Small Hammer Research Articles

Numerical Investigation of Evaluating the Degree of Damage in Concrete Plate Cold Joints through Surface Wave Dispersion Velocity Profiles

This study aims to develop a technology for assessing the interfacial condition of cold joints in concrete plates, focusing on the dispersion velocity profile of surface waves. The methodology employs a small impact hammer embedded with a piezoelectric element and a displacement receiver strategically positioned on either side of the seam. In this initial investigation, numerical models were constructed using ANSYS LS-DYNA. The cold joint zone was simulated by randomly removing elements with a predetermined void ratio. Displacement waveforms at the sensor node underwent analysis using a short-time Fourier Transform and the reassigned method to derive the dispersive velocity profile of surface waves. The study delves into the impacts of varying test-line lengths, impact durations, and void distributions. Numerical findings indicate that cold joints are detectable with a void ratio of 40% or greater. For the 60% and 80% void ratios, surface wave velocities register notably lower for wavelengths below 0.1 m and 0.2 m, respectively. Under the same porosity ratio for surface-observable cold joints, if their extension depth is smaller, the wave velocity on the dispersion curve will be lower than that of a fully penetrated cold joint. The current study reveals that a contact duration of 60 μs and an impactor-receiver distance of 0.82 m yield the most distinguishable results for detecting the extension and porosity ratio of a cold joint. Accompanied by tests with a hammer with a contact duration of 20 μs, additional information about the joint can be unveiled. Finally, various void distributions in the cold joint predominantly influence the wave velocity at shorter wavelengths.

Measured changes in the bridge mobility and radiativity of violins due to material creep following tensioning of strings

Violins have been observed to undergo a small, but measurable, deformation of the corpus after being brought into tune following a prolonged period without string tension. This behavior, which is analagous to the flexing of a bow, can be attributed to the viscoelastic properties of wood. Because of the relatively long time scale of deformation, the process is sometimes referred to as material “creep.” To assess the impact of creep on the sound of a violin, we measured the vibrational and acoustic response of multiple violins during this period of deformation. The measurement process involves tapping the bridge with a small modal impact hammer and recording the velocity response of the top plate using a laser Doppler vibrometer, as well as the far-field acoustic response in an anechoic chamber. Results show modest changes in the amplitude of the main body modes, most notably the CBR and B1- modes, and a consistent shift in the peak frequency of higher modes, over a two-day period after the strings were tuned.

Rapid assessment of fire damage to reinforced concrete structures using the surface wave method with contact and non-contact receivers

The study developed a rapid on-site assessment method for fire damage of reinforced concrete structures by using surface wave dispersion characteristics. A reinforced concrete slab containing four kinds of arrangement of steel-reinforced bars was cast. The gas furnace produced the fire damage by heating on one surface of the slab with a maximum temperature of 600˚C. The surface wave tests were carried out using an impact source and a receiver 0.5 m away from the impact location before and after the fire damage. The impactor is a small hammer embedded with a piezoelectric element to record the initial time of the impact. Contact and non-contact receivers were applied. The former is a displacement receiver, and the latter is a microphone. The surface wave response in the waveform was filtered out, and then processed by the short-time Fourier transform and reassigned method to obtain the group velocity spectrogram. The wave velocity-wavelength diagram of the surface wave was used for analysis. This study compares the results obtained by the two types of receivers before and after the fire. The influence of the relative directions between the survey line and the steel bars is also discussed. The results show that the test results obtained from the two types of receivers are similar under room temperature and 600˚C. However, the signal noise of the microphone is relatively large, and the consistency of repeated tests after a fire is poorer. The oblique angle between the measuring line and the steel bar is the most suitable choice because it can better distinguish the severity of fire damage and estimate the depth of deterioration.

