Low-amplitude Vibration Research Articles

Bond-pad damage in ultrasonic wedge bonding

Utilizing SEM/EDX analysis, microscale fracture at the bond-pad is detected when Cu wire is wedge bonded to a Cu or Al substrate. It is found that when a bond is fractured by pulling the wire similar to a pull test, a bulge on the wire and a cavity in the substrate are formed and fracture occurs in the original substrate. Using a 3D optical profiler, it is revealed that for a constant bond force and bond power, cavity's depth, radius, and surface area increase with bond time. These metrics are proposed as new factors for optimizing the wedge bonding process. A suitable combination of bonding parameters should maximize the cavity's surface area (as it pertains to bond's pull force) while minimizing the cavity's depth relative to the substrate's thickness to prevent damage in the substrate. Furthermore, employing Molecular Dynamics simulations, a possible plastic deformation mechanism for bond-pad damage is proposed. The mechanism points to the potential benefits of using a small-grain-sized substrate, a low transducer's vibration amplitude, and a high transducer's frequency for minimizing the cavity's depth.

Design and characterization of non-linear electromagnetic energy harvester with enhanced energy output

This paper presents design, analysis, and characterization of a compliant non-linear electromagnetic energy harvester operating on the principle of bi-stability incorporated with a displacement amplification mechanism. The energy harvester engenders energy from ambient vibrations at multiple modes and with frequencies ranging from 80 to 120 Hz. The energy harvester is analytically modeled using the mechanic’s elastic beam theory. Finite Element Analysis (FEA) has been carried out using commercial Finite Element Method (FEM) based software to perform static, fatigue, dynamic and electromagnetic analysis. Bi-stable mechanism has been used to harness energy at a wider frequency bandwidth while lever mechanism is acting as a displacement amplifier for enhancing low frequency vibration amplitude with the amplification factor of 6.24. With such amplification factor, the energy harvester can be deployed to extract vibrations of diminutive level and recast them into electrical energy in the form of generated voltage. Spring steel material, owing to its structural sensitivity, stiffness and higher value of ultimate stress, was used for its fabrication. The use of Neodymium (N52) magnets, copper coils and shaker were put into practice for testing of this device. The coil resistance is 2.5 Ω with number of turns kept at 350. The maximum output voltage of 1.86 V was generated at 106 Hz with root mean square value of 548 mV. Testing results are in accordance with the results obtained through simulations and thus useful electrical power of 11.1 mW can be generated from ambient vibrations at a wider bandwidth of 18 Hz with operating frequency ranging from 99 to 117 Hz.

Electric-Force Conversion Performance of Si-Based LiNbO3 Devices Based on Four Cantilever Beams.

In micron or nano smart sensing systems, piezoelectric cantilever beams are distributed as major components in microsensors, actuators, and energy harvesters. This paper investigates the performance of four cantilever beam devices with "electric-force" conversion based on the inverse piezoelectric effect of lithium niobate (LiNbO3, LN) single-crystal materials. A new compact piezoelectric smart device model is proposed, designed as a single mass block connected by four beams, where devices exhibit smaller lateral errors (0.39-0.41%). The relationship between the displacement characteristics of cantilever beams and driving voltage was researched by applying excitation signals. The results show that the device has the maximum displacement at a first-order intrinsic frequency (fosc = 11.338 kHz), while the displacement shows a good linear relationship (R2 = 0.998) with driving voltage. The square wave signals of the same amplitude have greater "electrical-force" conversion efficiency. The output displacement can reach 12 nm, which is much higher than the output displacement with sinusoidal excitation. In addition, the relative displacement deviation of devices can be maintained within ±1% under multiple cycles of electrical signal loading. The small size, high reliability, and ultra-stability of Si-LN ferroelectric single-crystal cantilever beam devices with lower vibration amplitudes are promising for nanopositioning techniques in microscopy, diagnostics, and high-precision manufacturing applications.

