Damping characteristics of a spray-deposited shape memory alloy beam

The damping characteristics of an Ni–Ti shape memory alloy (SMA) beam are theoretically and experimentally studied with interest in identifying an appropriate damping model for the material. The SMA beam is manufactured by a spray deposition method followed by heat treatment and found to have nanocrystalline structure in which damping capacity is high. The beam is then tested to obtain an impulse response and the frequency response function (FRF). By using the Hilbert transform technique it is shown that damping of the beam is almost amplitude independent in the tested range of displacement. It is also shown from the FRF that the damping of the spray-deposited shape memory alloy beam is well represented by a model including both linear viscous and hysteretic dampings.     

Micropositioning using shape memory alloy actuators

Shape memory alloys (SMA) can be used to generate motion or force in electromechanical devices and micro-machines, although their accuracy is severely limited by their highly nonlinear and hysteretical stimulus-response characteristics. In this work we present some results regarding a nonlinear control method suitable for SMA-based positioning applications. In particular, we show how the hysteresis effects can be compensated using an inverse hysteresis model generated by a neural network, trained using experimental data. The control strategy, experimented on a laboratory SMA actuator, uses the inverse model inserted in a proportional-integral with antiwindup control loop. It is found that neural networks successfully improve the closed-loop response, leading to position accuracies close to a micrometer.     

Effect of enhancement of interface performance on mechanical properties of shape memory alloy hybrid composites

Effect of enhancement of interface performance on mechanical properties of shape memory alloy hybrid composites (SMAHCs) was investigated in this work. Composite laminates without Ni-Ti shape memory alloy (SMA) fibers, with Ni-Ti SMA fibers polished, corroded and modified by silane coupling agent KH550 were taken into comparison to investigate the effect of surface treatments. Surface morphology of Ni-Ti fibers under different treatments were observed with scanning electron microscope. The mechanical performance of specimens without Ni-Ti fibers and with Ni-Ti fibers under different treatments were investigated through tensile, three-point bending and low-velocity experiments. The morphology and micromorphology were observed to study the effect of different surface treatment methods. The conclusion shows that embedded Ni-Ti SMA fibers can enhance the mechanical performance of composite laminates. However, the performance of Ni-Ti SMA fibers was restrained by the poor interface performance. After surface treatments, SMAHCs illustrate better mechanical performance owing to the enhanced interface performance. Among all the surface treatment methods, modification with silane coupling agent KH550 shows the best effect.     

演示记忆合金弹簧的形状记忆效应的实验设计

设计了测试记忆合金弹簧的形状记忆效应的物理实验.描述了实验装置的设计和结构,给出了实验内容的设计和实验方法,包括观察测试记忆合金弹簧的温度-形变记忆效应实验和电流-形变记忆效应实验.根据测量数据,描绘了用该仪器得到的温度-形变曲线和电流-形变曲线.该实验可作为设计性实验在大学物理实验课中开出.     

Temperature evolution in deformed shape memory alloy

Temperature changes during tensile test and simple shear test of TiNi shape memory alloys loaded at various strain rates and at different temperatures have been presented. The temperature changes were measured by recording infrared radiation emitted by the surface of the specimen. It was found that the martensite transformation was accompanied by an increase in temperature while the reversible transformation––temperature decrease.     

Magnetoresistance in ferromagnetic shape memory alloy NiMnFeGa

The magnetoresistance (MR){=[R(H)−R(0)]/R(0)} properties in ferromagnetic shape memory alloy of NiMnFeGa ribbons and single crystals, and NiFeGa ribbons have been investigated. It is found that the NiMnFeGa melt-spun ribbon exhibited GMR effect, arising from the spin-dependent scattering from magnetic inhomogeneities consisting of antiferromagnetically coupled Mn atoms in B2 structure. In the absence of these magnetic inhomogeneities, Heusler alloys seem to show a common linear MR behavior at around 0.8T_C, regardless of sample structures. This may be explained by the s-d model. At low temperatures, conventional AMR behaviors due to the spin-orbital coupling are observed. This is most likely due to the diminished MR from s-d model because of much less spin fluctuation, and is not associated with martensite phase. MR anomaly at intermediate field (ρ_⊥>ρ_||) is also observed in single crystal samples, which may be related to unique features of Heusler alloys.     

