Higher Vibration Acceleration Research Articles

Dynamic characteristics and damage identification with interface damage of slabs in movable point crossing

As the operating density of China’s high-speed railway increases, the phenomenon of interlayer debonding in movable point crossing (MPC) is becoming more prevalent, which can lead to failure of the frog’s slab track. Meanwhile, vehicle impacts and interlayer debonding can exacerbate abnormal vibration of the vehicle and even lead to derailment. Therefore, based on the theory of rigid-flexible coupling dynamics, a vehicle-turnout-slab coupling dynamics model is established for the first time. In this model, the crossing rails with variable cross sections is considered and the interlayer debonding between turnout slabs is modelled by nonlinear springs. Then, the characteristics of the debonding is identified by applying a wavelet transform to the dynamic response of the vehicle. Finally, different types and sizes of debonding between the layers are considered. The results show that different debonding can lead to two types of contact, partial contact and complete voiding, which can further lead to detrimental effects on vehicle safety. And the limit of the defect size that causes the track slab to void is 1 mm. On this basis, it was found that when MPC’s slab tracks were voided, longer debonding can cause high frequency vibration acceleration of approximately 700 Hz in the vehicle axle box. The new insights obtained by this study could provide guidance for the maintenance period and avoid the development of the damage. This study not only obtained a mechanism for the effect of interlayer debonding on the dynamic response of the vehicle-track system, but also provides a theoretical basis of detecting interlayer debonding for future study.

Assessment of the impact of 3D printed water-lubricated cutless bearings material on vibration parameters.

The tested bearings were subjected to equal loads and rotational speeds, using water as the lubricant. Analysis showed that they achieved the best vibration damping at lower speeds, between 600 and 1100 rpm. Comparative studies of bearings made of different materials, such as available on the market bearings made of rubber, bearings printed with a 3D printer from PETG, PLA, ABS or Tribo filament materials, revealed differences in their vibration damping ability and operational stability. Conclusions from the study suggest that higher vibration acceleration may increase the radius of the trajectory, which may affect the function and performance of the bearings. The importance of the operational stability of water-lubricated plain bearings cannot be assessed solely on the basis of the RMS of vibration acceleration or trajectory radius. Both of these parameters are crucial from the user's point of view, especially in the context of various applications such as electric boats.

Vibration effect on Rayleigh–Taylor instability of sedimenting suspension

In this paper, the effect of vertical vibration on the Rayleigh–Taylor instability at the lower interface of a sedimenting suspension layer sandwiched between viscous fluids is studied numerically and theoretically. It is shown numerically that the vibration suppresses the amplitudes of interface perturbations and enlarges the widths of granular fingers, postponing the nonlinear growth stage. By modeling the suspension as a fluid with its effective density and viscosity, stability analyses are carried out, and the dominant growth rate and the dominant wave number predicted by the dispersion relation agree with the numerical results, especially for cases with strong vibrations. Because of the small-scale flow induced by the particles, high vibration acceleration amplitude and low vibration frequency, which correspond to a large vibration power input, increase the kinetic energy spectra at the high wave number regime, a phenomenon contrary to the vibration effect for pure fluid cases.

Vibro-fluidization of sand under coupled static loading and high-frequency cyclic loading

An increase in the operation speed of high-speed trains often leads to an increase in the loading frequency on subgrade soil. Hence, the long-term dynamic behavior of the subgrade and the service performance of high-speed tracks are affected. To determine the stress–strain characteristics of granular soil under high-frequency loading, a triaxial test setup was modified to investigate the effects of loading acceleration and duration, water content, vibration frequency, cell pressure, and initial soil density. The experimental results indicate that there are reductions in axial stress and volumetric strain during high-frequency loading. The reduction in axial stress is as high as 40%, and that of volumetric strain, which is permanent, could approach 0.1%. The stress reduction, strain compression, and excess pore pressure are found to vary linearly with vibration acceleration when a/g > 0.02, where a is vertical vibration acceleration and g is gravitational acceleration. The reduction in strength and strains are found to depend on the loading acceleration and effective cell pressure, but independent of the loading duration, water content, frequency, and initial density. A threshold acceleration a = 0.02g is observed, below which the changes in the shear strength and volumetric strain induced by vibration are negligible. At high vibration acceleration, the strain amplitude could increase, eventually leading to a collapse of the specimen.

Electrical Properties of Force Feedback Piezoelectric Actuator Using (Na,K)(Nb,Sb)O3–(Bi,Na)ZrO3 Ceramics

In this study, for developing the multilayer piezoelectric actuator, the (Na,K)(Nb,Sb)O3–(Bi,Na)ZrO3 ceramics were manufactured and their dielectric and piezoelectric properties were investigated. The manufactured ceramics showed the excellent physical properties: density = 4.56 g/cm2, kp = 0.47, Qm = 50, er = 1944, and d33 = 313 pC/N, suitable for piezoelectric actuator. The properties of the piezoelectric actuators are as follows: at the average size of 30.47 mm $$\times$$ 17.92 mm $$\times$$ 1.0 mm, resonance frequency fr = 69.87 kHz, anti-resonance frequency fa = 71.20 kHz, kp = 0.22, d33 = 1120 pC/N were appeared, respectively. The three piezoelectric actuators connected in parallel showed the high vibration acceleration of 2.0G at 580 Hz under 70 V, suitable for the force feedback actuator.

