Damping Measurements Research Articles

Enhancement in corrosion resistance and vibration damping performance in titanium by titanium nitride coating

Titanium nitride (TiN) thin films are deposited on titanium (Ti) substrates by pulsed laser deposition and radio frequency magnetron sputtering. The main goal of this research is to improve the corrosion resistance and the vibration damping performance of the Ti substrates by surface modification of the substrates with TiN thin film coatings. Electrochemical results indicate that TiN films bring about a significant improvement in the corrosion resistance of the Ti disks in phosphate buffer saline solution. It is also observed that TiN deposited at room temperature has the best corrosion efficiency in terms of lower corrosion current density and more positive corrosion potential. From the damping measurements, it is observed that the damping ratios of the TiN-coated beams are one to two orders of magnitude greater than those of uncoated ones. Additionally, the damping amplitudes of the TiN coated beams have been observed to return to zero position faster than the uncoated beam. The energy dissipation due to internal friction at the beam-coating interface and inter-lamellae interface within TiN coatings can be the mechanism responsible for reducing vibration amplitudes of TiN-coated beams.

Improving the damping behavior of fiber-reinforced polymer composites with embedded superelastic shape memory alloys (SMA)

One-way shape memory alloy wires exhibiting super elastic properties are capable of generating high recovery stresses under constrained conditions upon external mechanical loading. In the present work, the damping response of hybrid composite materials enhanced with super-elastic NiTi alloy wires is examined. The studied system consisted of an aramid reinforced epoxy resin composite in which NiTi wires have been embedded. By conducting damping measurements it was found that the addition of Ni–Ti wires into the aramid/epoxy composite leads to a significant modification of its damping which depends strongly on wire volume fraction. This paves the way for the design of a new class of hybrid materials that combine the stiffness and strength of reinforcing fibers with the increased damping tuning capability offered by the NiTi wires.

A Bayesian model updating with incomplete complex modal data

Abstract Finite element (FE) model updating using measured dynamic data has gained much attention in view of its contribution towards important areas like model-correction, structural health monitoring. Usually model updating is observed to be performed using measured modal data like modal frequencies and mode shapes – indeed very few works are observed to provide scope for using damping measurements in FE model updating. The present work proposes a Bayesian probabilistic FE model updating using multiple sets of complex modal data (viz. complex modal frequencies and complex mode shapes) and thereby enabling the scope for incorporating damping measurements in updating. Moreover there remains the opportunity for using incomplete complex modal data and avoiding the requirement of mode matching. In this paper, a computationally efficient model updating approach based on maximum a posteriori (MAP) is formulated where all the mass, stiffness and damping parameters are updated in a sequential iterative manner. Detailed formulations are obtained considering damping to be contributed by classical damping (Rayleigh damping) and non-classical viscous damping. Besides, formulations for uncertainty estimation and probabilistic damage detection are also developed. The proposed approach is validated using two numerical examples while utilizing incomplete complex modal data. Performance in updating is evaluated for both undamaged and damaged cases. The proposed approach is observed to be successful for updating of FE model as well as for detection of changes/damages in probabilistic manner, while being computationally efficient as well.

HOM damping requirements and measurements for CEPC 650-MHz 2-cell cavity

The circular electron–positron collider (CEPC) will use a 650-MHz RF system with 240 two-cell cavities for the collider. The collider is a double ring with shared cavities for Higgs operation and separate cavities for W and Z operations. The higher-order modes (HOM) excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. To get the real damping results, two prototypes of HOM coupler have been fabricated and installed on the 650-MHz two-cell cavity. The HOMs have been verified by bead pulling method. A test bench with two 2-cell cavities is used to measure the real damping results and study HOM propagating properties for a cavity string. In this paper, the impedance budget, HOM damping and HOM power requirements for the CEPC collider ring are given. The damping results measured for the fundamental mode and HOMs seem good compared with the simulated results. The absorbing efficiency of the absorber and the extraction power efficiency of HOM couplers were also achieved.

Comment on "Slow passage through resonance".

In a recent numerical and analytical study, Park etal. [Phys. Rev. E 84, 056604 (2011)PLEEE81539-375510.1103/PhysRevE.84.056604] presented the statement that a linearly damped harmonic oscillator subject to a linear frequency chirp ω_{f}(t)=ω_{0}+εt experiences "an early onset of resonance, setting in when the ramped forcing frequency is midway between its initial value ω_{0} and the natural frequency ω_{n} for resonance in the unforced problem," i.e., the resonance occurs when the instantaneous frequency ω_{inst} approaches (ω_{0}+ω_{n})/2. This statement is not valid because the instantaneous frequency of the forcing function actually grows twice as fast as stated in the paper, and the resonance actually occurs for instantaneous forcing frequency ω_{inst} approximately equal to the natural frequency ω_{n}. We also highlight the difference between the critical frequency ramp rate for resonance amplitude measurement and the critical frequency ramp rate for resonance frequency and damping measurements.