Thermal stability and high-temperature shape memory characteristics of Ti–20Zr–10Ta alloy

The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a reversible transformation with the high martensite transformation temperature of 500oC and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.     

Powder metallurgy technology of NiTi shape memory alloy

Powder metallurgy technology was elaborated for consolidation of shape memory NiTi powders. The shape memory alloy was compacted from the prealloyed powder delivered by Memry SA. The powder shows M_s = 10°C and A_s = -34°C as results from DSC measurements. The samples were hot pressed in the as delivered spherical particle's state. The hot compaction was performed in a specially constructed vacuum press, at temperature of 680°C and pressure of 400 MPa. The alloy powder was encapsulated in copper capsules prior to hot pressing to avoid oxidation or carbides formation. The alloy after hot vacuum compaction at 680°C (i.e. within the B2 NiTi stability range) has shown similar transformation range as the powder. The porosity of samples compacted in the as delivered state was only 1%. The samples tested in compression up to ε = 0.06 have shown partial superelastic effect due to martensitic reversible transform- ation which started at the stress above 300 MPa and returned back to ε = 0.015 after unloading. They have shown also a high ultimate compression strength of 1600 MPa. Measurements of the samples temperature changes during the process allowed to detect the temperature increase above 12°C for the strain rate 10^-2 s^-1 accompanied the exothermic martensite transformation during loading and the temperature decrease related to the reverse endothermic transformation during unloading.     

Thermal stability and high-temperature shape memory characteristics of Ti-20Zr-10Ta alloyThermal stability and high-temperature shape memory characteristics of Ti-20Zr-10Ta alloy

The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti-20Zr- lOTa high temperature shape memory alloy were investigated. The Ti-20Zr-10Ta alloy exhibited a reversible transforma- tion with the high martensite transformation temperature of 500 ~C and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.     

Neutron-irradiation-induced shape memory effect in a TiNi alloy

The recovery of inelastic strains in Ti-Ni alloy samples irradiated in a nuclear reactor under isothermal conditions was studied. Before irradiation, the cylindrical samples were compressed to a residual strain of 3–6% in the martenstici state at room temperature. The samples were irradiated at a temperature of 45°C, which does not exceed the temperature of the onset of the reverse martensitic transformation A _S . Irradiation with a fastneutron fluence of 5 × 10²⁰ cm^?2 is established to result in the recovery of the residual strain. The value of the recoverable strain is comparable to that observed under the conditions of the shape memory effect on heating of the deformed alloy and even somewhat exceeds it. The obtained data show that neutron irradiation can induce the shape-memory effect in the TiNi alloy. This is due to a decrease in the temperatures of the martensitic transformations under irradiation.     

石墨颗粒/CuAlMn形状记忆合金复合材料中的位错内耗峰

利用渗流技术制备出了以石墨颗粒为阻尼增强相、以Cu-11.9Al-2.5Mn(wt%)形状记忆合金为基体的复合材料，对该合金的内耗行为进行了研究. 在淬火态样品的内耗-温度曲线上观察到两个内耗峰，分别位于240 ℃和370 ℃附近. 对其中低温峰的变化规律和机理进行了研究. 实验发现，低温峰仅在复合材料中出现，峰位与频率无关，峰高随频率升高而上升；随升温速率增加，峰高增加，峰位移向高温；随石墨颗粒体积分数增加，峰高增加；经多次热循环后该内耗峰消失. 由以上特征和微观观察，可以证明该峰起因于外加交变应力与位错的相互作用.     