Effects of vibration conditions on thermo-hydrodynamic performances of oscillating heat pipes with various diameters

This paper investigates the thermo-hydrodynamic performance of oscillating heat pipes (OHPs) with different inner diameters (1.5 mm ~ 3.0 mm) under vibration conditions. The effects of vibration frequency (25 Hz, 50 Hz, and 100 Hz) and amplitude (0.4 mm, 0.8 mm, and 1.2 mm) on the startup and quasi-steady heat transfer of OHPs were analyzed. Results indicate that increasing vibration frequency promote fluid flow in OHPs, while increasing vibration amplitude has the opposite effect. The impact of vibration frequency and amplitude on hydrodynamic characteristics is more pronounced in OHPs with larger diameters due to additional forces induced by vibrations. The startup performance is firstly weakened and then gradually improved with the increasing vibration frequency, indicating the flow resistance is increased under low-frequency vibration condition. The initial fluid movement in the OHPs starts more easily under low-amplitude vibration condition, and thus the startup performance is optimum when the vibration amplitude is 0.4 mm. In addition, the startup performance of OHP with the inner diameter of 1.5 mm is affected mostly due to the finite fluid volume. The heat transfer performance, for the OHP with 3 mm inner diameter, will not be improved until the vibration frequency is higher than 100 Hz, and it is reduced most under the vibration amplitude of 0.8 mm.

Structural design of new mesh-type high-damping rail pad and comparative experimental study on the mechanical property with the traditional rail pads

Commonly used rail pads (RPs) in urban rail transit fastening systems comprise prismatic and grooved rail pads (PRP and GRP). This research introduced novel mesh-type and mesh-type high-damping rail pads (NMTRP and MTHDRP) to mitigate RP’s stress and enhance damping efficiency while optimizing elastic material utilization. A finite element model (FEM) of the fastening system was established and validated through stiffness and hammering tests of the RPs. The FEA results revealed that the mesh-type RP offered advantages in uniform stress distribution and efficient material usage. The MTHDRP has a significantly lower stress level than the PRP and GRP because of the damping block, it will prolong the MTHDRP’s service life. Both NMTRP and MTHDRP displayed reduced static and dynamic stiffness in comparison to PRP and GRP. Notably, MTHDRP demonstrated the lowest dynamic-to-static stiffness ratio at 1.45, indicating superior dynamic stiffness retention capacity relative to the other three RPs. The hammering test found that the MTHDRP exhibited the highest damping ratio among the four RPs and consistently lower vibration amplitudes in the time and frequency domains at the rail, clip, track bed, and ground when compared to the other RPs. Furthermore, analysis of the 1/3 octave frequency band of the acceleration signal underscored MTHDRP’s excellence, with vibration levels reduced by 4.31, 4.37, 4.21, and 1.43 dB at the rail, clip, track bed, and ground, respectively, in comparison to PRP. These findings affirm the superior vibration reduction performance of MTHDRP relative to the other three RPs and underscore its potential for enhanced foundation protection when incorporated into rail systems.

Experiment and simulation study on coarse aggregates settlement in vibrated concrete based on transparent granular suspensions

It is difficult to directly obtain the movement of coarse aggregates (CAs) since concrete is opacity. This paper mixes a transparent granular suspensions similar to fresh concrete for the vibration experiment, using white oil, silica powder, fused quartz sand and fused quartz stone. The vibration destroys the initial network structure of the granular suspensions causing the support force acting on CAs to decrease and CAs to rapidly accelerate sinking. Then, the granular suspensions gradually form a steady network structure making the support force increase as a logarithmic function and the sinking speed of CAs decrease. The variation law is combined with numerical simulation and concrete vibration experiments to obtain CAs settlement process in concrete with different vibration parameters. Under the same vibration frequency and different amplitudes, unit mass of concrete absorbs similar energy to reach the same distribution state of CAs and vibrated state, and this energy increases with the increase of vibration frequency. Therefore, the low-frequency and high-amplitude has higher construction efficiency than high-frequency and low-amplitude vibration. However, the high-frequency and low-amplitude vibration has larger range of optimal vibration time. The proposed method is helpful to better understand the settlement process of CAs and the energy can be used to evaluate the compactness and segregation state of vibrated concrete.