Damping of surface waves due to crude oil/oil emulsion films on water

In this paper results of laboratory studies of damping of gravity-capillary waves due to emulsified oil films (EOF) are presented and compared to crude oil films (COF). A laboratory method based on measuring the damping coefficient and the length of parametrically generated gravity-capillary waves is applied to a 50% EOF and to crude oil films. Measurements of wave damping were carried out in a range of surface wave lengths, corresponding to Bragg waves of X- to Ka-band radars. The obtained dependences of wave damping coefficient on EOF thickness have demonstrated the existence of a damping maximum at thicknesses of about 1–2 mm, and the maximum is approximately twice the one for COF, the damping maximum for EOF is located at larger film thicknesses than for COF. Theoretical calculations of wave damping have been performed and viscoelastic parameters of EOF have been estimated from comparison between theory and experiment.

Responsivity and sensitivity of piezoelectric MEMS resonators at higher order modes in liquids

Micromachined resonators completely submerged in liquids suffer from high viscous damping and low measurement signals compared to the operation in gaseous environment or in vacuum, which drastically decreases the sensing performance. A promising approach to decrease damping is the utilization of higher order modes. However, with the increase in mode order also the fluid-structure interaction decreases. In this context, it is unclear how the use of higher order modes helps, when targeting the characterization of fluid properties such as density and viscosity. In this paper, we demonstrate how the use of higher order modes affects both the responsivity and sensitivity of resonantly excited MEMS sensors when operated in liquids. The latter two key device parameters are experimentally investigated with respect to the inverse viscosity-density product (ρfluid·μfluid)-0.5 for the quality factor Q, the electrical conductance peak height ΔG and for the resonance frequency fres in standardized liquids with dynamic viscosity values ranging from 5 to 700 mPa∙s. It is observed, that an increase in mode order significantly increases the quality factor by a factor of 7, when comparing 1st to 10th order mode in a sample fluid with a dynamic viscosity of 5 mPa∙s), allowing the characterization of high viscous liquid with a dynamic viscosity up to 700 mPa∙s. Even so, no influence on the relative responsivity of Q and ΔG is observed. In fact, a decrease in the relative responsivity of fres is observed, so that no gain in response is achieved for all three parameters when the mode order is increased. However, higher order modes show significantly improved strain profiles on the surface of the resonating structure, resulting in increased ΔG values for the piezoelectric readout mechanism. Therefore, the sensitivity is substantially increased resulting in an improvement by a factor of ˜30, when comparing the 1st and 10th order mode. Even higher factors of ˜50 are obtained for Q and ΔG, what enables a minimal detectable (ρ·μ)−0.5 value of 0.000998 (mPa·s·kg/l)−0.5in a high viscous sample fluid with (ρ·μ)−0.5 = 0.040 (mPa·s·kg/l)−0.5 (for comparison: a common engine oil such as SAE 5W-40 has (ρ·μ)−0.5 = 0.039 (mPa·s·kg/l)−0.5at 0 °C).

Experimental design for the accurate measurement of ultra-low damping of simple structures

As a means of validating numerical models, recent research has shown a need for methodology to measure the structural damping of very lightly damped structures (loss factor < 0.005) to a high level of accuracy. Traditional experimental methods of measuring structural damping must be altered to accurately capture the lightly damped response. Otherwise, inaccurate damping values will be calculated that are larger than those intrinsically found in the material/structure. This presentation focuses on experimental technique modifications required for frequency domain methods of measurement of ultra-low damped structures. First, the implications of less accurate capture of resonant peaks in frequency response functions will be explored. Typical short frame, uniform frequency spacing can result in large measurement errors with lightly damped test articles. Instead, long time histories, focused sine-based testing, zero-padding, and peak approximation methods should be utilized for improved accuracy. Additionally, the effects of isolation-related boundary conditions and instrumentation mass to measurement accuracy are explored and quantified. As a means of validating numerical models, recent research has shown a need for methodology to measure the structural damping of very lightly damped structures (loss factor < 0.005) to a high level of accuracy. Traditional experimental methods of measuring structural damping must be altered to accurately capture the lightly damped response. Otherwise, inaccurate damping values will be calculated that are larger than those intrinsically found in the material/structure. This presentation focuses on experimental technique modifications required for frequency domain methods of measurement of ultra-low damped structures. First, the implications of less accurate capture of resonant peaks in frequency response functions will be explored. Typical short frame, uniform frequency spacing can result in large measurement errors with lightly damped test articles. Instead, long time histories, focused sine-based testing, zero-padding, and peak approximation methods should be utilized for improved accuracy. Additionally...