Numerical Analysis of a Small Pneumatic Hammer Performance Based on Evaluation Method of Friction Force

Mechanical power loss in pneumatic hammers comes from the friction between parts in relative motion, and wear is among the failure mechanisms of the top hammer. Therefore, it is important for high performance and a longer service life of pneumatic hammers to reduce the friction force between parts in relative motion. This study presented a novel approach to quantitatively determine the friction force and consider it in the simulation model of pneumatic hammer. First, the friction force between piston and cylinder in a small pneumatic hammer was measured using an experimental setup at different inlet pressures. We could find from the experimental result that the friction force was about 0.8 N under the horizontal installation when there was no pressure supply, but it increased significantly, was 20 times greater than that without pressure supply, due to aerodynamic action by compressed air leaked from the annular gaps between the cylindrical matching surfaces of the components. In addition, it increased from 10.27 to 16.7 N due to an increase in inlet pressure and mechanical power loss in the pneumatic hammer that was about 10% of impact energy. Then, numerical analysis for a small pneumatic hammer performance was performed by a model considered the friction force using AMESim software. Finally, it can be seen from the simulation results that the proposed approach could significantly reduce the error between the simulated and the measured values for the impact energy because of ignoring the friction force. This approach will be used to predict service life of piston and find a low friction piston of pneumatic hammer in practical engineering.

Investigation of a noninvasive method for monitoring intracranial pressure using sheep skulls

It has been previously demonstrated that resonance frequencies of fluid-filled shells of simple geometry are shifted in proportion to fluid pressure [J.Acoust. Soc. Am. 131, EL506 (2012)]. We investigate the applicability of this approach for measuring changes of intracranial pressure in ovine skulls. A catheter inserted through the foramen magnum of a complete sheep’s head enables the control of hydrostatic pressure, which is measured independently using a pressure transducer inserted into the parenchyma through a drilled hole in the skull. The vibrational response is measured using a small modal impact hammer to gently tap the skull with small accelerometers mounted at different locations on skull. Acceleration normalized by impact force is computed in the frequency domain, averaged over multiple taps. Significant peaks in the response spectrum are identified and associated with vibrational modes observed using a laser Doppler vibrometer. The consistency with which peaks shift in frequency in proportion to ICP is reported. The effect of tap location and accelerometer placement is also explored.

A quantitative assessment of uncertainty in the measurement of violin impact response

It is a commonly stated belief among violin players and luthiers that new violins require a period of “playing in” for the tone to develop. Several studies have worked towards an answer to this question, such as measuring the change in tone according to the human ear or the vibrational response of stimulated wood. As the effects of sustained excitation on the mechanical response of violins will likely be subtle, it is necessary to create a consistent method of measurement and to quantify the expected range of deviation among repeated measurements. We measure admittance (velocity/force) by tapping the bridge with a small modal impact hammer and recording the velocity response of the top plate near the opposite side of the bridge using a laser doppler vibrometer. The acoustic response is also measured in an anechoic chamber. Since measurements of the same violin on different days do not produce identical response curves, several methods of characterizing the deviation were developed and compared. These uncertainty metrics will be used in the second phase of the experiment to determine the significance of the results, and ultimately work towards a better understanding of the effects of breaking in violins.

Using 3-D velocity contour plots to detect voids in grouted tendon ducts in post-tensioned concrete construction

3-D velocity contour plots are constructed to detect voids in grouted tendon ducts by a stress-wave test method requiring a receiver and a small instrumented hammer. Each time-domain waveform due to hammer impact is processed using the short-time Fourier transform to obtain the spectrogram (frequency-time relationship), which is enhanced using the reassignment method. The reassigned spectrogram is used to obtain the dispersion curve (velocity-wavelength relationship). The results from all test points are assembled to develop wave-velocity contour plots at different wavelengths. A wall specimen containing ducts with five different grouted conditions was constructed. Two types of test grids were used, namely latticed grids covering the entire wall surface and vertical grids directly above the ducts. For the former method, 3D contour plots of a large area can be constructed with few testing lines. For the latter method, the wave velocity contour plots can distinguish different grouting conditions. Finally, the wave velocity reduction to be expected for different grouting conditions and cover depth is provided.

