The Spec-Radiation Method as a Fast Alternative to the Re-Radiation Method for the Detection of Flaws in Wooden Particleboards

For real-time evaluation of non-destructive air-coupled ultrasonic testing of wood-based materials, efficient and reliable calculation methods from ultrasonic holography are essential. Presented here is the spec-radiation method as a fast alternative to the re-radiation method. The spec-radiation method offers a more accurate and up to 88% faster evaluation than the re-radiation method for the determination of flaws in particleboards. Flaws of sub-wavelength sizes can be identified and their shape and location can be determined with this method. The spec-radiation method produces a better reproduction of the sound field than the re-radiation method, especially in the area of the measuring plane

The Spec-Radiation Method for Layered Fluid Media

The real-time evaluation for non-destructive air-coupled ultrasonic testing of panel materials is a big task for several industries. To make these tests more and more accurate, efficient and reliable calculation methods from ultrasonic holography are essential. In the past, we presented the spec-radiation method as a fast and accurate method for such tasks. The spec-radiation method calculates the sound field utilizing data from a measurement plane at another parallel or tilted plane, especially the sound field at the surface of a panel. This can be used to detect flaws. There is a limitation of the current method: using the data on the panel surface limits the accuracy of the detected flaws. A big step forward could be expected if the sound field in the material were known. As a first step, we developed the spec-radiation method forward to consider multiple material layers. For now, we made the major assumption that all layers have fluid-like properties. Hence, transversal waves were neglected. This extension of the spec-radiation method was validated utilizing an experiment. We present that flaws in the panel material can be detected with higher accuracy at a similar speed compared to our former approach

Flaw detection on a tilted particleboard by use of the spec-radiation method

Herein, we present a novel approach to the spec-radiation method (a method of acoustical holography) for determining the sound distribution on a tilted particleboard by calculating a single plane and rotation in the frequency domain. The tilted particleboard allows testing without standing waves between the transmitter and the particleboard. This eliminates the need to evaluate several parallel planes and to search for values belonging to the tilted particleboard. The numerical requirements can be optimally exploited through a combination with a flaw detectability enhancement method. The results are supported by experiments on a wooden particleboard with flaw imitations. Finally, we showed, through a comparison with the usual procedure of identifying a flaw (calculating many parallel planes and then selecting the data belonging to the tilted plane), that the calculation of the tilted plane is up to 98.5% faster and improves the detectability of flaws in a tilted particleboard

Experimentelle und modellbasierte Untersuchung von Stehwellenantrieben

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Self-sensing cavitation detection capability of horn geometries for high temperature application

Cavitation is utilized in a wide range of applications. As examples ultrasonic cleaning baths and emulsification in sonochemistry may be mentioned. For a high temperature ultrasonic assisted casting process, the authors’ aim is to detect cavitation in the ongoing process using cavitation noise spectra without additional sensors like hydrophones, which disturb the sound field. The authors’ aim is to detect cavitation from the ultrasonic transducers’ current signal. Two different horn geometries are tested for their cavitation detection capability. To investigate the frequency components in the transducers’ current signal without the influence of the horns’ individual transfer functions, the measured data are processed to obtain the uninfluenced signals. Different frequency components are found in the measurements, which can be used as indicators for cavitation

Visualization of dynamic stress conditions in elastic solids utilizing high frequency stroboscopic LED arrays

Ultrasonic mechanical vibrations in solids are widely used in non-destructive testing, and high-power applications such as ultrasonic welding or soldering. The visualization of ultrasonic wave propagation in transparent solids is helpful for understanding the ultrasonic behaviours. The classical method of photoelasticity allows the visualization of the static stress distribution in birefringent materials. Utilizing recent high-power LEDs in the photoelasticity allows to capture dynamic stresses by high frequency stroboscopic light. High frequency stationary and transient oscillation processes in elastic solids can be visualized with this method. The designed LED array in this paper has a dimension of 210 mm 300 mm, and every LED has distance of 38mm to each other, and the light intensity has a homogeneity value. The temporal and spatial resolution of stress-optic systems depends mainly on the dynamic properties of the lighting technology used. The high speed synchronization of the stroboscopic light sources results in a high temporal resolution of the photoelasticity analyses. This enables the photoelastic investigation of highly dynamic load conditions, such as longitudinal waves and transverse waves

Investigation of Impact Loads Caused by Ultrasonic Cavitation Bubbles in Small Gaps

Ultrasonic cavitation shows a great potential in various industrial applications such as sonochemistry, food processing, ultrasonic cleaning, and surface treatments. These applications have the advantages of high temperatures or high pressure due to the collapse of cavitation bubbles. In surface treatments, the collapse of bubbles occurs near workpiece surfaces and creates micro-jets which lead to high impact forces. As one of these surface treatment processes, ultrasonic cavitation peening requires a small gap between the vibration source and the treated surface to obtain the maximum impact force. Due to these small gaps, the growth and collapse of cavitation bubbles are affected, which result in the changes of impact forces. Therefore, the investigation of the impact loads caused by ultrasonic cavitation bubbles in small gaps is the focus of this contribution. A theoretical model taking into consideration bubble interactions is utilized to estimate the optimal standoff distance at which the largest impact forces occur. Then, experimental investigations are carried out. A piezoelectric sensor with a titanium alloy cover is used to record the number of impacts and their amplitudes. The recorded signals are then processed in time and frequency domains. The experimental results show that large impact loads are generated when the gap width is in the range of 0.5-0.8 mm. It is also found that the maximum working efficiency occurs in this range

Investigation and enhancement of the detectability of flaws with a coarse measuring grid and air coupled ultrasound for NDT of panel materials using the re-radiation method

Non-destructive ultrasonic testing is utilized widely by industries for quality assurance. For sensitive materials or surfaces, non-contact, non-destructive testing methods are in demand. The air-coupled ultrasound (ACU) is one possible solution. This can be used to investigate large, panel-like objects for delaminations and other flaws. For a high detectability, fine measurement grids are required (typically <λ is used), which results in extremely long data acquisition times that are only practicable for laboratory applications. This paper aimed at reducing the required measurement grid points for obtaining high detectability evaluations. The novel method presented in this paper allows a measurement grid that is much coarser than the resulting grid. The method combines a software refinement of the measured data with the Rayleigh-Sommerfeld diffraction integral for the calculation of the pressure distribution on the object's surface. This result allows the precise prediction of delaminations and flaws in the tested object. The presented method shows a decrease in the total investigation time by up to 98%

Investigations on the mechanism of microweld changes during ultrasonic wire bonding by molecular dynamics simulation

Despite the wide and long-term applications of ultrasonic (US) wire bonding and other US metal joining technologies, the mechanism of microweld changes during the bonding process, including formation, deformation and breakage, is rarely known as it is very difficult to be investigated by experiments. In this work, this mechanism under different surface topographies and displacement patterns is studied by molecular dynamics simulation. It is found that microwelds can be formed or broken instantly. Due to the relative motion between the local wire part and the local substrate part, microwelds can be largely deformed or even broken. The impacts of material, surface topography, approaching distance and vibration amplitude on the microweld changes are investigated via the quantification of the shear stress and the equivalent bonded area. It is shown that these four factors significantly influence the final connection and the interface structure. The analysis of the scale influence on the microweld changes shows that the simulation results at a small-scale are able to represent those at a large-scale which is close to the range of the commonly used surface roughness. This deeper understanding on the microweld changes leads to a better control strategy and an enhancement of the bonding process