Efficacy of high-performance ceiling systems

A current approach to try to solve a low frequency impact-induced structure-borne noise issue in lightweight woodframe buildings has been the application of a resilient ceiling suspended by one-inch deflection spring hangers. While this system has been lab tested it was only compared to an assembly with no isolation in which the gypsum board was directly attached to the bottom of the joists. The authors have repeated the testing of one-inch deflection ceiling hangers in the same lab but this time they compared it to the same isolators with the springs removed, standard resilient sound clips and other ceiling isolation systems. Relative performance differences of the isolation systems will be presented along with transmissibility, static stiffness, dynamic stiffness and damping measurements of each isolation element. A few theories as to why the systems behave the way they do will also be presented.

Effect of natural fibre reinforcement on the sound and vibration damping properties of bio-composites compression moulded by nonwoven mats

Abstract Biodegradable natural fibre composites are increasingly developed for lightweight structural applications in automobile and construction industries with significant environmental benefit. This work aims to explore the sound and vibration properties of natural fibre composites that inevitably suffer menace of vibrations during their operations as engineering structures. Natural fibres (bamboo, cotton, flax) and polylactic acid (PLA) fibres were blended, carded, laid up and finally needle-punched to nonwoven mats before being consolidated at elevated temperature under compression. Vibration damping and acoustic measurements were conducted on these natural fibre composites and their behaviour was compared to that of a commercial panel, made of polypropylene (PP) matrix reinforced with hemp and kenaf fibres. From both the coincidence frequency analysis and wave number amplitude analysis, the cotton/bamboo/PLA composite laminate showed the best acoustic performance (coincidence frequency of 2448 Hz) that is related to the fineness of cotton fibres, bending stiffness, natural frequency and density of the composite panel. The results suggest that the bamboo/cotton hybrid composites can be a viable candidate for engineering applications that require good bending properties, high sound absorption and vibration damping properties.

Evaluation of Rayleigh Damping Coefficients for Laminated Rubber Bearing Components Using Finite Element and Experimental Modal Analysis

Laminated rubber bearing is a significant device found in structures such as bridges and buildings. It is used to isolate the foundation and the superstructure from seismic loads. Since it is made up from a combination of rubbers and steel plates in alternate layers which make the laminated rubber bearing a complex material, the measurements of damping of the laminated rubber bearing is difficult in practice. Damping is a dissipation of energy or energy losses in the vibration of the structure when the structures are excited with external dynamic loading. An accurate value of damping is very important as damping plays a crucial role in fixing the borderline between stability and instability in many structural systems. Therefore, it is essential to determine the accurate value of damping in structural analysis. Finite element and experimental modal analysis is one of the methods that can be used to determine dynamic properties including damping in any structures. Hence, the main objectives of this research are to determine the natural frequencies, mode shapes, Rayleigh’s damping coefficients, α and β and to evaluate the performance of the laminated rubber bearing components i.e. steel and rubber plates using finite element and experimental modal analysis. Based on the finding, the finite element modal analysis with the added Rayleigh’s damping coefficients α and β shows a good agreement with the experimental modal analysis in term of natural frequencies and mode shapes. The value of natural frequencies reduces after the Rayleigh’s damping coefficients are added into the finite element modal analysis and the minimum and maximum displacement are found to be unaffected by the Rayleigh’s damping coefficients for rubber plate. It can be concluded that modal analysis method can be used to estimate the accurate values of damping ratio and to determine the Rayleigh’s damping coefficients α and β as well.

Magnetoelastic excitation of single nanomagnets for optical measurement of intrinsic Gilbert damping

We report an alternative all-optical technique to drive and probe the spin dynamics of single nanomagnets. Optically generated surface acoustic waves (SAWs) drive the magnetization precession in nanomagnets via magnetoelastic (MEL) coupling. We investigate the field-swept dynamics of isolated Ni nanomagnets at various SAW frequencies and show that this method can be used to accurately determine the intrinsic Gilbert damping of nanostructured magnetic materials. This technique opens a new avenue for studying the spin dynamics of nanoscale devices using nonthermal (``cold'') excitation, enabling direct observation of the MEL driven dynamics.