A new stonefly from mid-Cretaceous Kachin amber reveals novel genital structure for the extinct genus Largusoperla (Plecoptera: Perlidae)

Largusoperla zhouchangfai sp. nov., a new extinct stonefly species is described based on a male adult in mid-Cretaceous Kachin amber. The new stonefly exhibits well-preserved wing pairs, dorsal and ventral abdominal segments and aedeagus. The new species is inter alia characterized by the two elongated lobes on the cleft tergum 10, inverted V-shaped epiproct sclerite, small circular hammer, subtriangular paraprocts, and the tubular aedeagus with three slender apical spines. Morphological characters of the new species are described, illustrated, and compared with related taxa.

A simulation between torque and angle with speed on robot mechanical arm of multibody systems

The effective factor has the turn of M1>M3>M2 in robotic arm. It has too turn 0.5m/s, 5º/s> 0.3m/s, 8º/s> 0.1m/s, 11º/s within conditions. That says that the speed is larger than angular speed about its effect to torque. The biggest torque happens at 5 º/s and 0.5m/s in first robot arm which is 500Nm. The least one is at 11 º/s and 0.1m/s in the third robot one which attains 80Nm. The turn of effective torque is small angular speed and hammer speed.

Teknik Pemotongan Kuku Sapi Pejantan Limousin

Limousin is one of the beef cattle breeds of the Taurus boss which was successfully devised and developed in France. In the maintenance of one of the management that is considered is care / nail cutting. Cutting is done to maintain performance while climbing teasher cow when semen collection process, avoid or prevent the nail grows abnormally, the limping leg, footrot (nail rot) and laminitis. The purpose of this paper is to describe the technique of cutting nails in Limousin bulls. Implementation methods of data collection by observation, interviews and secondary data collection. The process of cutting the nails using a cutting knife (kamagata teito), rennet, grinding, measuring bar, chisel, small hammer, hirauci rope (rope that has been done by packing). Mechanical cut your nails done by a process handling bulls of the cage toward the maintenance of cut nails, bulls put the nail cutting table (table hooves trimming), feet and body bound to the mast nail cutting table and cutting nails. Â

Comparison of Dispersion Image Resolution Acquired Using Multichannel Analysis of Surface Waves with Different Source Energy and Stacking

Active MASW method is a promising method to determine the stiffness characteristics of the subsurface strata. The accumulation energy to obtain high-resolution dispersion image depends largely on the energy generated from the active source. From the results obtained, the influence of different source energy, source plate and number of stacking on the dispersion image resolution were significant. Heavier source weight (e.g.7 kg sledgehammer) produced highamplitude energy band and provides even lower frequencies. However, if lighter source weight (e.g. small steel hammer) was used, it needs to be coupled with rubber plate to increase the low frequency content, thus generate deeper depth of investigation. Finally, the use of rubber plate and stacking increased the resolution of the dispersion image especially at lower frequencies by significantly suppressing the ambient noise.

Simple stress–strain model of very strong limestones and dolomites for engineering practice

This paper presents a simple mathematical model that can be used in engineering practice to estimate the stress–strain behavior of very strong limestones and dolomites (σc > 100 MPa) subjected to uniaxial compression. This model is developed using the canonical form of Haldane’s distribution function. To estimate the stress–strain response using the proposed model, sophisticated stiff load frames are not needed. It is argued that only a simple uniaxial tester (with a hand pump) for one point measurement at a small stress and Schmidt hammer are required to estimate stress–strain response from zero strain/zero stress up to failure.

Material Classification Based on Vibration Analysis

Abstract In this paper, we investigate the characteristics of an object’s vibration in identifying its material of construction. A simple vibration test is performed to classify different types of materials. The test is done by performing small hammer excitation on the object then recording its vibration using one acceleration sensor. Four different materials were tested (steel, hardwood, softwood, and plastic). The vibration signal was analyzed using MATLAB based model. The trained model was able to recognize the testing samples of each material. The advantages of this method are that it is accurate, fast and simple, can be performed on-site and is relatively inexpensive.

