaxation of the viscoelastic rubbery SAN copolymer particles at processing temperature, and return to the glassy state during the cooling stage of the manufacturing. The deformed glassy SAN particles act as physical cross-links to fi x the auxetic structure. [ 20 ]

The phase transitions and magnetoresistance in polycrystalline ferromagnetic Ni50Mn50-xInx (15<=x<=16.2) Heusler alloys were studied through ac susceptibility, magnetization, thermal expansion, and resistivity measurements in the temperature interval of 5-400 K. The temperatures of the martensitic transformations were found to be strongly dependent on In concentration and on the strength of the applied external magnetic field. We observed large magnetoresistance (MR)

We conducted the measurement of the hardness-depth relationship of NiTi shape memory alloy with a sharp Berkovich indenter. Different from most ductile metals, NiTi reacts to the mechanical load of indentation through phase transition underneath the indentation tip. We found that the hardness decreases rapidly with the increase of the indentation depth and eventually approaches a constant. To understand the depth dependency, we performed energy analysis involving the bulk and the interface energies of the transformation zone. We derived the hardness-depth relationship which well explains the experimental results. The finding is useful in hardness measurement of materials involving solid-state phase transitions.

Two constitutive models representative of two well-known modeling techniques for superelastic shape-memory wires are reviewed. The first model has been proposed by Kim and Aberayatne in the framework of finite thermo-elasticity with non-convex energy [1]. In the present paper this model has been modified in order to take into account the difference between elastic moduli of austenite and martensite and to introduce the isothermal approximation proposed in [1]. The second model has been developed by Auricchio et. al. within the theory of irreversible thermodynamics with internal variables [2]. Both models are temperature and strain rate dependent and they take into account thermal effects. The focus in this paper is on investigating how the two models compare with experimental data obtained from testing superelastic NiTi wires used in the design of a prototypal anti-seismic device [3,4]. After model calibration and numerical implementation, numerical simulations based on the two models are compared with data obtained from uniaxial tensile tests performed at two different temperatures and various strain rates.