Vibration Cycle Research Articles

Analysis of Mechanical Fatigue Behavior for MEMS Structures

Fatigue of MEMS structures may occur after cyclic vibration loading, which can lead to the material degradation. A test bench was built for mechanical fatigue testing, especially for the structures that actuated by electrostatic force. A RF MEMS switch which was made of gold was tested; the material mechanical characteristic was monitored during the tests by means of the value of pull-in voltage, which is related to the change of the Youngs modulus. The fatigue stress was produced by an alternating voltage, and the amplitude of which is from 15V to 65V. The excitation frequency and the actuation time were used as a counter for the number of cycles. The results show that there is no detectable mechanical fatigue after actuation up to one billion cycles.

Sensitivity of Combustion Driven Structural Dynamics and Damage to Thermo-Acoustic Instability: Combustion-Acoustics-Vibration

The dynamic combustion process generates high amplitude pressure oscillations due to thermo-acoustic instabilities, which are excited within the gas turbine. The combustion instabilities have a significant destructive impact on the life of the liner material due to the high cyclic vibration amplitudes at elevated temperatures. This paper presents a methodology developed for mechanical integrity analysis relevant to gas turbine combustors and the results of an investigation of the combustion-acoustics-vibration interaction by means of structural dynamics. In this investigation, the combustion dynamics was found to be very sensitive to the thermal power of the system and the air-fuel ratio of the mixture fed into the combustor. The unstable combustion caused a dominant pressure peak at a characteristic frequency, which is the first acoustic eigenfrequency of the system. Besides, the higher-harmonics of this peak were generated over a wide frequency-band. The frequencies of the higher-harmonics were observed to be close to the structural eigenfrequencies of the system. The structural integrity of both the intact and damaged test specimens mounted on the combustor was monitored by vibration-based and thermal-based techniques during the combustion operation. The flexibility method was found to be accurate to detect, localize, and identify the damage. Furthermore, a temperature increase was observed around the damage due to hot gas leakage from the combustor that can induce detrimental thermal stresses enhancing the lifetime consumption.

The rising motion of grains in a vibrating pipe

The rising motion of grains in a vibrating pipe is studied experimentally and by DEM (discrete element method) simulations. A pipe is partially inserted into a static granular layer. With the pipe initially filled with a certain height of grains, when the pipe is set into vertical vibrations, grains in the pipe will rise along the pipe and the motion will be finally stabilized at a certain height. The rising height and the speed of motion are strongly dependent on the vibration strength. By using a high speed camera and through DEM simulation, the trajectory of individual grains and the force acting on the grains in each vibration cycle can be obtained. A force-based mechanism for this rising motion is proposed. During vibrations of the pipe, the grains in the pipe are compacted and loosened alternately, and the force of the pipe and the grains varies periodically, thus leading to the rising motion of grains. A new possible way of continuously transporting grains is presented in this work.

Fractal Theory and Contact Dynamics Modeling Vibration Characteristics of Damping Blade

The contact surface structure of dry friction damper is complicate, irregular, and self-similar. In this paper, contact surface structure is described with the fractal theory and damping blade is simplified as 2-DOF cantilever beam model with lumped masses. By changing the position of the damper, lacing and shroud structure are separately simulated to study vibration absorption effect of damping blade. The results show that both shroud structure and lacing could not only dissipate energy but also change stiffness of blade. Under the same condition of normal pressure and contact surface, the damping effect of lacing is stronger than that of shroud structure. Meanwhile, the effect on changing blade stiffness of shroud structure is stronger than that of lacing. This paper proposed that there is at least one position of the blade, at which the damper dissipates the most vibration energy during a vibration cycle.

正弦振动对航空相机成像影响的分析与验证

The imaging resolution of aerial camera is limited by vibration during exposure. Dynamic modulation transfer function is used to study the impact of the sinusoidal vibration on imaging. Modulation transfer function (MTF) of high-frequency and low-frequency vibrations are analyzed through the calculation method based on spatial domain. When exposure time is not equal to an integer multiples of the vibration cycle, the impact of high-frequency vibrations on image quality is also random, but the randomness is less apparent than low-frequency vibration. The fast steering mirror is used to simulate vibrations, complementary metal oxide semiconductor (CMOS) sensor is used to capture images, wavelet transform is used to extract high frequency information. Exposure time is set to 20 ms, when the vibration frequency is 50 Hz, the fluctuation range of high-frequency information is only 0.0582104, which can be ignored compared with the total number of high-frequency information. When the vibration frequency is 15 Hz, the fluctuation range is 0.6233104 and randomness is obvious. But when the vibration frequency is 65 Hz, the fluctuation range is 0.1245104 and randomness is not obvious. By the correspondence between high-frequency information and MTF, the correctness of theoretical analysis is proved. On the basis of theoretical analysis and experiments, the general conclusion of sinusoidal vibration's effect on imaging is summed. This conclusion can not only be used to analyze the design of the imaging system structure, but also can be applied to image deblurring.