Temperature dependent measurement of internal damping of austenitic stainless steels

This article is aimed on the analysis of the internal damping changes of austenitic stainless steels AISI 304, AISI 316L and AISI 316Ti depending from temperature. In experimental measurements only resonance method was used which is based on continuous excitation of oscillations of the specimens and the whole apparatus vibrates at the frequency near to the resonance. Microplastic processes and dissipation of energy within the metals are evaluated and investigated by internal damping measurements. Damping capacity of materials is closely tied to the presence of defects including second phase particles and voids. By measuring the energy dissipation in the material, we can determine the elastic characteristics, Youngs modulus, the level of stress relaxation and many other.

Re-entrant spin glass transitions: new insights from acoustic absorption by domain walls

Re-entrant spin glass (RSG) transitions in Ni-Mn and Au-Fe have been reassessed by acoustic measurements of the magneto-mechanical damping by domain walls. Stress-induced non-thermally activated domain wall dynamics is progressively replaced by an intense thermally activated relaxational response when the temperature approaches the RSG freezing point. A “frozen” state with negligible motion of domain walls on atomic and mesoscopic scales occurs in the RSG. We propose that RSG freezing has its origin in intrinsic properties of domain walls.

Dynamic Characterization of an Integral Squeeze Film Bearing Support Damper for a Supercritical Co2 Expander

The present work advances experimental results and analytical predictions on the dynamic performance of an integral squeeze film damper (ISFD) for application in a high-speed super-critical CO2 (sCO2) expander. The test campaign focused on conducting controlled orbital motion mechanical impedance testing aimed at extracting stiffness and damping coefficients for varying end seal clearances, excitation frequencies, and vibration amplitudes. In addition to the measurement of stiffness and damping, the testing revealed the onset of cavitation for the ISFD. Results show damping behavior that is constant with vibratory velocity for each end seal clearance case until the onset of cavitation/air ingestion, while the direct stiffness measurement was shown to be linear. Measurable added inertia coefficients were also identified. The predictive model uses an isothermal finite element method to solve for dynamic pressures for an incompressible fluid using a modified Reynolds equation accounting for fluid inertia effects. The predictions revealed good correlation for experimentally measured direct damping, but resulted in grossly overpredicted inertia coefficients when compared to experiments.

UNDERSTANDING THE PHYSICS OF KAPPA (Κ0): INSIGHTS FROM THE EUROSEISTEST NETWORK

this study we estimate the spectral decay factor κ0 for the EUROSEISTEST array. Site conditions range from soft sediments to hard rock over 14 surface and 6 downhole accelerographs. First, we separate local and regional high frequency attenuation and measure κ0. Second, we use the existing knowledge of the geological profile and material properties to correlate κ0 with different site characterisation parameters (Vs30, resonant frequency, depth-to-bedrock). Third, we use our results to improve our physical understanding of κ0. We propose a conceptual model comprising two new notions. On the one hand, we observe that κ0 stabilises for high Vs values; this may indicate the existence of regional values for hard rock κ0. If so, we propose that borehole measurements may be useful in determining them. On the other hand, we find that material damping may not suffice to account for the total measured attenuation. We propose that, apart from damping, additional site attenuation may be caused by scattering from small-scale profile variability. If this is so, then geotechnical damping measurements may not suffice to infer overall crustal attenuation under a site; but starting with a regional (borehole) value and adding damping, we might define a lower bound for site-specific κ0.

Experimental and frequency-domain study of acoustic damping of single-layer perforated plates

