Search Results (5)

The steel rail and wheel in the railway system offer a high precision and smooth-running surface. Nevertheless, the point of contact between the rail and wheel presents a critical area that can give rise to rail corrugation. This phenomenon can potentially elevate sound and vibration levels in the vicinity considerably, necessitating advanced monitoring and assessment measures. Recently, many efforts have been directed towards utilizing in-service trains for evaluating rail corrugation, and the evaluation has primarily relied on axle-box acceleration (ABA). However, the ABA measurements require a higher threshold for vibration detection. This study introduces a novel approach to rail corrugation detection by carriage floor acceleration (CFA), aimed at lowering the detection threshold. The method capitalizes on the acceleration data sensed on the carriage floor, which is induced by the sound pressure (e.g., sound-field excitation) generated at the wheel–rail contact point. An exploration of the correlation between these datasets is undertaken by simultaneously measuring both ABA and CFA. Moreover, a pivotal aspect of this research is the development of the eigenfrequency rail corrugation index (E-RCI), a mechanism that culminates energy around specific eigenfrequencies by CFA. Through this index, a focused analysis of rail corrugation patterns is facilitated. The study further delves into the stability, repeatability, and sensitivity of the E-RCI via varied measurement scenarios. Ultimately, the CFA-based rail corrugation identification is verified, establishing its practical applicability and offering a distinct approach to detecting and characterizing rail corrugation phenomena. This study has introduced an innovative methodology for rail corrugation detection using CFA, with the principal objective of lowering the detection threshold. This approach offers an efficient measurement technique for identifying rail corrugation areas, thereby potentially reducing maintenance costs and enhancing efficiency within the railway industry. Full article

Lead Zirconate Titanate (PZT) is used to make ultrasound transducers, sensors, and actuators due to its large piezoelectric coefficient. Several micro-defects develop in the PZT sensor due to delamination, corrosion, huge temperature fluctuation, etc., causing a decline in its performance. It is thus necessary to identify, locate, and quantify the defects. Non-Destructive Structural Health Monitoring (SHM) is the most optimal and economical evaluation method. Traditional ultrasound SHM techniques have a huge impedance mismatch between air and solid material, and most of the popular signal processing methods define time series signals in only one domain, which provides sub-optimal results for non-stationary signals. Thus, to improve the accuracy of detection, the point contact excitation and detection method is implemented to determine the interaction of ultrasonic waves with micro-scale defects in the PZT. The signal generated from this method being non-stationary in nature, it requires signal processing with changeable resolutions at different times and frequencies. The Haar Discrete Wavelet Transformation (DWT) is applied to the time series data obtained from the coulomb coupling setup. Using the above process, defects up to 100 μm in diameter could be successfully distinguished. Full article

This work determined the attenuation coefficients of Lamb waves of ten engineering materials and compared the results with calculated Lamb-wave attenuation coefficients, α–S and α–A. The Disperse program and a parametric method based on Disperse results were used for calculations. Bulk-wave attenuation coefficients, α_L and α_T, were required as input parameters to the Disperse calculations. The calculated α–S and α–A values were found to be dominated by the α_T contribution. Often α–A_o coincided with α_T. The values of α_L and α_T were previously obtained or newly measured. Attenuation measurement relied on Lamb-wave generation by pulsed excitation of ultrasonic transducers and on surface-displacement detection with point contact receivers. The frequency used ranged from 10 kHz to 1 MHz. A total of 14 sheet and plate samples were evaluated. Sample materials ranged from steel, Al, and silicate glass with low attenuation to polymers and a fiber composite with much higher attenuation. Experimentally obtained Lamb-wave attenuation coefficients, α–S and α–A, for symmetric and asymmetric modes, were mostly for the zeroth mode. Plots of α–S_o and α–A_o values against frequency were found to coincide reasonably well to theoretically calculated curves. This study confirmed that the Disperse program predicts Lamb-wave attenuation coefficients for elastically isotropic materials within the limitation of the contact ultrasonic techniques used. Further refinements in experimental methods are needed, as large deviations often occurred, especially at low and high frequencies. Methods of refinement are suggested. Displacement measurements were quantified using Rayleigh wave calibration. For signals below 300 kHz, 1-mV receiver output corresponded to 1-pm displacement. Peak displacements after 200-mm propagation were found to range from 10 pm to 1.5 nm. With the use of signal averaging, the point-contact sensor was capable of detecting 1-pm displacement with 40 dB signal-to-noise ratio and had equivalent noise of 4.3 fm/√Hz. Approximate expressions for α–S_o and α–A_o were obtained, and an empirical correlation was found between bulk-wave attenuation coefficients, i.e., α_T = 2.79 α_L, for over 150 materials. Full article