Temperature-Insensitive, Wide-Range Optical Fiber Vibration Sensor Based on Dispersion-Compensated Fiber

Vibration detection plays a vital role in the safety monitoring of engineering areas such as structural deformation of large buildings and railway tracks, and oil and gas spills. Herein, a temperature-insensitive optical fiber vibration sensor based on Mach-Zehnder interference is proposed and validated, which is achieved by utilizing a dispersion-compensated fiber (DCF). Specifically, single-mode fiber (SMF) is fused to both ends of a DCF to form an optical fiber vibration sensor, which is SMF-DCF-SMF (SDS) sensor. Under this sensing structure, this sensor’s vibration sensing characteristics, amplitude-frequency response, stability, repeatability and temperature-insensitive characteristics are investigated. The sensor can measure vibration frequency signals in the large frequency range of 0.1 Hz to 47 kHz by intensity demodulation. When the vibration frequency is 600 Hz, the maximum signal-to-noise ratio (SNR) of the sensor reaches 69 dB. In addition to that, the sensor can capture low amplitude vibration frequency signals down to 0.01 V. The proposed sensor has a wide measurement frequency range that effectively reduces temperature cross-sensitivity, and it has the advantage of being compact, low cost and easy to manufacture, with potential applications in health inspections, machinery and building saturation.

Optimization of biodiesel production, engine exhaust emissions, and vibration diagnosis using a combined approach of definitive screening design (DSD) and artificial neural network (ANN).

In this study, definitive screening design (DSD) optimization and artificial neural network (ANN) modelling techniques are applied for the production of palm oil biodiesel (POBD). These techniques are implemented to examine the vital contributing factors in achieving maximum POBD yield. For this purpose, seventeen experiments are conducted randomly by varying the four contributing factors. The results of DSD optimization reveal that a biodiesel yield of 96.06% is achieved. Also, the experimental results are trained in ANN for predicting the biodiesel yield. The results proved that the prediction capability of ANN is superior, with a high correlation coefficient (R2) and low mean square error (MSE). Furthermore, the obtained POBD is characterized by significant fuel properties and fatty acid compositions and observed within the standards (ASTM-D675). Finally, the neat POBD is examined for exhaust emissions and engine cylinder vibration analysis. The emissions results confirm a significant drop in NOx (32.46%), HC (40.57%), CO (44.44%), and exhaust smoke (39.65%) compared to diesel fuel at 100% load. Likewise, the engine cylinder vibration measured on top of the cylinder head reveals a low spectral density with low amplitude vibrations observed for POBD at measured loads.

Microvibration simulation of reaction wheel ball bearings

Microvibrations on board satellites are a well-known problem affecting their pointing accuracy by inducing oscillations to the line-of-sight. Fast rotating devices, such as reaction wheel assemblies (RWAs) are a major cause of these onboard mechanical disturbances. Imbalances in the flywheel, as well as imperfections in the ball-bearing components yield low-amplitude vibrations that are transmitted to the satellite structure, adversely affecting the performance of sensitive onboard instruments. This research focuses on the RWA’s ball bearing microvibration frequency and amplitude characterization. This is achieved by introducing specific geometry imperfections on the ball bearing rotating elements. In addition, variables such as the ball bearing preload, the number of balls and their dimensions are altered to understand how the bearing microvibration changes in order to minimize it. Finally, available physical microvibration test data is used to compare and cross-correlate the microvibration waterfall plots obtained from the transient FEA of the parametrized bearing models introduced herein. This work provides a better understanding of the relation between the main structural ball bearing parameters and the microvibration disturbances emitted by the RWA to minimize its mechanical noise.

