Bending Resonance Research Articles

A Novel Structure to Suppress Transverse Modes in Radio Frequency TC-SAW Resonators and Filters

In this letter, we present simulation and measurement results of a novel structure to suppress transverse modes in radio frequency temperature-compensated surface acoustic wave (TC-SAW) resonators and filters. We propose a bent TC-SAW resonator structure to suppress such transverse modes which in general trapped between the busbars, based on the fact that higher TC-SAW wave modes in the resonator suffer higher loss at the resonator boundary. The higher wave modes leak energy out from the resonator busbars after multiple bounces along the length of the resonator. By adding this structure to our existing transverse mode suppression technique, we successfully suppress the bulk of the transverse modes in the resonators and filters. To test the effectiveness of the proposed structure, we fabricate the bent resonators and filters in a standard TC-SAW fabrication process on 128YX lithium niobate (128YX-LN) substrate. The measured long-term evolution band 39 filter response shows the effectiveness of this structure in suppressing transverse modes.

Willis Metamaterial on a Structured Beam

Bianisotropy is common in electromagnetics whenever a cross-coupling between electric and magnetic responses exists. However, the analogous concept for elastic waves in solids, termed as Willis coupling, is more challenging to observe. It requires coupling between stress and velocity or momentum and strain fields, which is difficult to induce in non-negligible levels, even when using metamaterial structures. Here, we report the experimental realization of a Willis metamaterial for flexural waves. Based on a cantilever bending resonance, we demonstrate asymmetric reflection amplitudes and phases due to Willis coupling. We also show that, by introducing loss in the metamaterial, the asymmetric amplitudes can be controlled and can be used to approach an exceptional point of the non-Hermitian system, at which unidirectional zero reflection occurs. The present work extends conventional propagation theory in plates and beams to include Willis coupling, and provides new avenues to tailor flexural waves using artificial structures.

Fatigue Testing of Large-Scale Steel Structures in Resonance with Directional Loading Control

Offshore structures such as jacket and monopile foundations for wind towers and platforms for oil and gas are large steel structures that are subjected to severe fatigue loading conditions. When developing constructions using novel welding techniques, high-strength steel grades or specific bolted assemblies there is a need for validation testing of large-scale components. Conventionally, such fatigue tests are carried out on servo-hydraulic test which are time-consuming.Alternatively, fatigue tests can be performed in resonant bending by a cyclic excitation force with frequency close to the first eigenfrequency of the test specimen. In this paper a new test setup is presented suitable for testing large-scale steel components in resonance with control of the loading direction by two counter-rotating excentric masses.A wide range of loading conditions can be applied with a frequency from 20 to 40 Hz. The test specimen, that can weigh up to 25 ton, is supported in the nodes of its natural wave-form, so that no dynamic forces are transmitted to the setup.The working principles of the test setup are illustrated based on test results of a 711 mm diameter x 25.4 mm wall thickness steel pipe, a welded X-node representative for a welding detail of an offshore jacket foundation structure and a large-scale HE-beam. Crack initiation is detected using acoustic emission while crack growth is monitored by local strain gauge measurements as well as the global stiffness reduction of the test specimen. Finally, the beach marking method is used to visualize crack fronts for post-mortem analysis.

Strength, elasticity and the limits of energy dissipation in two related sea urchin spines with biomimetic potential

The calcitic spines of the sea urchins Heterocentrotus mamillatus and H. trigonarius are promising role models for lightweight applications, bone tissue scaffolds and energy dissipating processes due to their highly porous and organized structure. Therefore, mechanical properties including Young’s Modulus, strength, failure behaviour and energy dissipation efficiency have been investigated in depth with uniaxial compression experiments, 3-point bending tests and resonance frequency damping analysis. It was found that despite a very similar structure, H. trigonarius has a significantly lower porosity than H. mamillatus leading to a higher strength and Young’s Moduli, but limited ability to dissipate energy. In order to show reliable energy dissipation during failure in uniaxial compression, a transition porosity of 0.55–0.6 needs to be exceeded. The most effective structure for this purpose is a homogeneous, foam-like structure confined by a thin and dense shell that increases initial strength and was found in numerous spines of H. mamillatus. Sharp porosity changes induced by dense growth layers or prominent wedges of the spines’ radiating building principle act as structural weaknesses, along which large flakes can be spalled, reducing the energy dissipation efficiency considerably.The high strength and Young’s Modulus at the biologically necessary high porosity levels of the spines is useful for Heterocentrotus and their construction therefore remains to be a good example of biomimetics. However, the energy dissipative failure behaviour may be regarded as a mere side effect of the structure.