Electroluminescence (EL) is a powerful tool for the qualitative mapping of the electronic properties of solar modules, where electronic and electrical defects are easily detected. However, a direct quantitative prediction of electrical module performance purely based on electroluminescence images has yet to be accomplished. Our novel approach, called “EL power prediction of modules” (ELMO) as presented here, used just two electroluminescence images to predict the electrical loss of mechanically damaged modules when compared to their original (data sheet) power. First, using this method, two EL images taken at different excitation currents were converted into locally resolved (relative) series resistance images. From the known, total applied voltage to the module, we were then able to calculate absolute series resistance values and the real distribution of voltages and currents. Then, we reconstructed the complete current/voltage curve of the damaged module. We experimentally validated and confirmed the simulation model via the characterization of a commercially available photovoltaic module containing 60 multicrystalline silicon cells, which were mechanically damaged by hail. Deviation between the directly measured and predicted current/voltage curve was less than 4.3% at the maximum power point. For multiple modules of the same type, the level of error dropped below 1% by calibrating the simulation. We approximated the ideality factor from a module with a known current/voltage curve and then expand the application to modules of the same type. In addition to yielding series resistance mapping, our new ELMO method was also capable of yielding parallel resistance mapping. We analyzed the electrical properties of a commercially available module, containing 72 monocrystalline high-efficiency back contact solar cells, which suffered from potential induced degradation. For this module, we predicted electrical performance with an accuracy of better than 1% at the maximum power point. Full article

To date in most cases of high-grade nerve injuries only partial recovery is achieved and the prognosis is still poor for some types of lesions. Neurophysiological methods are implemented to improve the outcome by assessing the condition of nerve fibres at any location and at any point of time during the course of surgery. Monitoring is utilised to prevent inadvertent injury during surgical procedures. Free-running EMG signals are recorded from muscles targeted by a nerve at risk. Motor unit activity is initiated when dissecting instruments approach and contact the nerve. Bursts and neurotonic discharges arise and increase with tension or pressure exerted on the nerve. Acoustic feedback warns of imminent damage. Evoked muscle and cerebral potentials are applied to reveal impairment of the nerve excitability and conductivity by mechanical and metabolic stress. Under normal conditions nerve action potential (NAP) recording from the exposed nerve reflects the integrity of the nerve by high amplitude, steep rise and normal temporal dispersion. Under pathological conditions the reduced density of nerve fibres, thickening of nerve sheaths, endoneurial cell proliferation and many other influences enhance the amplitude reduction of the NAP and may cause overestimation of nerve malfunction. However, this enhancement facilitates the detection of the location and the extension of the lesion. In nerve tumour surgery NAP recording identifies affected and unaffected nerve fascicles and the border of healthy tissue. In traumatology following closed nerve injuries early revision and evaluation with the aid of NAP recording has proved to be the best possible procedure. When the nerve is found in continuity, the appearance of the nerve does not reliably reflect the grade of the lesion and the prognosis. Resection of low-grade injuries, capable of spontaneous regeneration downgrades the outcome. If a highgrade lesion without potential of regeneration is not resected and repaired, recovery is not possible. To avoid inadequate measures, nerve surgery is frequently delayed awaiting muscle reinnervation. However, this loss of time has the most adverse impact on final outcome when repair is necessary. Neurography detects the presence or absence of significant nerve regeneration in the early months following the injury. Where the lesion is found in continuity after 3–4 months and NAPs are recorded across the lesion, neurolysis is done in order to promote nerve regeneration.Where NAPs are not recordable, resection and repair are required. In the same way NAP recording is used to judge single fascicles. Split nerve repair is done if some fascicles are conductive and others are not. When nerve repair is indicated, the proximal stump has to be sectioned back “to healthy tissue”. However, as intraoperative nerve evaluation by gross inspection and magnification does not reliably reflect the availability and viability of nerve fibres,NAP recording is recommended as an additional criterion for choosing an appropriate proximal coaptation site for reconstruction. Intraoperative nerve function assessment is essential for brachial plexus surgery. As nerve repair is useless in the presence of preganglionic lesion, SEPs are applied to assess the integrity of the dorsal root. NAPs with high amplitude in the absence of nerve function are also useful tools to identify preganglionic lesions. With the aid of intraoperative SEP and NAP recording in plexus surgery surgical measures are selected according to the integrity of the roots, the quality of nerve parenchyma and the potential of regeneration across lesions in continuity. Intraoperative recording from the exposed nerve improves the understanding of pathophysiology of focal neuropathies as exemplified by studies on the ulnar nerve entrapment at the elbow. Full article