Changes In Vibrational Frequencies Research Articles

Electronic-level insight into the weak interactions of ion pairs in acetate anion-based ionic liquids

The weak interactions in ion pairs of acetate anion-based ionic liquids (ILs) were investigated by dispersion-corrected density functional theory (DFT) calculations, where the structural parameters and vibrational frequency changes of ion pairs and isolated ions were systematically analyzed. Four kinds of stable configurations for ILs 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) and 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) were determined by calculating the interaction energies of different ion pairs. The essence of weak interactions between ion pairs was qualitatively and quantitatively characterized by the electrostatic potential (ESP) of anions and cations, natural bond orbital (NBO), atoms in molecules (AIM), and Generalized Kohn-Sham energy decomposition analysis (GKS-EDA). The results indicated that the red-shifted hydrogen bond (H-bond) of C1-H2⋯O contributed the most to the stability of ion pairs. For the different stable ion pairs, the H-bond interactions formed by acetate anion ([OAc]−) with H protons on the imidazolium ring and side chain were separately divided into medium and weak H-bond, showing partly covalent and noncovalent nature. GKS-EDA results revealed that the interactions of ion pairs were mainly electrostatic dominant, charge transfer and orbital overlap contributions were also significant, which were in accordance with the ESP, NBO, and AIM analyses results. Hopefully, this study could offer an insight into weak interactions principle of ILs and provide a theoretical basis for predicting their physicochemical properties.

Understanding the interactions between hydrogen-bonded complexes of xylose and water: Quantum Chemical Investigation

Hydrogen-bonded complexes between xylose and water, modelled by xylofuranose…H2O complexes were explored employing ab initio quantum chemical framework. The Moller–Plesset second-order perturbation theory (MP2) in conjugation with aug-cc-pVDZ basis set, is used for investigating the H-bonding interactions. The complete basis set limit interaction energies for α-and β-xylofuranose and xylopyranose water complexes were calculated at MP2 level. It is observed that the addition of water molecule does not change the conformational structure of xylose moieties. Further water is found to interact with xylose mainly through the O atom present in a ring and its neighboring OH group. Energy decomposition analysis by LMO-EDA approach indicates that the electrostatic and exchange interactions are the two largest contributing terms to the total interaction energy for bonding between Xylose and water. The nature of interaction between xylose and water is investigated by means of MP2/CBS interaction energies, energy decomposition analysis, change in vibrational frequencies and electron density critical points. It was found that xylofuranose has more affinity towards water than xylopyranose form.

Transverse horizontal vibrations of contact network wires for monitoring their tension during operation

The paper describes the structure of a hardware and software complex for monitoring and diagnostics of the contact network, provides information about the hardware blocks of the complex, considers its implementation in Matlab/Simulink, describes the regularities of change of vibration frequency under different values of tension and the linear mass of wires.

New Kind of Polymer Materials Based on Selected Complexing Star-Shaped Polyethers.

In today’s analytical trends, there is an ever-increasing importance of polymeric materials for low molecular weight compounds including amines and drugs because they can act as carriers or capture amines or drugs. The use of this type of materials will allow the development of modern materials for the chromatographic column beds and the substrates of selective sensors. Moreover, these kinds of materials could be used as a drug carrier. Therefore, the aim of this study is presenting the synthesis and complexing properties of star-shaped oxiranes as a new sensor for the selective complexation of low molecular weight compounds. Propylene oxide and selected oxirane monomers with carbazolyl in the substituent were selected as the monomers in this case and tetrahydrofuran as its solvent. The obtained polymer structures were characterized using the MALDI-TOF. It was found that in the initiation step potassium hydride deprotonates the monomer molecule and takes also part in the nucleophilic substitution. The resulting polymeric material preferably cross-linked with selected di-oxiranes (1,2,7,8-diepoksyoktan in respect ratio 3:1 according to active center) was then used as a stationary phase in the column and thin layer chromatography for amine separation and identification. Sorption ability of the resulting deposits was determined using a quartz microbalance (QCMB). The study was carried out in stationary mode and flow cells to simulate actual operating phase conditions. Based on changes in electrode vibration frequency, the maximum amount of adsorbed analyte and the best conditions for its sorption were determined.