Young’s modulus and fatigue investigation of aluminum nitride films deposited on 304 stainless steel foils using micro-fabricated cantilevers

Aluminum nitride based (AlN-based) piezoelectric vibration energy harvesters (PVEHs) have been received much attention in the power generation for the device in microelectromechanical systems (MEMS). During the long-time vibration, PVEHs are suffering cyclically dynamic stress. This may result in the defect of the materials, and finally cause the failure of the device. To achieve a reliable design of the device that can work for a long time without failure, the investigation on the mechanical properties of Young’s modulus and fatigue were conducted for AlN films deposited on 304 stainless steel (SUS 304) foils in this study. Two kinds of materials were tested, SUS 304 foils with a thickness of 50 μm (SUS 304 (50 μm)) and a composite material of AlN films deposited on both sides of SUS 304 foils (AlN (1 μm)/ SUS 304 (50 μm)/ AlN (1 μm) structure). The samples were micro-fabricated to cantilevers. Young’s modulus was measured by the micro-cantilever resonance method. The resonant bending fatigue testing method was used to investigate the fatigue properties of the materials. The displacement amplitude of the samples was recorded during the tests. A new criterion by using the change of amplitude versus number of cycles was proposed to define the fatigue life. As results, the Young’s modulus was 184.9 and 342.9 MPa, for SUS 304 foil and AlN film, respectively. Stress-cycle (S-N) curves were plotted by using the proposed criterion successfully. The fatigue strength of SUS 304 foils and the material with AlN/ SUS 304/ AlN structure was estimated to be 294 and 327 MPa, respectively. Fatigue failures of stable crack, intrusions and extrusions, and slip bands, appeared on the surface of SUS 304 foils after the long time vibration. No fatigue failure or surface defect was observed on AlN films.

A novel planar piezoelectric actuator with nano-positioning ability operating in bending-bending hybrid modes

A planar piezoelectric actuator using bending-bending hybrid modes is proposed. The actuator is composed four uniform transducers that can bend in the horizontal and vertical directions dependently. The actuator can operate in two modes: dynamic mode and quasi-static mode. The dynamic mode uses the hybrid bending resonance modes to achieve a large travelling range with high speed; the quasi-static mode uses the quasi-static horizontal bending to achieve a micrometre travelling range with nanometer resolution. The operating principle is discussed and simulated by finite element method (FEM). Maximum linear and rotary speeds of 19.8 mm/s and 0.266 rad/s are obtained under a voltage of 400 Vp-p and frequency of 11.86 kHz in the dynamic mode. When operating in quasi-static mode, there is a linear relationship between the output displacement and voltage, linear and rotary displacement resolutions of 16 nm and 0.198 μrad are obtained. The actuator can accomplish large travelling range with nano-positioning ability.

Optical absorption spectra of perovskite thin films for defect estimation by photothermal bending spectroscopy

The measurement of the optical absorption coefficient spectra of perovskite thin films of CH3NH3PbI3 by resonant photothermal bending spectroscopy (resonant-PBS) and Fourier-transform photocurrent spectroscopy (FTPS) for the defect estimation of the material has been attempted. A fundamental absorption edge was observed in the photon energy ħω region of 1.5–1.6 eV by both techniques. In addition, extra absorption of about 102 cm−1 was detected at ħω < 1.5 eV only in the spectra measured by resonant-PBS. This extra absorption seems to indicate the existence of localized states in the bandgap of CH3NH3PbI3 films. The difference between resonant-PBS and FTPS profiles below the absorption edge is caused by the difference in measurement mechanism, that is, resonant-PBS utilizes a temperature rise of the sample by the nonradiative recombination of photoexcited carriers, while FTPS measures photocurrent arriving at electrodes by the electric field after the photoexcitation. These results seem to indicate that resonant-PBS is a useful tool for the defect estimation of CH3NH3PbI3.