Violin surface velocities and radiativity

Complete surface velocity maps and radiativity measurements have been made of several violins of varying quality. The instruments were excited laterally at the top of the bridge with a small impact hammer, giving a strong signal up to 4 kHz. The wood velocities were measured with a 0.2 g accelerometer placed sequentially on a grid, all over the surface. The grid was small enough to allow a detailed look at the bridge island. The f-hole velocities were measured with a 6 mm diameter microphone at nine positions per hole, and the acoustic pressures were converted to velocities with a propagating wavefront model. The surface measurements were compared to radiation measurements made with a 92 cm radius microphone array in an anechoic chamber. The surface measurements could be completed in a day, the radiativities in two hours. The resulting maps of operating deflection shapes, calibrated in m/s per N, allow a detailed examination of the vibrational behavior of each instrument, at frequencies up to and including the first torsional mode of the bridge.Complete surface velocity maps and radiativity measurements have been made of several violins of varying quality. The instruments were excited laterally at the top of the bridge with a small impact hammer, giving a strong signal up to 4 kHz. The wood velocities were measured with a 0.2 g accelerometer placed sequentially on a grid, all over the surface. The grid was small enough to allow a detailed look at the bridge island. The f-hole velocities were measured with a 6 mm diameter microphone at nine positions per hole, and the acoustic pressures were converted to velocities with a propagating wavefront model. The surface measurements were compared to radiation measurements made with a 92 cm radius microphone array in an anechoic chamber. The surface measurements could be completed in a day, the radiativities in two hours. The resulting maps of operating deflection shapes, calibrated in m/s per N, allow a detailed examination of the vibrational behavior of each instrument, at frequencies up to and includin...

Non-axisymmetric response of piles in low-strain integrity testing

Low-strain testing of piles is routinely performed by striking the pile head with a small hand-held hammer, usually aiming for the pile centre, and measuring the vertical velocity response by means of a receiver placed also on the pile head. In practice, however, it is impossible for the operator to perfectly align the point of impact with the pile centre, as existing solutions for the interpretation of the velocity measurements assume. In the general case where the impact load is eccentric, the wave field is no longer axisymmetric with respect to the pile axis and waves resulting from the hammer impact can propagate along the vertical, radial and circumferential directions. This is taken into consideration in the analytical solution presented in this note, which provides the non-axisymmetric dynamic response of a pile to an impact load applied at an arbitrary position on the pile head. Arithmetic examples are used to depict the three-dimensional non-axisymmetric vibration characteristics of the soil–pile system, with emphasis on the effect of the eccentricity of the impact load on the optimal position of the receiver, the identification of which is essential for obtaining meaningful results from low-strain integrity tests.

Quick Assessment of the Anomalies in Concrete Structure Using Dispersive Characteristic of Surface wave

A waveform generated by a small impact hammer and recorded by single transducer is used to assess different kinds of anomalies in concrete. Using Short-Time Fourier Transform and the reassignment technique, the group slowness spectrogram can be calculated from the waveform. The surface wave response in the diagram of velocity vs. wavelength corresponding to the reassigned spectrogram is used for defect evaluation. Experiments were conduct on a concrete plate specimen containing multiple delaminated cracks, and a honeycomb. The group velocity profiles for test lines passing through different kinds of defects were obtained and compared. It was found the surface wave velocity begins to decrease with the increase of wavelength when the wavelength is about two times of the depth of the defect.

On the extraordinary strength of Prince Rupert's drops

Prince Rupert's drops (PRDs), also known as Batavian tears, have been in existence since the early 17th century. They are made of a silicate glass of a high thermal expansion coefficient and have the shape of a tadpole. Typically, the diameter of the head of a PRD is in the range of 5–15 mm and that of the tail is 0.5 to 3.0 mm. PRDs have exceptional strength properties: the head of a PRD can withstand impact with a small hammer, or compression between tungsten carbide platens to high loads of ∼15 000 N, but the tail can be broken with just finger pressure leading to catastrophic disintegration of the PRD. We show here that the high strength of a PRD comes from large surface compressive stresses in the range of 400–700 MPa, determined using techniques of integrated photoelasticity. The surface compressive stresses can suppress Hertzian cone cracking during impact with a small hammer or compression between platens. Finally, it is argued that when the compressive force on a PRD is very high, plasticity in the PRD occurs, which leads to its eventual destruction with increasing load.