Fluidization of fine powder assisted by vertical vibration in fluidized bed reactor

This study examined the fluidization phenomenon using vertical vibration for fine powder in a mechanical vertical vibration for fluidized bed reactor. The fine powder used belongs to the Geldart group C with a mean powder size of 2.25 µm. It was verified that channeling and agglomeration phenomena appeared with a fluidization method without vibration of fine powders belonging to the group C. To keep fluidization phenomenon of the agglomerating fine powder superior, a smooth fluidization condition was made by giving vertical vibration function and removing cohesion between particles. To verify the smooth fluidization condition of the fine powder, changes in the bed height to diameter (H/D) ratio of the fluidized bed reactor, pressure drop due to changes of vibration frequency with superficial gas velocity, minimum fluidization velocity, and changing characteristics of bed expansion ratio were investigated experimentally. This study examined pressure drops from H/D variable of values 1 and 2, minimum fluidization velocity, and bed expansion ratios at 0 to 60 Hz of vibration frequency. There is a trend that as vibration frequency increases, the pressure drop is stabilized, minimum fluidization velocity decreases, and the bed expansion ratio increases.

Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements

Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnäsite [(Ce,La)FCO3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. Here, the adsorption of octyl hydroxamic acid onto bastnäsite was measured using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnäsite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnäsite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnäsite than with a common gangue mineral, calcite (CaCO3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength of metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores.

Constructing Metal Arch Nanobridges Utilizing a Photothermal‐Induced Nanobonding Technique

AbstractConstruction of multilayered arch nanobridges and nanocantilever structures consisting of silver nanowires using a photothermal‐induced nanobonding technique is demonstrated. The fabricated nanobridges are of different height (300 nm to 20 µm) and span (25–70 µm). Their current–voltage characteristic curves indicate superior electrical connection between the metal nanowires and the abutments (gold thin film). Moreover, super mechanical strength of these arch nanobridges and nanocantilevers is demonstrated by putting gold nanoplates (a few tens of nm thick, a few tens of µm in diameter, and a maximum weight of 3 pN—about 20 times heavier than the silver nanowire of same length) on top of these nanostructures. The multilayered arch nanobridges demonstrate their potential applicability as short‐circuit‐free multipronged electronic connections in nanoelectronic devices. Furthermore, by recording the change in vibration frequency due to proximity of foreign contamination, these nanobridges and the nanocantilevers can be utilized to identify them; that is, these nanostructures can be used as biological sensors to detect viruses, bacteria, and other pathogens.

Experimental identification of the fluid-elastic coupling forces on a flexible tube within a rigid square bundle subjected to single-phase cross-flow

The importance of fluid-elastic coupling forces in tube bundle vibrations is well documented and can hardly be over-emphasized, in view of their damaging potential. Even when adequate tube supports are provided to suppress fluid-elastic instabilities, the flow-coupling forces still affect the dynamical tube responses and remain a significant issue, in particular concerning the vibro-impact motions of tubes assembled using clearance supports. Therefore, the need remains for more advanced models of fluid-elastic coupling, as well as for experimental flow-coupling coefficients to feed and validate such models. In this work, we report an extensive series of experiments performed at CEA-Saclay leading to the identification of stiffness and damping fluid-elastic coefficients, for a 3×5 square tube bundle (D = 30 mm, P/D = 1.5) subjected to single-phase transverse flow, in a water test-loop. The bundle is rigid, except for the central tube which is mounted on a flexible suspension (two parallel steel blades) allowing for translation motions of the tube in the lift direction. The system is thus single-degree of freedom, allowing fluid-elastic instability to arise through a negative damping mechanism. The flow-coupling stiffness and damping coefficients, Kf(Vr) and Cf(Vr), are experimentally identified as functions of the reduced velocity Vr. The maximum value of the Reynolds number ranged from 105 to 2.16 105 (based on the maximum pitch velocity), according to the tested configuration. Identification is achieved on the basis of changes in tube vibration frequency and reduced damping as a function of flow velocity, assuming a constant fluid added mass. In the present experiments, coefficient identification is performed well beyond the instability boundary, by using active control, thereafter allowing exploration of a significant range of flow velocity. The modal frequency and the modal mass of the system are respectively modified by changing the tube suspension stiffness, and/or by adding a mass to the system. We can thus assert how the fluid-elastic coefficients change, for this configuration, with these two system parameters, all other parameters being kept constant. The results obtained from the configurations tested suggest that formulations for coefficient reduction may be improved, in order to better collapse the identified data.