Damage monitoring of three-point bending concrete specimens by acoustic emission and resonant frequency analysis

The crack propagation process in pre-notched concrete beam specimens, tested in the lab under three-point bending, was monitored by the Acoustic Emission (AE) technique and the extraction of resonant frequencies. The loading process was carried out in displacement-controlled conditions up to the final failure of the specimen. Average frequency vs. RA value analysis was used to characterize the crack propagation mode, whereas the cumulative AE energy and the variation in the resonant bending frequencies were selected as the main parameters to monitor the damage progress due to crack advancement. Moreover, finite element models were implemented to reproduce the load–deflection curve and to evaluate the resonant frequencies for different notch depths. An inverse procedure was therefore applied to estimate the crack advancement based on the measured and calculated frequencies.

Magnetoelectric metglas/bidomain y + 140°-cut lithium niobate composite for sensing fT magnetic fields

We investigated the magnetoelectric properties of a new laminate composite material based on y + 140°-cut congruent lithium niobate piezoelectric plates with an antiparallel polarized “head-to-head” bidomain structure and metglas used as a magnetostrictive layer. A series of bidomain lithium niobate crystals were prepared by annealing under conditions of Li2O outdiffusion from LiNbO3 with a resultant growth of an inversion domain. The measured quasi-static magnetoelectric coupling coefficient achieved |αE31| = 1.9 V·(cm Oe)−1. At a bending resonance frequency of 6862 Hz, we found a giant |αE31| value up to 1704 V·(cm Oe)−1. Furthermore, the equivalent magnetic noise spectral density of the investigated composite material was only 92 fT/Hz1/2, a record value for such a low operation frequency. The magnetic-field detection limit of the laminated composite was found to be as low as 200 fT in direct measurements without any additional shielding from external noises.

Vibrometry Assessment of the External Thermal Composite Insulation Systems Influence on the Façade Airborne Sound Insulation

This paper verifies the impact of the use of an external thermal composite system (ETICS) on air-borne sound insulation. For optimum accuracy over a wide frequency range, classical microphone based transmission measurements are combined with accelerometer based vibrometry measurements. Consistency is found between structural resonance frequencies and bending wave velocity dispersion curves determined by vibrometry on the one hand and spectral features of the sound reduction index, the ETICS mass-spring-mass resonance induced dip in the acoustic insulation spectrum, and the coincidence induced dip on the other hand. Scanning vibrometry proves to be an effective tool for structural assessment in the design phase of ETICS systems. The measured spectra are obtained with high resolution in wide frequency range, and yield sound insulation values are not affected by the room acoustic features of the laboratory transmission rooms. The complementarity between the microphone and accelerometer based results allows assessing the effect of ETICS on the sound insulation spectrum in an extended frequency range from 20 Hz to 10 kHz. The modified engineering ΔR prediction model for frequency range up to coincidence frequency of external plaster layer is recommended. Values for the sound reduction index obtained by a modified prediction method are consistent with the measured data.

Development of a resonant fatigue testing facility for large-scale beams in bending

In this article the development of a resonant bending fatigue test stand for large-scale structural elements at the Institute of Concrete Construction of Leibniz Universität Hannover, Germany, is presented. The aim of the project was to create a controllable forced vibration close to the natural frequency of the tested bending specimens in order to induce fatigue failure in the specimen. By developing a new testing facility and a flexible control system this objective was achieved and initial results of resonant fatigue tests on train rail specimens are presented in this paper. Besides the advantage of the resonant testing system using higher loading frequencies and hence reducing the test duration compared to traditional test stands, the reduction in energy costs is enormous.

Crack growth rates and microstructure feature of initiation region for very‐high‐cycle fatigue of a high‐strength steel

AbstractThe S‐N data up to very‐high‐cycle fatigue (VHCF) regime for a high‐strength steel were obtained by fatigue tests under constant amplitude and variable amplitude (VA) via rotating bending and electromagnetic resonance cycling. Crack initiation for VHCF was from the interior of specimens, and the initiation region was carefully examined by scanning electron microscopy and transmission electron microscopy. Crack growth traces in the initiation region of fine‐granular‐area (FGA) were the first time captured for the specimens under VA cycling by rotating bending. The obtained crack growth rates in FGA were upwards to connect well with those in fish‐eye region available in the literature and were associated well with the calculated equivalent crack growth rates in FGA. The observations of profile samples revealed that FGA is a nanograin layer for the specimens under VA cycling, which is a new evidence to support the previously proposed “numerous cyclic pressing” model.