Elliptic vibration-assisted cutting of fibre-reinforced polymer composites: Understanding the material removal mechanisms

This paper develops an elliptic vibration-assisted (EVA) technique to effectively cut fibre-reinforced polymer (FRP) composites using a simple tool. A novel vibrator was invented to work at the anti-resonant frequency to realize stable and high variational velocities. A three-dimensional microstructure-based finite element model was also established to explore the material removal mechanisms in the EVA cutting. It was found that the application of vibration can significantly decrease the cutting forces and reduce the subsurface damage in a workpiece. The vibration in the cutting direction is more effective in reducing the cutting force, but that normal to the cutting direction has the advantage of chip removal. When the vibration is applied to both the directions in the EVA cutting, an optimal cutting process can be reached, providing much smaller cutting forces, a much improved surface integrity, and an extended tool life. The study concluded that the ratio of the tool-feed-rate to the maximum vibration velocity in the cutting direction, and the ratio of the cutting distance in a single tool vibration cycle to the fibre diameter are the key parameters. To maximise the advantage of the EVA cutting, it is necessary that these two parameters are below their critical values.

Numerical simulation ultrahigh waterjet (WJ) flow field with the high-frequency velocity vibration at the nozzle inlet

This paper presents an investigation of ultrahigh pressure waterjet (WJ) flow field with the high-frequency velocity vibration at the nozzle inlet by computational fluid dynamics method. The velocity field of the flow inside the WJ nozzle is obtained. The influence of vibration parameters, such as amplitude and frequency on the flow field are studied. The results of investigation indicate that the flow velocity at the WJ nozzle outlet has almost the same vibrating type with the inlet velocity vibration. During a vibration cycle, the velocity field of the flow is changing greatly. The serials value of the vibration frequency and amplitude are taken to test their influence on the flow field. The simulation results show that the flow field also changes greatly with the different frequency and amplitude. Based on the obtained results, the mechanism of system pressure vibration influence on the water jet flow field inside the WJ nozzle is obtained, and a new method is provided to optimize the machining process with the aim to improve the machine efficiency and surface quality of the work piece.

Flow past tandem cylinders under forced vibration

Flow past two cylinders in tandem arrangement under forced vibration has been studied experimentally employing the hydrogen bubble visualization technique. The Reynolds number, based on the cylinder diameter, is fixed at Re=250. In stationary state of the two cylinders with P/D=2.0, dual vortex shedding frequencies fL (St=0.14) and fH (St=0.18) are identified. fL is associated with the shear layer reattachment behavior and fH is related to the single bluff body behavior. Under a variety of forced vibrations of the two cylinders at a fixed vibration amplitude A/D=0.25, diverse and highly-repetitive vortex patterns are yielded. They are classified into two typical modes—a low-frequency mode and a high-frequency mode. The two modes are represented by two vortex patterns yielded from in-phase vibration of the two cylinders with P/D=2.0 and at vibration frequencies fe≈fL and fe≈fH. The difference between the two modes is on the number of vortices formed per vibration cycle. For the low-frequency mode, the number is four; for the high-frequency model, it is two. In both modes, the vortex formation is phase-locked to the cylinder motion. For a specified mode with a fixed vortex number per cycle, the way the vortices evolve in the wake can be somewhat different by changing the vibration frequency, pitch ratio, as well as the vibration type. These affecting factors have been examined in this work, and the associated vortex patterns have been characterized and compared.

