PASSIVE DAMPING AUGMENTATION OF A VIBRATING BEAM USING PSEUDOELASTIC SHAPE MEMORY ALLOY WIRES

This paper examines the effectiveness of pseudoelastic shape memory alloy (SMA) wires for passive damping of flexural vibrations of a clamped-free beam with a tip mass. A finite-element model of the system is developed and validated with experimental results. The SMA behavior is modelled using amplitude-dependent complex modulus. Numerical simulations indicate that the damping introduced by the SMA wires will increase for higher excitation-force amplitudes that produce higher strain levels in the SMA wires. Increasing the wire cross-section area provides more damping at low force-excitation amplitudes, but reduced damping at higher amplitudes. The angle between the beam and the SMA wires is an influential parameter, and a value in the 10-20° range was found to introduce maximum damping. The underlying physical mechanisms are examined in detail. System damping depends only mildly on the SMA wire length, and is unaffected by the tip mass.     

INDIRECT INTELLIGENT SLIDING MODE CONTROL OF A SHAPE MEMORY ALLOY ACTUATED FLEXIBLE BEAM USING HYSTERETIC RECURRENT NEURAL NETWORKS

This paper introduces an indirect intelligent sliding mode controller (IISMC) for shape memory alloy (SMA) actuators, specifically a flexible beam deflected by a single offset SMA tendon. The controller manipulates applied voltage, which alters SMA tendon temperature to track reference bending angles. A hysteretic recurrent neural network (HRNN) captures the nonlinear, hysteretic relationship between SMA temperature and bending angle. The variable structure control strategy provides robustness to model uncertainties and parameter variations, while effectively compensating for system nonlinearities, achieving superior tracking compared to an optimized PI controller.     

Transfer bonding technology for batch fabrication of SMA microactuators

Currently, the broad market introduction of shape memory alloy (SMA) microactuators and sensors is hampered by technological barriers, since batch fabrication methods common to electronics industry are not available. The present study intends to overcome these barriers by introducing a wafer scale transfer process that allows the selective transfer of heat-treated and micromachined shape memory alloy (SMA) film or foil microactuators to randomly selected receiving sites on a target substrate. The technology relies on a temporary adhesive bonding layer between SMA film/foil and an auxiliary substrate, which can be removed by laser ablation. The transfer technology was tested for microactuators of a cold-rolled NiTi foil of 20 μm thickness, which were heat-treated in free-standing condition, then micromachined on an auxiliary substrate of glass, and finally selectively transferred to different target substrates of a polymer. For demonstration, the new technology was used for batch-fabrication of SMA-actuated polymer microvalves.     

Nonlinear dynamics of a rotordynamic nonsmooth shape memory alloy system

This contribution deals with the analysis of a rotordynamic nonsmooth shape memory alloy (SMA) system. The rotor–bearing system is modeled as a Jeffcott rotor with two-degrees of freedom and discontinuous supports. Two different situations are investigated: linear elastic support and shape memory alloy support. Numerical simulations are carried out establishing a comparison between elastic and SMA systems, showing situations where nonlinear effects of SMAs are interesting in dynamical responses avoiding undesirable behaviors. Temperature dependence of SMA response is investigated showing adaptive aspects of this kind of system.     

具有形状记忆效应的新型智能阻尼材料及其热弹性力学性能研究

将传统金属橡胶制备工艺和形状记忆合金材料相结合, 研制了一种新型智能阻尼材料——-记忆合金金属橡胶, 并对其成型工艺、形状记忆效应、热弹性力学性能及参数影响规律进行了试验研究. 研究表明, 作为一种特殊的金属橡胶, 该材料不仅具备普通金属橡胶高阻尼、低密度、孔隙度可控等优点, 同时具备普通金属橡胶所不具备的智能材料特征: 1)良好的单程形状记忆效应, 该材料在大载荷加载后的残余塑性变形可以在升温过程中完全恢复; 2) 弹性模量和损耗因子具有温变特性, 在相变温度区间内弹性模量和损耗因子随温度近似线性变化. 由于同时具备金属橡胶和形状记忆合金两大金属类功能材料的优点, 形状记忆合金金属橡胶成为一种可应用于振动主动控制、 集良好承载能力和阻尼特性于一身、具有结构功能一体化优 势的新型智能阻尼材料.     