Using the Blood Coagulation Factors as a Predictor Component of the Occupational Vibration Exposure.

Background:Exposure to hand–arm vibrations higher than permissible standard rates can have destructing effects on workers’ health. Pneumatic hammers are among the tools that are used in civil and industrial projects, transferring high vibration acceleration to the workers. This study has considered the probable effects of hand–arm vibrations on the performance of blood coagulation factors in the workers using this tool and exposed to high vibration acceleration.Methods:Five new workers without any experience in exposure with hand–arm vibrations were selected for this interventional study. Blood sample was taken from each worker before they started working for the required analysis. Sampling was repeated in two other stages in 2-month intervals from the first sampling, whereas the workers were then experienced in working with pneumatic hammers. Measuring the vibration of the pneumatic hammer was done according to ISO 28927-10 standard.Results:The point of measuring the vibration acceleration was selected close to the hand, in accordance with the standard. Regarding the exposure time of the workers, the amount of vibration acceleration was obtained 15.54 m/s2. Activated partial thromboplastin times of four samples in the second and third stages have shown increases in comparison to the first stage in that respect. On the other hand, a number of red blood cells, white blood cells, and platelets did not show a consistent trend in the three stages.Conclusions:The considered samples showed longer time for blood coagulation as compared to the reference time. Thus, it can be concluded that the main reason is the acceleration in three different coordinate axes of x, y, and z. Hence, the values beyond permissible standard rate of hand–arm vibration in 8 h shifts affect the blood parameters, among which the considered coagulation parameters in this study showed more tangible changes in that respect.

An Exact Analytical Solution for Thermoelastic Response of Clamped Beams Subjected to a Movable Laser Pulse

The thermoelastic dynamic response of a clamped Bernoulli beam was studied when it was irradiated by a movable, temporally non-Gaussian, laser pulse. Both the energy absorption depth and the time decaying effects were considered. The temperature distribution, deflection, vibration acceleration, and stress of the beam were derived analytically, and the variations of them with time and space were illustrated. It was shown that the vibration frequency is independent of the scanning speed of the laser pulse. It is important to notice that, although the deflection of the beam is small, high vibration acceleration can be induced in microbeams, which is important for failure and fracture of the beam. Moreover, compressive stress is induced in the beam, but the importance of temperature-induced stress and deformation-induced stress may be different according to the duration time and moving speed of the laser pulse.

Measurement and analysis of hand-transmitted vibration of vibration tools in workplace for automobile casting and assembly

To investigate the features of hand-transmitted vibration of common vibration tools in the workplace for automobile casting and assembly. From September to October, 2014, measurement and spectral analysis were performed for 16 typical hand tools(including percussion drill, pneumatic wrench, grinding machine, internal grinder, and arc welding machine) in 6 workplaces for automobile casting and assembly according to ISO 5349-1-2001 Mechanical vibration-Measurement and evaluation of human exposure to hand-transmitted vibration-part 1: General requirements and ISO 5349-2-2001 Mechanical vibration-Measurement and evaluation of human exposure to hand-transmitted vibration-Part 2: Practical guidance for measurement in the workplace. The vibration acceleration waveforms of shearing machine, arc welding machine, and pneumatic wrench were mainly impact wave and random wave, while those of internal grinder, angle grinder, percussion drill, and grinding machine were mainly long-and short-period waves. The daily exposure duration to vibration of electric wrench, pneumatic wrench, shearing machine, percussion drill, and internal grinder was about 150 minutes, while that of plasma cutting machine, angle grinder, grinding machine, bench grinder, and arc welding machine was about 400 minutes. The range of vibration total value(ahv) was as follows: pneumatic wrench 0.30~11.04 m/s(2), grinding wheel 1.61~8.97 m/s(2), internal grinder 1.46~8.70 m/s(2), percussion drill 11.10~14.50 m/s(2), and arc welding machine 0.21~2.18 m/s(2). The workers engaged in cleaning had the longest daily exposure duration to vibration, and the effective value of 8-hour energy-equivalent frequency-weighted acceleration for them[A(8)] was 8.03 m/s(2), while this value for workers engaged in assembly was 4.78 m/s(2). The frequency spectrogram with an 1/3-time frequency interval showed that grinding machine, angle grinder, and percussion drill had a high vibration acceleration, and the vibration limit curve was recommended for those with a frequency higher than 400 min/d. The workers who are engaged in cleaning, grinding, and a few positions of assembly and use grinding machine, angle grinder, internal grinder, and percussion drill are exposed to vibrations with a high vibration acceleration and at a high position of the frequency spectrum. The hand-transmitted vibration in the positions of cutting, polishing, and cleaning in automobile casting has great harm, and the harm caused by pneumatic wrench in automobile assembly should be taken seriously.