Generalized two-dimensional correlation NIR spectroscopy analysis of the structures on n-propanol and n-butanol

The hydrogen bond (H-bond) is one of the most important intra- and inter molecular attraction in chemistry, while the hydroxyl is one of the chemical groups that forms H-bond most easily. Therefore, a detailed understanding of the hydroxyl group is essential to a fundamental understanding of the H-bond. In this paper, the molecular structures especially the H-bond were investigated through the near infrared spectra (NIR) of n-propanol and n-butanol over a temperature range of 36–76 °C (or 36–79 °C) using two-dimensional correlation spectroscopy (2D-Correlation) techniques. The following results were drawned:1) the change of the hydroxyl vibrational frequency is caused by the breakage of H-bonds as the temperature increases, the vibrational frequencies of the H-bonds and free hydroxyl remain unchanged. However, the spectral peak positions shifted as the changed of H-bonds and free hydroxyl's composition. 2) when the temperature rose, the absorption of the free hydroxyl vibration in the first overtone region increased faster than H-bonded hydroxyl was reduced, which means that the frequency of H-bonded hydroxyl shifted to higher frequency before breaking. However, in the combination vibration region where both free hydroxyl and H-bonded hydroxyl overlapped, the situation is just the opposite; that is, the change of H-bonded hydroxyl is faster than in free hydroxyl. This difference may be related to the symmetry of hydroxyl's combination vibration. 3) With the increased temperature, the combination absorption will be partially converted to overtone vibration absorption, and the combination vibration absorption of n-propanol will be changed more easily into the first overtone absorption than is the case for n-butanol due to poor symmetry. 4) Principal component analysis (PCA) leads the authors to propose three possible states of hydroxyl bonding: free (non-H-bonding) hydroxyl, inter-hydroxyl group binding (through one or two H-bonds), and a weak force bonding (less bond energy than H-bonding) between the hydroxyl and alkyl groups on different molecules.

УСТАНОВКА ДЛЯ ИСПЫТАНИЙ ОБРАЗЦОВ ПОКРЫТИЙ ПРИ ПЕРЕМЕННЫХ НАГРУЗКАХ

While in operation, the parts with the applied coatings often work under variable loads, which affects the service life of the products. Many papers deal with the study of fatigue properties of such products, however, the study of the influence of variable loads on the structure and properties of the coatings has a fragmented nature. As the determination of fatigue characteristics of samples with the applied coatings is still important, the goal of this paper is to develop the design of the plant for fatigue tests and the technique of testing the samples with coatings under the variable loads. To develop the technique of fatigue tests, the authors created a unique design plant. When developing the plant, the authors considered the fact that the loading of a sample should be regular that the base and the substrate materials will experience stresses constant along the full length of a sample. Using the analytical solution of the strength task, the authors developed the technique of determining the stresses in a coating and a substrate. To prove the appropriateness of using the suggested technique, the numerical methods were used. For this purpose, using the Comsol Multiphysics software in a 2-D setup, the authors were solving the task of determining stresses in a sample consisted of two layers of the materials. In the result of the study, the authors developed the design of an experimental plant for testing samples with coatings with the maximum tensile force of 5000 N and the possibility of smooth change of vibrational frequency. The authors developed and tested the technique of testing samples with coatings without separation of a coating from a substrate. The study showed that the application of the described technique is reasonable if the thickness of a coating is not more than 7 % of the thickness of a substrate.