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

To tackle the lack of efficiency of passive sound absorbing treatments in the low frequency range, a specific arrangement of a poroelastic material is proposed. Compared with the usual uniform layout, giving a lamella network structure to a material provides additional sound absorption below the quarter wavelength resonance frequency at oblique incidence. This is demonstrated experimentally on a sample made of melamine foam lamellas. A numerical approach that incorporates geometric periodicity highlights the mechanisms involved in this additional dissipation, achieved by combining structural and viscous dissi-pation within the lamellas. The shear and bending resonances of the lamellas can be excited at oblique incidence. The frequency of the shear resonance is related to the thickness of the sample, whereas the bending resonance is also a function of the width of the lamellas. These simple dimensional parameters allow adjustable tuning of the associated frequencies at which additional sound absorption can be obtained.

Analysis of fatigue damage of aluminium alloy under multiaxial random vibration

Many studies have investigated the fatigue damage of materials under vibration. However, the mechanism of vibration-induced fatigue damage remains unclear, and no method has been established for evaluating the vibration fatigue strength. Therefore, it is important to establish an evaluation method for the vibration fatigue strength of materials to ensure appropriate strength in their design. In this study, we performed experiments to investigate the fracture mechanism of a material under multi-axial random vibration. We selected aluminium alloy A5056 as the test material and employed button-head-type specimens with a notch. The multi-axial random vibration experiments were performed at different acceleration inputs (10, 20, 30, 40, 50, 60, and 70 Grms) within a frequency band of 10–5000 Hz. During the vibration tests, we conducted observations of vibration behaviour. After the vibration tests, we observed the fracture surfaces of the specimens using a scanning electron microscope. The results show that the fatigue fracture was due to the bending resonance mode for the given shape and dimensions of the specimens used in this study. In addition, cracks initiated at different areas on the fracture surface and later propagated; subsequently, the cracks coalesced. Finally, we discussed whether the fatigue life of materials subjected to vibration can be predicted using finite element analysis.

A Concept of Thermographic Method for Non-Destructive Testing of Polymeric Composite Structures Using Self-Heating Effect.

Traditional techniques of active thermography require an external source of energy used for excitation, usually in the form of high power lamps or ultrasonic devices. In this paper, the author presents an alternative approach based on the self-heating effect observable in polymer-based structures during cyclic loading. The presented approach is based on, firstly, determination of bending resonance frequencies of a tested structure, and then, on excitation of a structure with a multi-harmonic signal constructed from the harmonics with frequencies of determined resonances. Following this, heating-up of a tested structure occurs in the location of stress concentration and mechanical energy dissipation due to the viscoelastic response of a structure. By applying multi-harmonic signal, one ensures coverage of the structure by such heated regions. The concept is verified experimentally on artificially damaged composite specimens. The results demonstrate the presented approach and indicate its potential, especially when traditional methods of excitation with an external structure for thermographic inspection cannot be applied.

Enhancing acoustic signal response and absorption of an underwater coated plate by embedding periodical inhomogeneities.

An underwater structure is proposed for simultaneous detection and stealth purposes by embedding periodic signal conditioning plates (SCPs) at the interface of two elastic coatings attached to an elastic plate. Results show that the embedded SCPs can enhance sound absorption at frequencies below the coincidence frequency of the plate (fc). Significantly enhanced absorption occurs at five peaks, of which the peak due to excited localized bending resonance in the outer coating between SCPs is the most significant. When the dilatational velocity of the outer coating equals that of the inner coating, nearly total absorption occurs in a wideband, owing to strong coupling between the localized waveguide resonance in the outer coating and that in the inner coating, and the diffraction waves by the SCPs. Meanwhile, an amplified acoustic signal of over 14 dB is observed at most frequencies within 0 ∼ fc at the coatings' interface close to the SCPs' edges, owing to focused stress formed there. Peaks in the signal response at maximal 30 dB are also observed. These peak frequencies are coincident with or close to the peak frequencies of absorption, demonstrating that significantly enhanced acoustic signal and absorption can be achieved simultaneously through the use of embedded periodic SCPs.