Influence of vibration on droplet dynamics in a three-dimensional porous medium

In this study, the effects of vibration on droplet dynamics inside a three-dimensional (3D) porous medium are investigated with a focus on frequency, amplitude, and surface wettability. A lattice Boltzmann method based on the Allen–Cahn equation (A-C LBM) is used. The results show that the volume of the drained drop and drainage duration of the droplet are significantly affected by the contact angle. The hydrophilic nature of the pores causes the droplet to spread inside the medium and resist the vibration force, resulting in a lower discharged liquid volume and delayed drainage. In contrast, a hydrophobic surface repels the droplet and leads to quicker drainage. It is also observed that the speed of droplet drained from the porous medium is higher for hydrophobic conditions, causing the separated drop to rebound and jump back toward the medium after impacting the surrounding wall boundaries. A thorough investigation is conducted on the combined implication of the surface adhesion, amplitude, and frequency of vibration on the first separation time of the droplet from the porous medium and full drainage duration. The results show that with increasing the hydrophobicity, the required vibration amplitude for complete drainage has decreased. In this way, the interplay between the adhesive force and the vibration force impedes the liquid phase separation from the hydrophilic porous medium at a low vibration amplitude. However, the results demonstrate that even in these conditions, an increase in the vibration frequency can enhance the separation and improve the drainage of the liquid phase from the pores.

Plucking and linear-to-rotary hybrid harvester for low-amplitude vibrations of high-speed railway with an innovative three-step amplification mechanism

By harvesting the pervasive vibration energy, self-powered wireless sensor network (WSN) installed along the track can play an important role in structure health monitoring of high-speed railway. However, a considerable part of vibration energy of the rail is difficult to be harvested due to the characteristics of ultra-low frequency, small amplitude and large load. A hybrid frequency up-conversion energy harvester is designed and optimized in this paper aiming to address this critical problem. By utilization of a unique three-step amplification design for reducing inefficient transmission due to the possible gap of gear or ball-screw systems, high-efficient energy harvesting is realized for the small-amplitude excitation with both electromagnetic and piezoelectric conversion structures. The experiment results verify that the gapless amplification achieved by the flexible hinge structure as the first-step mechanism is effective for solving the gap issue. Compared with harvesters without the flexible hinges, the power is 250% higher under an excitation of low frequency (5 Hz) and ultra-small amplitude (0.3 mm). Moreover, based on the hybrid energy harvesting mechanism, more appreciable energy is obtained by introducing the plucking piezoelectric structure in addition to the electromagnetic unit.

Investigations into wetting and spreading behaviors of impacting metal droplet under ultrasonic vibration control

Ultrasonic-assisted metal droplet deposition (UAMDD) is currently considered a promising technology in droplet-based 3D printing due to its capability to change the wetting and spreading behaviors at the droplet-substrate interface. However, the involved contact dynamics during impacting droplet deposition, particularly the complex physical interaction and metallurgical reaction of induced wetting-spreading-solidification by the external energy, remain unclear to date, which hinders the quantitative prediction and regulation of the microstructures and bonding property of the UAMDD bumps. Here, the wettability of the impacting metal droplet ejected by a piezoelectric micro-jet device (PMJD) on non-wetting and wetting ultrasonic vibration substrates is studied, and the corresponding spreading diameter, contact angle, and bonding strength are also discussed. For the non-wetting substrate, the wettability of the droplet can be significantly increased due to the extrusion of the vibration substrate and the momentum transfer layer at the droplet-substrate interface. And the wettability of the droplet on a wetting substrate is increased at a lower vibration amplitude, which is driven by the momentum transfer layer and the capillary waves at the liquid–vapor interface. Moreover, the effects of the ultrasonic amplitude on the droplet spreading are studied under the resonant frequency of 18.2–18.4 kHz. Compared to deposit droplets on a static substrate, such UAMDD has 31% and 2.1% increments in the spreading diameters for the non-wetting and wetting systems, and the corresponding adhesion tangential forces are increased by 3.85 and 5.59 times.