A macro-mechanical constitutive model of shape memory alloys

It is of practical interest to establish a precise constitutive model which includes the equations describing the phase transformation behaviors and thermo-mechanical processes of shape memory alloy (SMA). The microscopic mechanism of super elasticity and shape memory effect of SMA is explained based on the concept of shape memory factor defined by the author of this paper. The conventional super elasticity and shape memory effect of SMA are further unified as shape memory effect. Shape memory factor is redefined in order to make clear its physical meaning. A new shape memory evolution equation is developed to predict the phase transformation behaviors of SMA based on the differential relationship between martensitic volume fraction and phase transformation free energy and the results of DSC test. It overcomes the limitations that the previous shape memory evolution equations or phase transformation equations fail to express the influences of the phase transformation peak temperatures on the phase transformation behaviors and the transformation from twinned martensite to detwinned martensite occurring in SMA. A new macro-mechanical constitutive equation is established to predict the thermo-mechanical processes realizing the shape memory effect of SMA from the expression of Gibbs free energy. It is expanded from one-dimension to three-dimension with assuming SMA as isotropic material. All material constants in the new constitutive equation can be determined from macroscopic experiments, which makes it more easily used in practical applications. Supported by the National Natural Science Foundation of China (Grant No. 95505010), the National High Technology Research and Development Program of China (Grant No. 2006AA03Z109), the China Postdoctoral Science Foundation (Grant No. 20080430933), the Open Foundation of Institute of Engineering Mechanics of National Seism Bureau of China (Grant No. 2007B02), and the Harbin Talent Foundation of Scientific and Technical Innovation (Grant No. RC2009QN-017046)     

Development of the Technique for Fabricating Submicron Moire Gratings on Metal Materials Using Focused Ion Beam Milling

A focused gallium ion （Ga＋） beam is used to fabricate micro/submicron spacing gratings on the surface of porous NiTi shape memory alloy （SMA ）. The crossing type of gratings with double-frequency （25001/mm and 50001/mm） using the focused ion beam （FIB） milling are successfully produced in a combination mode or superposition mode. Based on the double-frequency gratings, high-quality scanning electron microscopy （SEM） Moird patterns are obtained to study the micro-scale deformation of porous NiTi SMA. The grating fabrication technique is discussed in detail. The experimental results verify the feasibility of fabricating high frequency grating on metal surface using FIB milling.     

Accurate identification of the frequency response functions for the rotor-bearing-foundation system using the modified pseudo mode shape method

In this paper, an identification technique in the dynamic analyses of rotor-bearing-foundation systems called the pseudo mode shape method (PMSM) was improved in order to enhance the accuracy of the identified dynamic characteristic matrices of its foundation models. Two procedures, namely, phase modification and numerical optimisation, were proposed in the algorithm of PMSM to effectively improve its accuracy. Generally, it is always necessary to build the whole foundation model in studying the dynamics of a rotor system through the finite element analysis method. This is either unfeasible or impractical when the foundation is too complicated. Instead, the PMSM uses the frequency response function (FRF) data of joint positions between the rotor and the foundation to establish the equivalent mass, damping, and stiffness matrices of the foundation without having to build the physical model. However, the accuracy of the obtained system's FRF is still unsatisfactory, especially at those higher modes. In order to demonstrate the effectiveness of the presented methods, a solid foundation was solved for its FRF by using both the original and modified PMSM, as well as the finite element (ANSYS) model for comparisons. The results showed that the accuracy of the obtained FRF was improved remarkably with the modified PMSM based on the results of the ANSYS. In addition, an induction motor resembling a rotor-bearing-foundation system, with its housing treated as the foundation, was taken as an example to verify the algorithm experimentally. The FRF curves at the bearing supports of the rotor (armature) were obtained through modal testing to estimate the above-mentioned equivalent matrices of the housing. The FRF of the housing, which was calculated from the equivalent matrices with the modified PMSM, showed satisfactory consistency with that from the modal testing.     