How the ideal jamming point illuminates the world of granular media

The zero temperature properties of frictionless soft spheres near the jamming point have been extensively studied both numerically and theoretically; these studies provide a reliable base for the interpretation of experiments. However, recent work by Ikeda et al. showed that, in a parameter space of the temperature and packing fraction, experiments to date on colloids have been rather far from the theoretical scaling regime. An important question is then whether theoretical results concerning point-J are applicable to any physical/experimental system, including granular media, which we consider here. On the surface, such a-thermal, frictional systems might appear even further from the idealized case of thermal soft spheres. In this work we address this question via experiments on shaken granular materials near jamming. We have systematically investigated such systems over a number of years using hard metallic grains. The important feature of the present work is the use of much softer grains, cut from photoelastic materials, making it possible to determine forces at the grain scale, the details of the contact networks and the motion of individual grains. Using this new type of particle, we first show that the contact network exhibits remarkable dynamics. We find strong heterogeneities, which are maximum at the packing fraction ϕ*, distinct from and smaller than the packing fraction ϕ(†), where the average number of contacts per particle, z, starts to increase. In the limit of zero mechanical excitation, these two packing fractions converge at point J. We also determine dynamics on time scales ranging from a small fraction of the shaking cycle to thousands of cycles. We can then map the observed system behavior onto results from simulations of ideal thermal soft spheres. Our results indicate that the ideal jamming point indeed illuminates the world of granular media.

Approach on the Life-Prediction of Solder Joint for Electronic Packaging Under Combined Loading

A life-prediction approach of solder joints for electronic packaging under combined loading is presented in this paper. The deformations of solder joints are calculated under vibration and thermal cycling loading based on the finite element method. The calculated results are used as the boundary condition of the multi-axial loading to investigate the strain and stress of the solder joints. Then the life of solder joints can be evaluated by using a linear damage superposition approach. The result reveals that the life of solder joints can be divided into three regions according to the vibration amplitude at the same temperature: the life of solder joints in the first region is affected by creep damage; the life of solder joints in the second region is greatly influenced by the combined loading damage; the life of solder joints in the third region is impacted by the fatigue damage. The trend of the simulation results approximately agrees with the experimental results of other researchers.

Experimental and analytical study of the elliptical vibration-assisted turning process with the dynamic friction model

A novel analytical model for prediction of forces in elliptical vibration-assisted turning using a dynamic friction model is presented in this article and verified with experimental elliptical vibration-assisted turning tests. In elliptical vibration-assisted turning process, the main cause of force reduction is the reversal of the friction force direction in a fraction of vibration cycle time. In analytical modeling of elliptical vibration-assisted turning, the change of the relative sliding velocity direction causes a stick–slip condition which cannot be detected with static friction models like Coulomb model. In this research, a dynamic friction model, named LuGre model, is used to predict the machining forces in elliptical vibration-assisted turning. To derive the model coefficients, a series of orthogonal cutting experiments are performed on Al 6061, Al 7075 T6, Copper and Inconel 718, and the friction coefficients are identified using genetic algorithm optimization method. The cutting forces are determined by incorporating the friction forces calculated from LuGre model. To verify the results, a series of elliptical vibration-assisted turning experiments are performed on four above-mentioned workpiece materials using an elliptical vibration-assisted turning tool. The machining forces are then compared with the analytical results. The results achieved from the analytical solution using LuGre dynamic friction model are in a good agreement with experimental results.

Seismic Response Analysis of the Semi-Floating System of Long Span Cable-Stayed Bridge

According to the seismic performance of cable-stayed bridge with a project example, using finite element analysis method, establishing the space beam element and link element calculation model, the dynamic characteristic and the seismic response of the cable-stayed bridge with selected three earthquake waves were calculated, the results were compared with the of the response spectrum method.The results show that:the semi-floating system of cable-stayed bridge is great flexibility, the vibration cycle is generally longer; the results by using the response spectrum method are smaller; the cable-stayed bridge should be calculated in accordance with the specific circumstances of the project with multiple seismic waves.

Failure Analysis of Board-Level Sn-Ag-Cu Solder Interconnections Under JEDEC Standard Drop Test

This work investigates the board-level drop reliability of printed circuit boards (PCBs) assembled using three chip-size packages subjected to Joint Electron Device Engineering Council (JEDEC) standard drop test condition B. The acceleration and dynamic strain responses at several locations of the board-level package in the time and frequency domain are comprehensively investigated. The results in the time domain suggest that the dynamic response of the board-level package has two phases: forced vibration and free vibration. The maximum response occurs at the first half free vibration cycle. The acceleration response at the center of the PCB is larger than at the edges, whereas the dynamic strain response is just the opposite. The results in the frequency domain show that the first mode is fundamental. In addition, failure analysis is performed using the dye-and-pry test and cross-section test, suggesting that the brittle cracking occurs at the layer between the integrated circuit (IC) pad and the solder, not only through intermetallic compound (IMC) but also along the surface between the IC pad and IMC.