Study the Effect of Using Different Bearing Types on the Performance of Evaporative Cooler

An investigation of performance response of two types of bearings such as Cylindrical Roller Bearing and bush bearing on evaporative cooler driven by DC motor of 1500 r.p.m, through studying many parameters like vibration response, temperature raise, humidity, sound level and total performance. high quality 3D positions X, Y and Z, vibration sensors type (ADXL335 accelerometers) with Arduino mega 2560 that interfaced with Lab-View program were used to measure changes in vibration amplitude and frequency. Two temperature sensors of type (LM35) were used to investigate the temperature raise in the bearings also with Arduino mega 2560 that interfaced with Lab-View program. For humidity a sensor of type DHT22 was used, also, a portable device was used to measure electricity consumption, rotary speed and sound level in the bearings of evaporative cooler. By replacing bearings all the parameters above wear measured then a comparison between them were made to find the best performance and operation of these bearings. The obtained results from the experimental work have clarified and explained by tables and figures. It has been found that the vibration of evaporative cooler in X, Y and Z-directions increased by using two cylindrical roller bearings than using two of bush bearings. The temperature of cylindrical roller bearings increased When running the evaporative cooler more than bush bearings. the noise of Evaporative Cooler by using both types of Bearings was almost same but with a little Reduce by using cylindrical roller Bearings. Which means the Evaporative Cooler has better Performance by using bush bearings than using cylindrical roller bearings.

Designing a Formulation of the Nootropic Drug Aniracetam Using 2-Hydroxypropyl-β-Cyclodextrin Suitable for Parenteral Administration.

The nootropic drug aniracetam is greatly limited in its application by low aqueous solubility and a poor oral bioavailability. The primary aim of this study was to design a parenteral formulation of aniracetam that can be administered intravenously. Complexation of aniracetam with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated as a strategy to enhance solubility. A phase solubility analysis was performed to quantify the extent of improvement. An 819% increase in the solubility of aniracetam was obtained, reaching 36.44 mg/mL. This marked increase enables aniracetam to exist in an aqueous solvent at levels sufficient for parenteral dosing. A stability test was then devised using a design of experiment approach. The aniracetam-HP-β-CD formulation was subjected to different relative humidity and temperature and cyclodextrin concentrations over a 12-week period. Key changes in FTIR vibrational frequencies suggest the benzene moiety of aniracetam was introduced into the hydrophobic cavity of HP-β-CD. These results are highly supportive of the formation of a predictable 1:1 molar stoichiometric inclusion complex, explaining the improvement seen in physiochemical properties of aniracetam following formulation with HP-β-CD. This novel formulation of aniracetam suitable for parenteral administration will have utility in future studies to further elucidate the pharmacokinetics of this drug.

Vibration reduction performance parameters matching for adaptive tunable vibration absorber

Based on the principle of vibration absorber, an adaptive tunable vibration absorber with the magnetorheological elastomer as the core intelligent component was designed to eliminate variable frequency vibration of the powertrain system. The simulation of the magnetic circuit of the adaptive tunable vibration absorber was carried out to ensure the magnetic field generated by the design with a closed magnetic circuit could meet the requirement. The transient dynamic simulation analysis of the adaptive tunable vibration absorber shows that the natural frequency of the vibration absorber could well follow the external excitation signal. The natural vibration sensitivity analysis of the 4-degree-of-freedom dynamic system of the powertrain system was performed to obtain the key moment of inertia that affects the natural frequencies of each stage and then the installation position of the adaptive tunable vibration absorber corresponding to external excitation near the resonant frequency band could be determined. Subsequently, taking the third natural vibration as an example, an adaptive tunable vibration absorber with corresponding variable-stiffness range was installed on the key moment of inertia affecting the vibration of this order. The transient changes of each natural vibration frequency of the powertrain system with the adaptive tunable vibration absorber were studied and then the best starting and stopping frequencies were determined. According to the optimal frequency tuning scheme, the variation range of the storage modulus required for the magnetorheological elastomer material in the limited magnetic field range was obtained. The relationship between the controllable current and the torsional stiffness of the vibration absorber is established. Aiming at the vibration problem near the third-order natural vibration, the best vibration reduction performance parameters were matched to the adaptive tunable vibration absorber. Finally, a time-frequency analysis was applied to the powertrain system with adaptive tunable vibration absorber, and the result shows that the best performance parameter matching for the adaptive tunable vibration absorber could effectively improve its vibration reduction performance.

Computational study of halogen-free Boron based dicationic ionic liquids of [bis-Mim][BMB]2 and [bis-Mim][BScB]2.