Effects of Working Angle on Pneumatic Down-the-hole Hammer Drilling

The effects of the wor king angle on pneumatic down-the-hole (DTH) hammer drilling was investigated since these hammers were developed for vertical drilling and their performances in inclined positions need to be tested. The investigation begins by establishing a calculation model with which to simulate the percussive drilling of the hammer. The model consists of two parts. The first gives the kinetic energy of the piston at impact by simulating the thermodynamic cycle of the DTH hammer, and the second simulates the percussive drilling process according to the analyses of stress-wave propagation. In the meantime, a laboratory-scale test device was made for multi-angle hammer drilling tests. This device is based on a small pneumatic DTH hammer used in deep well drilling. By analyzing the force acting on the rock during impact at different angles, the percussive drilling process is carefully examined. Theoretical predictions and experimental results appear in fairly good agreement. The hammer’s working performance in inclined positions can be obtained directly using the proposed model. Furthermore, when detailed evaluation is required, the hammer can be tested using the method proposed in this paper.

The Marble-Hand Illusion

Our body is made of flesh and bones. We know it, and in our daily lives all the senses constantly provide converging information about this simple, factual truth. But is this always the case? Here we report a surprising bodily illusion demonstrating that humans rapidly update their assumptions about the material qualities of their body, based on their recent multisensory perceptual experience. To induce a misperception of the material properties of the hand, we repeatedly gently hit participants' hand with a small hammer, while progressively replacing the natural sound of the hammer against the skin with the sound of a hammer hitting a piece of marble. After five minutes, the hand started feeling stiffer, heavier, harder, less sensitive, unnatural, and showed enhanced Galvanic skin response (GSR) to threatening stimuli. Notably, such a change in skin conductivity positively correlated with changes in perceived hand stiffness. Conversely, when hammer hits and impact sounds were temporally uncorrelated, participants did not spontaneously report any changes in the perceived properties of the hand, nor did they show any modulation in GSR. In two further experiments, we ruled out that mere audio-tactile synchrony is the causal factor triggering the illusion, further demonstrating the key role of material information conveyed by impact sounds in modulating the perceived material properties of the hand. This novel bodily illusion, the ‘Marble-Hand Illusion', demonstrates that the perceived material of our body, surely the most stable attribute of our bodily self, can be quickly updated through multisensory integration.

Measurements of Piezoelectric Coefficient d33 of Lead Zirconate Titanate Thin Films Using a Mini Force Hammer

Lead zirconate titanate (PbZrxTi1-xO3, or PZT) is a piezoelectric material widely used as sensors and actuators. For microactuators, PZT often appears in the form of thin films to maintain proper aspect ratios. One major challenge encountered is accurate measurement of piezoelectric coefficients of PZT thin films. In this paper, we present a simple, low-cost, and effective method to measure piezoelectric coefficient d33 of PZT thin films through use of basic principles in mechanics of vibration. A small impact hammer with a tiny tip acts perpendicularly to the PZT thin-film surface to generate an impulsive force. In the meantime, a load cell at the hammer tip measures the impulsive force and a charge amplifier measures the responding charge of the PZT thin film. Then the piezoelectric coefficient d33 is obtained from the measured force and charge based on piezoelectricity and a finite element modeling. We also conduct a thorough parametric study to understand the sensitivity of this method on various parameters, such as substrate material, boundary conditions, specimen size, specimen thickness, thickness ratio, and PZT thin-film material. Two rounds of experiments are conducted to demonstrate the feasibility and accuracy of this new method. The first experiment is to measure d33 of a PZT disk resonator whose d33 is known. Experimental results show that d33 measured via this method is as accurate as that from the manufacturer's specifications within its tolerance. The second experiment is to measure d33 of PZT thin films deposited on silicon substrates. With the measured d33, we predict the displacement of PZT thin-film membrane microactuators. In the meantime, the actuator displacement is measured via a laser Doppler vibrometer. The predicted and measured displacements agree very well validating the accuracy of this new method.