石墨颗粒／CuAIMn形状记忆合金复合材料中的位错内耗峰

利用渗流技术制备出了以石墨颗粒为阻尼增强相、以Cu-11．9A1-2．5Mn（wt％）形状记忆合金为基体的复合材料，对该合金的内耗行为进行了研究．在淬火态样品的内耗-温度曲线上观察到两个内耗峰，分别位于240℃和370℃附近．对其中低温峰的变化规律和机理进行了研究．实验发现，低温峰仅在复合材料中出现，峰位与频率无关，峰高随频率升高而上升；随升温速率增加，峰高增加，峰位移向高温；随石墨颗粒体积分数增加，峰高增加；经多次热循环后该内耗峰消失．由以上特征和微观观察，可以证明该峰起因于外加交变应力与位错的相互作用．     

Confining concrete cylinders using shape memory alloy wires

This study proposed a new method to confine concrete cylinders or reinforced concrete columns using martensitic, Ti-49.7Ni (at %), or austenitic, Ti-50.3Ni (at %), shape-memory-alloy wires. Prestrained martensitic SMA wire was used to wrap a concrete cylinder and, then, was heated by a heating jacket. In the process, confining stress was developed around the cylinder by the SMA wire due to shape memory effect, which can increase the strength and ductility of the cylinder under axial compressive load. For austenitic shape memory wires, some prestraining was introduced in the wires during wrapping concrete cylinders on which post-tensioning stress was generated. In this study, 1.0 mm diameter of martensitic and austenitic SMA wire was used for confinement. Recovery tests were conducted for the martensitic and the austenitic shape memory wires to determine the recovery stress and superelastic behavior, respectively. The confinement by martensitic shape memory wires had increased the strength slightly and the ductility substantially. However, the austenitic shape memory wires only increased the ductility because the imposed prestress was too small. This study showed the potential of the proposed method to retrofit reinforced concrete columns using shape memory wires to protect themselves from earthquakes.     

冲击诱发NiTi形状记忆合金相变行为研究

NiTi形状记忆合金的高应变动态响应特性在军事、航空等领域具有重要应用.为研究NiTi合金在动态力学诱导下的相变行为,在不同温区不同冲击速率下,通过轻气炮装置对NiTi合金进行了动态加载实验.利用差示扫描量热仪(DSC),综合物性测量系统分析了冲击波残余效应对NiTi合金相变行为的影响.研究发现:受冲击的样品在第一次DSC热循环中观察到了三个马氏体吸热峰,表现为三步逆马氏体相变,而在第二次热循环中其中两个应力诱发马氏体吸热峰因变形恢复消失.形成两个应力诱发马氏体吸热峰的原因可能是晶粒内部与晶界处的相变过程不同步.受冲击后样品DSC放热峰上出现了一小肩峰,表明可能因中间相(R相)的出现而发生了两步相变,结合电阻测量曲线进一步确认R相的存在,且发现奥氏体相向R相转变以及R相向马氏体相转变这两种相变过程在某一温度范围内可同时进行.同时,文中也具体讨论了不同的冲击加载条件对相变过程的影响.     

Mechanomagnetic spectroscopy of polycrystalline Ni-Fe-Ga-Co ferromagnetic shape memory alloy

Elastic, anelastic, and magnetoelastic properties of polycrystalline Ni-Fe-Ga-Co ferromagnetic shape memory alloy have been studied by means of mechanomagnetic spectroscopy under thermal cycling in the temperature range from 80 to 300 K. The data obtained point to the presence of reversible thermally induced modifications of martensitic and magnetic domain structures in the alloy studied.     