VDDNet: An Object Detection Model for Measuring the Vibration Displacement of Rotating Structure

The signal acquisition and analysis of the structure vibration can effectively diagnose the operation status and fault type. The visual inspection method has the advantage of non-destructive testing and providing full-field vibration information for monitoring the vibration of rotating machinery. However, the accuracy requirements for measuring the small displacements generated by the low-amplitude vibration of high-speed rotating machinery are extremely high. It remains a challenge to achieve accurate, precise, and fast extraction of high-frequency and small-amplitude micro-vibrations using visual-based displacement measurement methods. Therefore, this paper proposes the object detection model, the Vibration Displacement Detection Network (VDDNet), for measuring vibration displacement of rotating bodies. VDDNet reduces the required computational complexity of the actual detection target and optimizes the quality of vibration displacement measurement. Additionally, by introducing an attention module and adopting different learning strategies to share rotating body target features, the real-time and accuracy of vibration monitoring are ensured. Furthermore, the evaluation method used in this paper comprehensively considers detection accuracy, real-time performance in deep learning methods, and displacement capture accuracy in vibration displacement monitoring. Actual vibration experimental results demonstrate that the proposed method is minimally affected by illumination and can achieve a better real-time capture accuracy of rotor micro-displacements, further proving its effectiveness and feasibility, which is helpful in advancing related research in this field.

A Bio-Inspired Bistable Piezoelectric Structure for Low-Frequency Energy Harvesting Applied to Reduce Stress Concentration.

Inspired by the two typical movement stages in the wingbeat cycle of a seagull in flight, a bio-inspired bistable wing-flapping energy harvester is proposed in this paper to effectively convert low-frequency, low-amplitude and random vibrations into electricity. The movement process of this harvester is analyzed, and it is found that it can significantly alleviate the shortcomings of stress concentration in previous energy harvester structures. A power-generating beam composed of a 301 steel sheet and a PVDF (polyvinylidene difluoride) piezoelectric sheet with imposed limit constraints is then modeled, tested and evaluated. The energy harvesting performance of the model at low frequencies (1-20 Hz) is experimentally examined, where the maximum open-circuit output voltage of the model reaches 11,500 mV at 18 Hz. With a 47 kΩ external resistance of the circuit, the peak output power of the circuit reaches its maximum state of 0.734 mW (18 Hz). When a full bridge circuit is employed to convert AC to DC, the 470 μF capacitor connected to it reaches 3000 mV at peak voltage after 380 s of charging.

Fractional nonlinear energy sinks

The cubic or third-power (TP) nonlinear energy sink (NES) has been proven to be an effective method for vibration suppression, owing to the occurrence of targeted energy transfer (TET). However, TET is unable to be triggered by the low initial energy input, and thus the TP NES would get failed under low-amplitude vibration. To resolve this issue, a new type of NES with fractional nonlinearity, e.g., one-third-power (OTP) nonlinearity, is proposed. The dynamic behaviors of a linear oscillator (LO) with an OTP NES are investigated numerically, and then both the TET feature and the vibration attenuation performance are evaluated. Moreover, an analogy circuit is established, and the circuit simulations are carried out to verify the design concept of the OTP NES. It is found that the threshold for TET of the OTP NES is two orders of magnitude smaller than that of the TP NES. The parametric analysis shows that a heavier mass or a lower stiffness coefficient of the NES is beneficial to the occurrence of TET in the OTP NES system. Additionally, significant energy transfer is usually accompanied with efficient energy dissipation. Consequently, the OTP NES can realize TET under low initial input energy, which should be a promising approach for micro-vibration suppression.

The drillstring dynamic time domains harmonic response and acceleration characteristics of compound drilling for the high-quality slim borehole

The harmonic response and acceleration characteristic of drillstring is established to improve borehole quality for the hydrogen underground storage (HUS). The harmonic response laws of drillstring is discussed. Harmonic response analysis includes non-failure case and failure case. Absorber control measure is simulated to lower vibration amplitude of drillstring. The drill string collides violently with the wellbore reduces the wellbore quality and increases the unreliability of the HUS. Lateral harmonic response has the greatest damage to well wall. Torsional harmonic response causes less damage than lateral vibration. High WOB (weight on bit) and high RPM (rotary per minute) are not conducive to the quality of HUS. In course of designing drilling parameter, it is required to avoid or reduce drillstring resonance under low-order inherent frequency as much as possible. The research result is of much significance to improve wellbore quality of hydrogen underground storage.