An optimal process of femtosecond laser cutting of NiTi shape memory alloy for fabrication of miniature devices

The mechanical properties of NiTi shape memory alloy (SMA) components are sensitive to thermal influence during laser machining. To make the femtosecond laser cutting of NiTi material meet the strict fabrication requirements for miniature SMA devices with high precision, complex patterns and minimal heat affected zone (HAZ) along with high throughput, we report an optimal process of sideways-movement path planning in this article. Femtosecond laser processing of NiTi SMA using the fundamental wavelength of 775 nm from a Ti:sapphire laser along with its second and third harmonic irradiations were systematically investigated. We observed that the main impact of ultrashort laser pulse induced air breakdown on materials processing was beam widening. The laser beam at fundamental wavelength suffered less widening than its harmonic wavelengths. Femtosecond laser machining of metals is still basically a thermal mechanism. High ablation rates at higher laser fluences causes significant recast formation, while lower fluences resulted in better cutting quality at the expense of efficiency. The optimal process involving the method of sideways-movement path planning enables recast-free high-precision features at higher laser fluences with better throughput.     

Swept sine testing of rotor-bearing system for damping estimation

Many types of rotating components commonly operate above the first or second critical speed and they are subjected to run-ups and shutdowns frequently. The present study focuses on developing FRF of rotor bearing systems for damping estimation from swept-sine excitation. The principle of active vibration control states that with increase in angular acceleration, the amplitude of vibration due to unbalance will reduce and the FRF envelope will shift towards the right (or higher frequency). The frequency response function (FRF) estimated by tracking filters or Co-Quad analyzers was proved to induce an error into the FRF estimate. Using Fast Fourier Transform (FFT) algorithm and stationary wavelet transform (SWT) decomposition FRF distortion can be reduced. To obtain a theoretical clarity, the shifting of FRF envelope phenomenon is incorporated into conventional FRF expressions and validation is performed with the FRF estimated using the Fourier Transform approach. The half-power bandwidth method is employed to extract damping ratios from the FRF estimates. While deriving half-power points for both types of responses (acceleration and displacement), damping ratio (ζ) is estimated with different approximations like classical definition (neglecting damping ratio of order higher than 2), third order (neglecting damping ratios with order higher than 4) and exact (no assumptions on damping ratio). The use of stationary wavelet transform to denoise the noise corrupted FRF data is explained. Finally, experiments are performed on a test rotor excited with different sweep rates to estimate the damping ratio.     

基于OTDR和SMA原理的分布温度阈值执行器的设计

温度阈值执行器的设计是准分布光纤温度报警系统对温度报警空间定位的关键.本文分析了基于OTDR和SMA设计温度阈值执行器的原理,提出了执行器的物理模型.通过实验测试,从SMA弹簧样品中选出了满足执行器技术要求的记忆弹簧,完成了执行器的机械设计.系统运行表明:执行器能有效运作,能够实现准分布温度报警,并且系统具有接近1.5 m的空间分辨率和低于16 s的响应时间等优良的性能参数.     

Large-deformation analysis in microscopic area using micro-moiré methods with a focused ion beam milling grating

In this study, the focused ion beam (FIB) milling method is applied to fabricate sub-micron grating on TiNi shape memory alloy materials. With self-made FIB milling gratings, scanning electron microscope (SEM) micro-moiré and digital moiré methods are successfully used to measure large deformation of porous TiNi shape memory alloys (SMA) in uni-axial compressive tests. The principles of the SEM micro-moiré method and digital moiré method are introduced, and applied to calculate large strain. The full field deformation around shear bands can be measured precisely. During the investigation, the phenomenon of furcated moiré fringes was found, and a corresponding explanation is given in this paper. The furcated fringes are generated in the locations of combined shear bands where sudden changes of strain occur. Successful results also verify that the FIB milling gratings are suitable for micro-moiré measurement and can generate high quality moiré fringes.     

A shape memory alloy-based tunable phononic crystal beam attached with concentrated masses

Shape memory alloys (SMAs) in phononic crystals (PCs) or metamaterials mostly serve as smart inserts or local resonators to generate tunable bandgaps for other structures. In this letter, we address the method for creating tunable bandgaps in structures made of SMA. Specifically, we consider concentrated masses, realized by steel balls, as attachments on a SMA. To provide a design guideline, we derived the closed-form bandgap formula of the proposed SMA PC beam. As the bandgap order increases, the coefficient of the nth Bragg bandgap width decreases. In addition, the practical final beam enlarges bandgap edges than ideally infinite PCs or metamaterials. Our experimental results on the PC beam with different sizes of the steel ball arrays agree with the analytical predictions of the bandgap behaviors. With the bandgaps formed by the steel balls and the shape memory effect, wide tunability of the bandgaps are achieved on the SMA beam.     