A novel universal joint with PZT-driven cyclic symmetric stator

Rotary actuation generated by a cyclic symmetric stator vibrations have been investigated in this research by using numerical finite elements. The cyclic symmetric stator’s vibration response is characterized through parameter studies with varying number of protrusion fingers, their geometry parameters and contact angle between stator fingers and rotor. The structure responses on the stator disk and protrusion finger of the stator have been experimentally validated in this study. The split-frequency structure vibration response on the protrusion fingers has been found to be catalogued by the number of the finger on the stator disk. The radial deformation of the protrusion finger was examined and characterized by two different parameters, namely the displacement strength and the bending deformation angle. The numerical studies in this research were validated by experimental mechatronic prototype, from which good agreement between the two and consistency between prediction and measurement were found.

Using Vocally Inspired Mechanical Conditioning to Enhance the Synthesis of a Cell-derived Biomaterial

The collection of cell-derived extracellular matrix (ECM) to form implantable biomaterials has therapeutic potential. However, a significant challenge to the creation of these biomaterials is the ability to produce an adequate quantity of ECM from cells in culture. Mechanical stimulation has long been viewed as a practical means to enhance cellular matrix production. In this study we explored the influence of vocally inspired mechanical stimulation, a unique combination of high frequency vibration and low frequency strain, on the production of ECM. Using a custom fabricated vocal bioreactor, tracheal fibroblast seeded sacrificial foams were treated for 3weeks using either isolated cyclic strain, combined cyclic strain and vibration (dual mode), or static conditioning. When compared to static controls, ECM production was significantly increased for samples conditioned with either cyclic strain or dual mode stimulation. The quantity of ECM harvested from sacrificial foams increased from 25±1mg for statically conditioned control foams, to 34±3 and 52±10mg for cyclic strain and dual mode conditioned samples respectively. Furthermore, mechanical conditioning significantly increased the elastic modulus of ECM biomaterials collected from sacrificial foams. Static control modulus increased from 40±2 to 63±7kPa and 92±7kPa following isolated cyclic strain and dual mode conditioning, respectively. These results indicate that cyclic strain conditioning can be used to accelerate the production of ECM by human tracheal cells during growth in culture, and that the addition of high frequency vibration to the conditioning program further enhances ECM production.

Performance and reliability of new CMUT design with improved efficiency

The performance and reliability issues of a new capacitive micro-machined ultrasonic transducer (CMUT) are presented in this paper. To enhance the moving efficiency, by obtaining a piston-like motion, an indirectly clamped membrane structure is proposed. The CMUT with indirectly clamped membrane is composed of three parts which are a circular moving plate, a ring-shaped bridge layer and an upper plate. By connecting circular moving plate to upper plate vertically through a ring-shaped bridge layer, this new structure was expected to produce the piston-like and more flexural motion. It also exhibited 1.7 times higher output pressure and 14.7% wider fractional bandwidth when compared to conventional basic structure. Environmental tests were carried out to verify the robustness and resistance to stress from temperature and humidity. For device's durability and lifetime estimation, an accelerated long-term operating test has also been performed. The derived mean time to failure (MTTF) was more than 2.29×1011 vibration cycles, which translates to about 2650h of guaranteed operational time.

Aeroelasticity at Reversed Flow Conditions—Part III: Reduction of Surge Loads by Means of Intentional Mistuning