Experimental investigation into the mechanism of the polygonal wear of electric locomotive wheels

ABSTRACTExperiments were conducted at field sites to investigate the mechanism of the polygonal wear of electric locomotive wheels. The polygonal wear rule of electric locomotive wheels was obtained. Moreover, two on-track tests have been carried out to investigate the vibration characteristics of the electric locomotive's key components. The measurement results of wheels out-of-round show that most electric locomotive wheels exhibit polygonal wear. The main centre wavelength in the 1/3 octave bands is 200 mm and/or 160 mm. The test results of vibration characteristics indicate that the dominating frequency of the vertical acceleration measured on the axle box is approximately equal to the passing frequency of a polygonal wheel, and does not vary with the locomotive speed during the acceleration course. The wheelset modal analysis using the finite element method (FEM) indicates that the first bending resonant frequency of the wheelset is quite close to the main vibration frequency of the axle box. The FEM results are verified by the experimental modal analysis of the wheelset. Moreover, different plans were designed to verify whether the braking system and the locomotive's adhesion control have significant influence on the wheel polygon or not. The test results indicate that they are not responsible for the initiation of the wheel polygon. The first bending resonance of the wheelset is easy to be excited in the locomotive operation and it is the root cause of wheel polygon with centre wavelength of 200 mm in the 1/3 octave bands.

A novel piezoelectric actuator with two operating modes

A novel piezoelectric actuator with two operating modes is proposed and tested in this work, whose unique feature is that it has different mechanical output performances under two bending resonance frequencies. The proposed actuator is fabricated by bonded eight pieces of lead zirconate titanate ceramic plates on an aluminum alloy beam symmetrically. When the ceramic plates are excited by signals with resonance frequency of the first bending mode of the actuator, two bending vibrations will be superimposed to form elliptical movements on the two driving tips, which is the first operating mode. The other operating mode can be realized easily by changing the working frequency to the second bending mode of the actuator. These two operating modes are calculated and compared in detail. The prototype achieves a maximum no-load speed of 171 mm/s and maximum thrust force of 0.6 N using the first operating mode, whereas these two values are increased to be about 208 mm/s and 0.76 N under the second operating mode. The weight of the proposed piezoelectric actuator is about 17.7 g, and the maximum force weight ratio is tested to be about 42.9 N/kg.

10.32: Experimental study on high temperature elastic modulus of China made high strength structural steel

ABSTRACTHigh strength structural steel (HSSS) has better economic and environmental benefits than mild structural steel, and becomes more popular in the building construction projects. The current codes for fire safety design of steel structures is mainly developed based on the test data from mild structural steel and might be not applicable to the high strength structural steel. This paper reports an experimental study on the high temperature elastic modulus of China made high strength structural steel. Both static and dynamic test methods were used to determine the elastic modulus of Q550, Q690 and Q890 China grade steel at temperatures ranging from 20 °C to 800 °C. Suspended coupling bending resonance method was used to measure the dynamic elastic modulus. The reduction factors of elastic modulus from test data were compared with the reduction factors determined by current codes, including the Chinese code CECS200, the Eurocode 3, the American code AISC and the Austrian code AS4100, and by other researchers. The study found that unlike the static reduction factors (reduction factors determined by the static method) the dynamic reduction factors are not sensitive to the steel grade. The static elastic modulus is greater than the dynamic elastic modulus at low temperatures and is less than the dynamic modulus at high temperatures. Both the static and dynamic reduction factors of HSSS are greater than the elastic modulus reduction factors employed by the current codes. Design equation for dynamic elastic modulus of HSSS was derived from curve‐fitting of the test data.

High-cycle fatigue performance of high-mast illumination pole bases with pre-existing cracks

This paper presents the results of high-cycle fatigue testing of high-mast illumination poles (HMIPs) with pre-existing cracks at the pole-to-base plate connection detail. Resonant bending fatigue tests were conducted on five pairs of HMIP base specimens at nominal stress ranges of 41.4MPa (±20.7MPa), 27.6MPa (±13.8MPa), 20.7MPa (±10.3MPa) and 6.9MPa (±3.4MPa). The length and depth of pre-existing cracks was measured and the propagation of the individual crack was monitored throughout the testing using an ultrasonic inspection technique. The experimental results suggested that the fatigue lives of the tested specimens can exceed the predicted life for AASHTO fatigue category E details and approach category D details even in the presence of pre-existing cracks. The results provide insight into the fatigue response of HMIP with pre-existing cracks at the base connections at very low stress ranges and high cycle counts. The findings suggest that the pre-defined constant amplitude fatigue limits for AASHTO details may not strictly apply to HMIP details with pre-existing cracks.