Prediction of uncertain frequency response function bounds using polynomial chaos expansion

A probabilistic method is developed to predict the uncertainty bounds on Frequency Response Functions (FRFs) developed from Finite Element models. A non-intrusive Polynomial Chaos Expansion (PCE) method is used to predict uncertainty regression models of the various parameters that make up a curvefit of the FRF: natural frequencies, damping ratios, complex amplitudes, mass and stiffness residuals, by making use of an efficient Latin Hypercube technique. These uncertainty models are then combined to efficiently determine PDFs of the parameters and also the uncertainty bounds of the FRFs. The approach is demonstrated using two examples; a simple beam containing uncertainty in Young's Modulus, and a full-scale aircraft composite wing model containing uncertainties in both Young's modulus and the shear modulus. The results were compared with Monte Carlo Simulation (MCS) and it was found that the parameter PDFs and FRF error bounds obtained using a 2nd-order PCE model agreed very well whilst requiring significantly less computation.     

Pitch-variable transmission-type bulk gratings driven by shape memory alloy actuator

This paper describes a novel pitch-variable transmission-type bulk grating fabricated by silicon micromachining technology driven by a shape memory alloy (SMA) actuator. The grating is specially designed to change the pitch easily with a small force and assured moderate stress by finite element method. Using deep reactive ion etching (deep-RIE) technology, the grating has a high aspect ratio more than 10. In the diffraction experiment, more than 10% extension ratio has been obtained. The SMA actuator has been installed to the grating. Due to the two-way shape memory effect, the translation mechanism is simple and is easily controlled.     

Study on the Compatibility of SMA and Composite Materials by Holographic Interferometry

With the help of holographic interferometry a study is conducted on the compatibility of SMA (shape memory alloy) and epoxy resin composite material. The paper gives experiment results and analysis which show that after coupling SMA with the composite material, the flexural rigidity of composite material is somewhat reinforced. Under certain conditions, SMA and the epoxy resin composite material are compatible.     

Study on the Compatibility of SMA and Composite Materials by Holographic Interferometry

With the help of holographic interferometry a study is conducted on the compatibility of SMA (shape memory alloy) and epoxy resin composite material. The paper gives experiment results and analysis which show that after coupling SMA with the composite material, the flexural rigidity of composite material is somewhat reinforced. Under certain conditions, SMA and the epoxy resin composite material are compatible.     

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.     

Reversible and irreversible martensitic transformations in Fe-Pd and Fe-Pd-Co alloys

Ferromagnetic Fe-Pd shape memory alloys (SMA) undergo a martensitic phase transformation during cooling from a parent FCC phase to a tetragonal FCT martensite. This transformation is thermoelastic and reversible giving rise to the shape memory effect. On further cooling an irreversible FCT to BCT transformation occurs that makes impossible the memory effect. Nevertheless, the transformation from reversible to irreversible phase has been not complete since a volume fraction of reversible phase in the alloy is retained even after cooling below the temperature of appearance of the irreversible phase. The addition of Co lowers the temperature of the reversible and irreversible phase transformations but also reduces the amount of transformed irreversible martensite after cooling to 10 K.     

Modelling the spindle–holder taper joint in machine tools: A tapered zero-thickness finite element method

This study presents a tapered zero-thickness finite element model together with its parameter identification method for modelling the spindle–holder taper joint in machine tools. In the presented model, the spindle and the holder are modelled as solid elements and the taper joint is modelled as a tapered zero-thickness finite element with stiffness and damping but without mass or thickness. The proposed model considers not only the coupling of adjacent degrees of freedom but also the radial, tangential and axial effects of the spindle–holder taper joint. Based on the inverse relationship between the dynamic matrix and frequency response function matrix of a multi-degree-of-freedom system, this study proposes a combined analytical–experimental method to identify the stiffness matrix and damping coefficient of the proposed tapered zero-thickness finite element. The method extracts those parameters from FRFs of an entire specimen that contains only the spindle–holder taper joint. The simulated FRF obtained from the proposed model matches the experimental FRF quite well, which indicates that the presented method provides high accuracy and is easy to implement in modelling the spindle–holder taper joint.