Transparent and flexible haptic actuator based on cellulose acetate stacked membranes

The tactile sensation is the human interact with machines in the form of felt sensations in the hand or other parts of body skin. This paper presents a film type actuator for haptic feedback devices, based on electrostatic actuation of plasticized cellulose acetate stacked membranes actuator, which is fabricated and evaluated for suitability of haptic feedback devices. The stacked membranes actuator shows many promising properties such as high transparency, lightweight, wide range of actuation frequency and high vibration acceleration for instance. The actuator structure shows intense vibration acceleration due to several layers of stacked membranes associated with the intensified electrostatic attraction force between chargeable cellulose acetate membranes. Experiment for measuring vibrational acceleration was conducted over a wide frequency range and actuation voltage to prove actuator’s great potential application as tactile actuator of haptic feedback devices. In addition, the operating principle, fabrication method and performance measurements are explained in details.

Large-dynamic-range MEMS Electret Energy Harvester with Combined Gap-closing/Overlapping-area-change Electrodes

A novel in-plane MEMS electret energy harvester with combined electrodes of overlapping-area-change and gap-closing types is proposed for large output power both at low and high vibration accelerations. An early prototype has been successfully micro-fabricated with the single layer silicon-on-insulator process. Soft-X-ray charging is employed to establish uniform surface potential around 60 V on vertical electrets on the sidewall of the comb fingers. Up to 1.19 μW output power has been obtained at 552 Hz and 2.15 g acceleration oscillations, which corresponds to the effectiveness as high as 27.2%.

Transmission of whole body vibration in children while standing

Background Whole body vibration has recently been used as a therapeutic intervention for the treatment of children with disabling conditions. Researchers of these studies observed encouraging results; however, children may not be capable of attenuating high vibration accelerations to the head because of low mass. The purpose of this study was to determine if children transmit vibration differently than adults while standing on a vibration platform. Methods The experimental protocol required 11 children and 10 adults to stand on a commercially available vibration platform at progressively greater frequencies (28, 33, and 42 Hz). Transmissibility of vibration to various skeletal landmarks was assessed with a high speed motion analysis system. Findings Transmissibility in children was 42% and 62% greater than adults for the ankle and hip, respectively ( P = 0.03; effect size = 0.84–1.29). The values at the head were not different between groups ( P = 0.92) and remained 86% and 50% lower than values at the ankle and knee, respectively (effect size = 4.75–19.1). Interpretation Transmissibility of whole body vibration while standing is not markedly different between children and adults. In fact, the only differences are the transmissibility to the ankle and hip which are greater in children when the vibration platform is set at 33 Hz. More importantly, transmissibility to the head is not different between groups. These results do not suggest vibration therapy is safe as the biological response of children to acute or chronic acceleration impacts during whole body vibration is unknown.

Developments in laser Doppler accelerometry (LDAc) and comparison with laser Doppler velocimetry

This paper outlines the principles and early development of an interferometric technique for remote measurement of vibration acceleration — laser Doppler accelerometry (LDAc). One of the key advantages of LDAc over laser Doppler velocimetry (LDV) is its ability to measure extremely high vibration accelerations and shocks, effectively without limit, and this point is expanded upon in the paper. Early LDAc development showed how unwanted, velocity-dependent optical beats could occur on the photodetector but novel use of a frequency shifting device, whose primary purpose was for direction discrimination, was successful in isolating the required acceleration-dependent beat. A problem remained in the rate at which the velocity-dependent and acceleration-dependent beats broadened during target motion. In a further development, it was possible to 'select’ a back reflection to produce a velocity-dependent beat that was NOT modulated in the presence of target motion. The acceleration-dependent beat could then be demodulated and preliminary results are given to demonstrate this outcome.

Fracture energy during slicing of frozen meat by a vibrating knife

The force, and hence fracture energy, required to cut horse quadriceps muscle, using a knife which was vibrated in the direction of material feed, were measured over a range of temperatures (−1.5 to −32.5 °C), vibration frequencies (no vibration and 1 to 1000 Hz), accelerations (0.073 to 75 m s −2), thicknesses (0 to 40 μm off-cut), and direction to the muscle grain. High vibration accelerations (75 m s −2) resulted in reduction of the cutting force; the reduction was independent of the off-cut thicknesses and resulted from lowering the coefficient of friction between the vibrating blade and the frozen meat. Rows of ice formed by the blade showed that pressure melting of the ice around the cutting region occurred during cutting and suggested that a hydrodynamic lubricating layer of water reduced the friction of the vibrating blade.