Effects of TiO2 nano-particles on wear-resistance and vibration-reduction properties of a polymer for water-lubricated bearing

Water-lubricated bearings play a vital role in improving the energy efficiency and environmental friendliness of ships. However, under the operating conditions such as start-stop and steering, the ship's stern bearing is often in boundary-lubricated or even dry friction condition due to the weak load-bearing capacity of the water film between the ship's drive shaft and the stern bearing. Therefore, the design of a polymer material with a low coefficient of friction and low vibration amplitude in both water-lubricated and dry friction conditions can greatly improve the stability and safety of the ship's operation. As a common reinforcing filler, TiO2 nanoparticles have a notable enhancement effect on the tribological properties of lubricants. Therefore, in this paper, the tribological behaviors between UHMWPE matrix reinforced with TiO2 nanoparticles and zirconia ceramic ball were investigated and the frictional vibrations during the friction process were analyzed. The results showed that TiO2 generated a ball-bearing effect on the surfaces of the friction pair, which led to a smooth and flat wear surface and reduced the friction and vibration behaviors. The modified composite with 0.9 wt% TiO2 exhibited the best tribological and vibration-absorbing properties in both water-lubricated and dry friction conditions. This study helps to provide a theoretical foundation for the design of marine water-lubricated bearing materials with excellent wear-resistance and vibration-reduction properties.

Mechanism of wear in zircaloy-4 under different loading conditions

Core components of nuclear reactor are generally made of zirconium alloys and some of them are prone to low amplitude vibration leading to material wear at contact interface. Reciprocating wear tests were conducted between zircaloy-4 (Zr-4) under dry and water-submerged conditions. To confirm the material transfer due to adhesion, wear tests were also conducted between Zr-4 and stainless steel. To understand the wear mechanism, worn surfaces were analyzed using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Coefficient of friction (COF) increases with increasing fretting duration and decreases with increasing frequency and displacement amplitude. Greater COF is observed under dry condition than that under submerged condition. The wear mechanism changes from adhesion to abrasion with increasing displacement amplitude.

Graphene/PVDF Nanocomposite-Based Accelerometer for Detection of Low Vibrations.

A flexible piezoresistive sensor was developed as an accelerometer based on Graphene/PVDF nanocomposite to detect low-frequency and low amplitude vibration of industrial machines, which may be caused due to misalignment, looseness of fasteners, or eccentric rotation. The sensor was structured as a cantilever beam with the proof mass at the free end. The vibration caused the proof mass to accelerate up and down, which was converted into an electrical signal. The output was recorded as the change in resistance (response percentage) with respect to the acceleration. It was found that this accelerometer has a capability of detecting acceleration up to 8 gpk-pk in the frequency range of 20 Hz to 80 Hz. The developed accelerometer has the potential to represent an alternative to the existing accelerometers due to its compactness, simplicity, and higher sensitivity for low frequency and low amplitude applications.

Vision-Based Dynamic Response Extraction and Modal Identification of Simple Structures Subject to Ambient Excitation

Vision-based modal analysis has gained popularity in the field of structural health monitoring due to significant advancements in optics and computer science. For long term monitoring, the structures are subjected to ambient excitation, so that their vibration amplitudes are quite small. Hence, although natural frequencies can be usually identified from the extracted displacements by vision-based techniques, it is still difficult to evaluate the corresponding mode shapes accurately due to limited resolution. In this study, a novel signal reconstruction algorithm is proposed to reconstruct the dynamic response extracted by the vision-based approach to identify the mode shapes of structures with low amplitude vibration due to environmental excitation. The experimental test of a cantilever beam shows that even if the vibration amplitude is as low as 0.01 mm, the first two mode shapes can be accurately identified if the proposed signal reconstruction algorithm is implemented, while without the proposed algorithm, they can only be identified when the vibration amplitude is at least 0.06 mm. The proposed algorithm can also perform well with various camera settings, indicating great potential to be used for vision-based structural health monitoring.