Compressor surge consists of four phases: (i) pressure rise, (ii) flow breakdown, (iii) blow-down, and (iv) flow recovery. During the blow-down phase reversed flow conditions exist, where a blade may accumulate hundreds of vibration cycles, depending on the surge volume and the vibration frequency. High vibration amplitudes and blade damages were observed in the past. In Part I (GT2011-45034) a compressor cascade was analyzed experimentally and analytically at steady reversed flow conditions. It has been shown that (i) the steady flow field can be predicted well by CFD analysis, (ii) the overall damping coefficient calculated by unsteady CFD compares reasonably well with measurements, and (iii) a blade may become unstable at certain reversed flow conditions. In Part II (GT2011-45035) the analytical procedures used in Part I were applied to the front part of a multistage HPC for reversed flow conditions. It was found that surge loads consist in reality of two physically different phenomena (i) the pressure wave during the flow breakdown leading to rather low blade stresses and (ii) flutter during the blow-down phase which may lead to very high blade stresses and damages during surge for some stages. As it is well known that intentional mistuning is a way to mitigate flutter, intentional mistuning is investigated in Part III of the paper at reversed flow conditions. At first, a CFD study of a single airfoil is presented showing the dependency of aerodynamic damping upon flow angle and pressure ratio over the airfoil at reversed flow conditions, including intentional mistuning studies. Secondly, an investigation is presented which shows experimentally and analytically that surge stresses can be reduced significantly by the use of intentional mistuning. In a multistage compressor test rig, one rotor stage, which experienced very high stresses during surge, was subjected to a cutback on every second blade, leading to significantly reduced surge stresses. Analytically, an aeroelastic eigenvalue analysis showed the same behavior.

Modeling pulse-like lip vibrations in brass instruments

During the starting transient of a note on a brass instrument it can take several cycles of lip vibration before acoustics reflections from the end of the instrument can influence the lip frequency. Under certain conditions, the lip may fail to oscillate at the pitch of the air column resulting in an unwanted pulse-like waveform with relatively low repetition rates (similar to the vocal fry register of phonation in the human voice). This is often observed in the playing of beginners if the lips are insufficiently tense or if the top and bottom lips overlap to a large extent. In this study, the reasons for this behavior will be investigated using modeling techniques with the aim of improving the agreement between physical models and measured transients by including the forces responsible for this effect.

Describing alternative articulations of the Spanish trill /r/ by ultrasound technology

The Spanish trill /r/ is typically described as having a single realization—that is, as the result of aerodynamic forces operating on a tongue tip/blade constriction placed midsagittally in the dental, alveolar, or postalveolar place of articulation, in such a way that air channels along the sides of the tongue open and close for multiple cycles of vibration. As with American English /ɹ/, this sound is acquired late by typically developing children and is frequently an element in articulatory disorders. As with American English /ɹ/, perceptually equivalent “correct” trill /r/’s may be realized differently by different speakers. Knowledge of these alternate “correct” realizations would clearly be helpful to clinicians and learners of Spanish. In this preliminary study, we report data from ultrasound images of individuals who speak different dialects of Spanish. Preliminary data suggests there are at least two different articulatory postures used when producing the Spanish trill /r/, one of which involves lateralization. These articulatory differences do not affect what native listeners categorize as perceptually correct Spanish trills.

Mode competition in streamwise-only vortex induced vibrations

Time-resolved Particle-Image Velocimetry (PIV) has been used to study mode competition and transient behaviour in the wake of a cylinder experiencing Vortex-Induced Vibrations (VIV) in the streamwise direction. The cylinder response regime contained two branches, occurring above and below the onset of synchronisation between the wake and the cylinder motion (lock-in). During the first branch, the wake exhibited both the S-I mode (in which two vortices are shed simultaneously per vibration cycle) and the alternate A-II mode (similar to the well known von Kármán vortex street). An extended PIV data set acquired in this region revealed mode switching between the S-I and A-II modes. A criterion based on Proper-Orthogonal Decomposition was developed to identify which mode was dominant as a function of time. The A-II mode was found to be dominant for over 90% of the instantaneous fields examined, while the S-I mode appeared to be more unstable.Symmetrically shed vortices were found to rearrange downstream into an alternate structure in which the wake was no longer synchronised to the cylinder motion. The dominant frequency of transverse velocity fluctuations was measured throughout the wake in order to study the effects of this breakdown in more detail. For the majority of the wake, the fluctuations occurred at the Strouhal frequency, while in a region in the near wake the fluctuations occurred at the frequency of the cylinder motion. It is thought that during the first response branch vortices are formed at the cylinder response frequency, but tend to quickly rearrange downstream into an alternate structure which is no longer synchronised to the cylinder motion. As a result, the fluctuating drag will be synchronised to the structural motion, and is capable of providing positive energy transfer in the apparent absence of lock-in. Finally, the spatial dependence of the frequency of velocity fluctuations throughout the wake is used to explain some of the conflicting results in the literature regarding streamwise VIV, and the implications for the general study of VIV are discussed.