飞秒激光烧蚀镍钛形状记忆合金的蚀除机理

结合双温模型的分子动力学模拟方法,研究了飞秒激光脉冲辐照B2结构镍钛合金时烧蚀阈值附近的靶材蚀除机制,数值模拟了中心波长为800nm,脉宽为100fs,能量密度为25~50mJ/cm2的激光与90nm厚B2结构镍钛合金薄膜相互作用过程。确定了脉宽为100fs的脉冲激光与镍钛形状记忆合金相互作用的烧蚀阈值,发现烧蚀阈值条件下,靶材的蚀除机制是单纯基于应力作用的机械破碎;烧蚀阈值附近,未蚀除靶材受热影响发生无序化相变的区域较小,且随激光能量密度的降低而减小。提高激光功率密度,烧蚀同时呈现热机械蚀除和机械破碎机制。     

飞秒激光烧蚀镍钛形状记忆合金的蚀除机理

结合双温模型的分子动力学模拟方法,研究了飞秒激光脉冲辐照B2结构镍钛合金时烧蚀阈值附近的靶材蚀除机制,数值模拟了中心波长为800 nm,脉宽为100 fs,能量密度为25~50 mJ/cm2的激光与90 nm厚B2结构镍钛合金薄膜相互作用过程。确定了脉宽为100 fs的脉冲激光与镍钛形状记忆合金相互作用的烧蚀阈值,发现烧蚀阈值条件下,靶材的蚀除机制是单纯基于应力作用的机械破碎;烧蚀阈值附近,未蚀除靶材受热影响发生无序化相变的区域较小,且随激光能量密度的降低而减小。 提高激光功率密度,烧蚀同时呈现热机械蚀除和机械破碎机制。     

Laser welding of thin foil nickel-titanium shape memory alloy

In this study, two L27 Taguchi experiments were carried out to study the effect of fibre laser welding parameters and their interactions upon the weld bead aspect ratio of nickel-titanium thin foil. The optimum parameters to produce full penetrated weld with the largest aspect ratio and desirable microstructure were successfully obtained by the Taguchi experimental design. The corrosion property of the optimized NiTi weld in Hank’s solution at 37.5 °C was studied and compared with the as-received NiTi. To improve the corrosion properties of the weld, the effect of post-weld-heat-treatments ranging from 573 to 1173 K was investigated. The corrosion properties, surface morphology, microstructure and Ti/Ni ratio of the heat-treated NiTi weld were analysed. It was found that a post-weld heat treatment at 573 K for 1 h provided the best pitting corrosion resistance at the weld zone.     

Investigation of shape memory characteristics and production of HfZrTiFeMnSi high entropy alloy by mechanical alloying method

High entropy alloy (HEA) with shape memory effect (SME) has been the subject of great interest for the past few decades. However, with the increased demands for new materials for high thermal applications, the research activities on the multi elemental high entropy shape memory alloys (HESMA) have been increased by many folds recently. The nano crystalline HEA powder with shape memory effect developed in this study, HfZrTiFeMnSi, was produced by mechanical alloying (MA) for the first time. In this method equiatomic ratio of Hf, Zr, Ti, Fe, Mn, and Si were mixed together and milled by MA process for 100 h. The powder formed was of amorphous in nature. Elemental mapping of the powder from SEM-EDS revealed homogeneity of the alloying elements confirming successful fabrication of HfZrTiFeMnSi HEA powder. The DSC studies from ambient to 500 °C of the annealed alloy powders showed reversible austenitic to martensitic (A↔M) transformations. The A↔M transformation hysteresis seemed to vary with the milling time and annealing temperature. The enthalpy values, ΔH, for the transformation were calculated from the DSC plots using tangent method for peak area calculation. Regardless of the annealing temperature, the thermal analysis revealed that the ΔH, equilibrium temperature (T₀), and crystallization temperature values decreased with the increasing milling time.     

A strain-fiber actuator by use of shape memory alloy spring

A strain-fiber actuator by use of shape memory alloy spring is proposed and experimentally investigated. The shape memory alloy actuator with a diameter of 0.3 mm and length of 2 mm was driven by a DC power supply of 7 V to persist for 5 s. The deformation and the strain ratio were found to be 60 μm and 3%, respectively. To apply the actuator to strain a fiber Bragg grating, we obtained a tunable spectrum width of 50 nm around the wavelength of 1550 nm for optical communication.