Perforated plates/liners have been widely applied in aeroengines and gas turbines to dissipate unwanted noise. In this work, numerical simulations and experimental study of acoustic damping performance of single-layer perforated plates are conducted. For this, a frequency-domain numerical model is developed via solving 3-dimensional Helmholtz equations. The model validation is performed first by evaluating and comparing the calculated acoustic damping performances of three perforated plates with the experimental results available in literature. These plates are perforated with a number of circle-shaped orifices, which have different porosities σ. Each plate backed by a resonant cavity is placed at the end of a rectangular-shaped pipe with a loudspeaker implemented on the other end. To simulate real engines, a mean flow (also known as bias flow) is applied to pass through the perforated orifices. The effects of 1) the mean flow Mach number Ma, 2) the resonance parameter Q, 3) the porosity σ and 4) the plate thickness T are studied one at a time. Acoustic damping performance of these plates is characterized by using sound absorption coefficient α and specific acoustic impedance z. It is found that sound absorption coefficient α is increased first and then decreased with increased Ma. The real part of z characterizing acoustic resistance/damping is linearly increased, as Ma is increased. However, the imaginary part of z characterizing acoustic reactance remains almost unchanged. It is also found that the presence of the bias flow greatly increases the maximum sound absorption coefficient αmax by approximately 33% in comparison with that of without mean flow. The plate thickness T is shown to shift the frequency corresponding to the maximum sound absorption coefficient. Comparing the present simulation results with the experimental and analytical ones available in the literature reveals that good agreement is obtained at lower frequency range. However, as frequency is increased, the model predicts that the bias flow leads to the local αmax reduced by 15%. The plate with a larger thickness is associated with another local αmax, which is not observed for a lower thickness plate. Finally, experimental measurements of the acoustic damping of 2 single-layer in-duct perforated plates are performed. The frequency-domain model is then applied to simulate the experiment. Good agreement between our experimental and numerical results is obtained.

Effect of carbon on the damping capacity and mechanical properties of thermally trained Fe-Mn based high damping alloys

The effect of C on the damping and mechanical properties of thermally trained Fe-17wt%Mn-X wt%C (0<X<0.06) high-damping alloys was analyzed by the impulse internal friction technique and uniaxial tensile tests. The alloys were subjected to a combination of thermo-mechanical processing and thermal cycling which resulted in a C content independent phase fraction and grain size of ɛ-martensite and γ-austenite. The ɛ↔γ phase transformation and the anti-ferromagnetic transition in the γ-phase were observed in the temperature-dependent damping and modulus measurements, respectively. While C had no influence on the intrinsic internal friction of the γ-phase, small amounts of C significantly reduced the damping associated with the motion of ɛ-γ interface boundaries and the widening of stacking faults by the movement of partial dislocations. The C content at which these relaxation processes were suppressed, i.e. approximately 0.03wt%C, coincided with the onset of dynamic strain aging as inferred from the appearance of serrations on the flow curves.

Seismic damage diagnosis of a masonry building using short-term damping measurements

It is of considerable importance to perform dynamic identification and detect damage in existing structures. This paper describes a new and practical method for damage diagnosis of masonry buildings requiring minimum computational effort. The method is based on the relative variation of modal damping and validated against experimental data from a full scale two storey shake table test. The experiment involves a building subjected to uniaxial vibrations of progressively increasing intensity at the facilities of EUCENTRE laboratory (Pavia, Italy) up to a near collapse damage state. Five time-histories are applied scaling the Montenegro (1979) accelerogram. These strong motion tests are preceded by random vibration tests (RVT's) which are used to perform modal analysis. Two deterministic methods are applied: the single degree of freedom (SDOF) assumption together with the peak-picking method in the discrete frequency domain and the Eigen realisation algorithm with data correlations (ERA-DC) in the discrete time domain. Regarding the former procedure, some improvements are incorporated to locate rigorously the natural frequencies and estimate the modal damping. The progressive evolution of the modal damping is used as a key indicator to characterise damage on the building. Modal damping is connected to the structural mass and stiffness. A square integrated but only with two components expression for proportional (classical) damping is proposed to fit better with the experimental measurements of modal damping ratios. Using this Rayleigh order formulation the contribution of each of the damping components is evaluated. The stiffness component coefficient is proposed as an effective index to detect damage and quantify its intensity.

Measurements of wave damping by a grease ice slick in Svalbard using off-the-shelf sensors and open-source electronics

ABSTRACTVersatile instruments assembled from off-the-shelf sensors and open-source electronics are used to record wave propagation and damping measured by Inertial Motion Units (IMUs) in a grease ice slick near the shore in Adventfjorden, Svalbard. Viscous attenuation of waves due to the grease ice slick is clearly visible by comparing the IMU data recorded by the different instruments. The frequency dependent spatial damping of the waves is computed by comparing the power spectral density obtained from the different IMUs. We model wave attenuation using the one-layer model of Weber from 1987. The best-fit value for the effective viscosity is ν = (0.95 ± 0.05 × 10−2)m2 s−1, and the coefficient of determination is R2 = 0.89. The mean absolute error and RMSE of the damping coefficient are 0.037 and 0.044m−1, respectively. These results provide continued support for improving instrument design for recording wave propagation in ice-covered regions, which is necessary to this area of research as many authors have underlined the need for more field data.