In this paper, the structures and energetics of 1,3-bis[3-methylimidazolium-yl] pentane ([bis-Mim]2+) dication and bis(mandelato) borate [BMB]- and bis(salicylato) borate [BScB]-anions in isolated forms, ion pairs (IPs) and dicationic ionic liquids (DILs) were studied by Density Functional Theory (DFT) at the M06-2X/6-31G(d,p) level of theory. According to the IUPAC criteria, the hydrogen bonds between anion and cation were characterized and classified in the optimized geometries of the isolated ions, IPs and DILs. Inspection of the optimized structures revealed that the interionic hydrogen binding has important effect on the ions structures. The interaction energies between a dication and anions have been described in terms of NBO charge distribution, the stabilization energy E(2) values, changes of vibrational frequencies and the reduced density gradient (RDG) analysis. Also, the reactivity and interactions between chemical species were interpreted in terms of global electronic properties. Electrostatic potential surfaces (ESP) have been applied for visualizing the charge related properties and characterization of the most energetic sites of isolated ions and ion complexes.

Energetics and Vibrational Signatures of Nucleobase Argyrophilic Interactions.

This study investigates the interactions of both purine (adenine and guanine) and pyrimidine (cytosine, thymine, and uracil) nucleobases with a pair of silver atoms (Ag2). Full geometry optimizations were performed on several structures of each nucleobase/Ag2 complex and the corresponding isolated monomers using the M06-2X density functional with a correlation consistent triple-ζ basis set augmented with diffuse functions on all atoms and a relativistic pseudopotential on Ag (aug-cc-pVTZ for H, C, N, and O and aug-cc-pVTZ-PP for Ag; denoted aVTZ). Harmonic vibrational frequency computations indicate that each optimized structure corresponds to a minimum on the M06-2X/aVTZ potential energy surface. Relative electronic energies for interactions between Ag2 and each nucleobase were compared to elucidate energetic differences between isomers. Further analysis of the changes in vibrational frequencies, infrared intensities, and Raman scattering activities reveals how different Ag2 binding sites might be differentiated spectroscopically. These results provide molecular-level insight into the interactions between nucleobases and silver, which may lead to better understanding and interpretation of surface-enhanced Raman spectroscopy experiments on nucleobases and related systems.

Monitoring local damage due to fatigue in plate girder bridge

About 95% of all fatigue damage to plate girder bridges occurs at the front of soleplates, the edge of gusset plates, and the upper end of vertical stiffeners. In the present study, the changes in vibration frequency and main-girder deflection that are generally used as indices to monitor the condition of a bridge were analytically investigated to determine their effectiveness, using a model that considered the influence of the types of fatigue cracks present in a real bridge. The results of a natural vibration analysis and a dynamic analysis that considered a vehicle traveling on the bridge showed that the dynamic deflection response and the vibration characteristics of the bridge changed as damage progressed. It was found to be possible to identify the conditions leading up to serious fracture of the main member and total bridge collapse. However, it was more difficult to detect incipient fatigue cracks and fracture of secondary members.

RETRACTED: Detection of eccentricity fault based on vibration in the PMSM

Abstract This paper presents how to diagnose faults in static and dynamic eccentricity of a rotor by observing the vibration of permanent magnet synchronous motor. The radial electromagnetic force density of the permanent magnet synchronous motor is represented as the square of the air-gap flux density based on the Maxwell stress tensor, which is applied to the stator to cause the vibration. The distribution of air-gap flux density changes with the static and dynamic eccentricity so the changes of vibration order and frequency of radial electromagnetic force density will be considered with formulas. In result, the static eccentricity changes the vibration order while the dynamic eccentricity changes both vibration order and frequency. By applying it to the target model, 6-pole and 9-slot permanent magnet synchronous motors, the static eccentricity generates the vibration order of the original frequency, r = 2. In addition, the dynamic eccentricity generates vibration order, r = 2, not at the original frequency, but at the sideband frequency. It means that the static eccentricity increases the vibration of the original frequency and the dynamic eccentricity generates the sideband frequency while the vibration of the original frequency changes relatively little. The last proposal was verified with the finite element analysis and tests.

Vibration-Based Diagnostics of Transverse Surface Cracks in Rods of Different Cross Section Under Longitudinal Vibrations

The paper considers the results of determining the vibrodiagnostic indicators of the presence of various mode I breathing transverse cracks in rod elements of rectangular and circular cross section with different boundary conditions under longitudinal vibrations. Relative second harmonic amplitudes in the vibration spectrum at the main and superharmonic resonance of the first eigenmode of cantilever rods without mass and with a mass at the end and rods with the ends free for longitudinal displacements under forced and kinematic vibration excitation were taken as diagnostic indicators. To determine the above indicators, analytical and numerical bending vibration methods considered before are used. In the analytical solution, the nonlinearity parameter of the vibrating system is calculated using the corresponding values of stress intensity factors. The numerical solution is performed on the basis of eight-node finite element models with the representation of a breathing crack as a mathematical cut and the treatment of a contact problem in the formulation providing mutual nonpenetration between crack faces. Plots of the values of diagnostic indicators as a function of relative crack depth, crack location and the site of measurement of longitudinal displacements have been obtained. Comparisons of values of diagnostic indicators with the value of relative change in natural vibration frequency are presented. It has been shown that at the main resonance, the numerical solution confirms the pronounced effect of localization of diagnostic indicators in the crack region. It has been found that at the superharmonic resonance, the value of the vibrodiagnostic indicator is two orders of magnitude higher than that of the indicators at the main resonance, but the effect of their localization near the crack does not practically manifest itself. Some localization is observed for the absolute values of the second harmonic, and only for longitudinal strain, there is a strongly pronounced effect. A comparison of the obtained values of diagnostic indicators with the data for bending vibrations is given. It is noted that in spite of basically lower indicators under longitudinal vibrations, they have an advantage in terms of the possibility to diagnose symmetric both surface and internal breathing cracks.

Determination of the Vibration Diagnostic Parameters Indicating the Presence of a Mode I Crack in a Blade Airfoil at the Main, Super- and Subharmonic Resonances

The paper presents the results of numerical calculations to determine the regularities underlying the influence of the characteristics of a mode I breathing fatigue crack on the leading edge of the aircraft gas turbine engine blade airfoil – that is responsible for the nonlinearity of the vibratory system – on its flexural forced vibration behavior. Their comparison with similar data for the rod of a rectangular cross section has shown satisfactory agreement. The calculation of the vibration diagnostic parameters indicating the presence of damage is performed using the developed finite element models of the investigation objects whose forced vibrations were excited by the kinematic displacement of fixed edge elements. The breathing crack is modeled as a mathematical cross section, the non-penetration of its faces is ensured by solving the contact problem of their interaction. The problem of the system forced vibrations is solved using the Newmark method and fast Fourier transformation. The obtained amplitude-frequency characteristics of the undamaged and damaged blade airfoil are indicative of the increase in the energy dissipation in the system in the presence of a breathing crack. The change in the resonant vibration frequency of the cracked object of investigation and the amplitude ratio of the dominant harmonics of displacements and accelerations (the ratio of the former to the latter at the superharmonic resonance and the latter to the former at the main and subharmonic resonances) were chosen as the vibration diagnostic indicators of damage. The amplitude ratio of the dominant harmonics of accelerations at the superharmonic resonance and that of displacements at the subharmonic resonance is found to be the most sensitive indicator of the presence of cracks.

Investigation of NiTi based damper effects in bridge cables vibration response: Damping capacity and stiffness changes

Due to aerodynamic instabilities induced by combination of rain and wind, civil engineering cables are submitted to cyclic loadings during their whole operating life. To prevent them from fatigue issues, internal and external dampers are increasingly used.Recently, innovative damping devices based on Shape Memory Alloys have demonstrated a true efficiency, thanks to their dissipation properties. Indeed, near-equiatomic Nickel-Titanium alloys (NiTi) present an interesting damping capacity due to a solid-solid displacive phase transformation of austenite into martensite. This transformation occurs under thermal and/or mechanical loadings.Two different damping devices embedding NiTi wires are presented in this paper. Both are evaluated ad hoc, using a full-scale vibration cable bench under several loading and environment configurations. The effectiveness of the damping device has been demonstrated. A direct link has been made between the system “cable + damper” vibration response and NiTi behaviour. First, results show that several damping regimes observed during mitigation of the cable vibration amplitude are due to NiTi microstructural changes and phase transformations. Secondly, this paper demonstrates that stiffness and vibration frequency changes are governed by the NiTi stress-strain curve secant stiffness modulus.