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Sensitive Damage Detection of Reinforced Concrete Bridge Slab by ``Time-Variant Deconvolution'' of SHF-Band Radar Signal
摘要： In this paper, we focus on ground-penetrating radar (GPR) for infrastructural health monitoring, especially for the monitoring of reinforced concrete (RC) bridge slab. Due to the demand of noncontact and high-speed monitoring technique which can handle vast amounts of aging infrastructures, GPR is a promising tool. However, because radar images consist of many reflected waves, they are usually difficult to interpret. Furthermore, the spatial resolution of system is not enough considering the thickness of target damages, cracks, and segregation are millimeter-to-centimeter order while the wavelength of ordinary GPR ultrahigh-frequency band is over 10 cm. To address these problems, for the purpose of sensitive damage detection, we propose a new algorithm based on deconvolution utilizing a super high-frequency (SHF) band system. First, a distribution of reflection coefficient is inversely estimated by 1-D bridge slab model. Because concrete is found to be a lossy medium at SHF band, we consider the attenuation of signal in deconvolution. The algorithm is called 'time-variant deconvolution' in this paper. After the validation by simulation, the effects of the algorithm and frequency band on damage detection accuracy are evaluated by a field experiment. Though the results show a 1-mm horizontal crack is not detected by measured waves, when it is filled with water, it is detected by time-variant deconvolution. Moreover, the 1-mm dried crack is detected only by time-variant deconvolution at SHF band, which greatly emphasizes the peaks of the reflection coefficient of the crack.
关键词： thin cracks and segregation detection,Ground-penetrating radar (GPR),infrastructural health monitoring,time-variant deconvolution
更新于2025-09-23 15:23:52
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Novel Three-Dimensional SiC/Melamine-Derived Carbon Foam-Reinforced SiO <sub/>2</sub> Aerogel Composite with Low Dielectric Loss and High Impedance Matching Ratio
摘要： Novel three-dimensional SiC/melamine-derived carbon foam composite filled by silica aerogel (SiC/MDCF?Aerogel) was first fabricated by the pyrolysis process of commercial melamine foam, chemical vapor deposition of ultrathin SiC films, and the sol?gel method of silica aerogel. The results indicated that the SiC/MDCF?Aerogel composite consisted of the SiC three-dimensional open-celled network structure and the pregnant silica aerogel in the pores. Tiny cracks on the interface of skeletons and clumps were induced during the aging process, which was drastically beneficial to the microwave-absorbing properties. A minimum reflection loss could be obtained as low as ?18.41 dB at the measured frequency of 16.92 GHz when the thickness of the absorber was 3.65 mm, and the reflection loss could drop below ?10 dB when the selected frequencies ranged from 15.80 to 17.52 GHz, along with the thickness ranging from 2.75 to 5.0 mm, which possessed a relatively better microwave absorption performance especially at a higher frequency. Furthermore, the absorption mechanism was also investigated in detail to discuss the influence of the dielectric loss and the impedance matching ratio on the microwave-absorbing performance of SiC/MDCF?Aerogel, which provided certain scientific directions for evaluating the absorbing materials.
关键词： Minimum reflection loss,Tiny cracks,Microwave-absorbing properties,Impedance matching ratio,Dielectric loss,SiC/MDCF?Aerogel
更新于2025-09-23 15:22:29
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Method for Processing and Analysis of the Images of a Network of Thermal Fatigue Cracks on the Surfaces of Rollers of Continuous Casting Machines
摘要： We propose an algorithm for the analysis of thermal fatigue cracks on the surfaces of rollers of continuous casting machines that does not require adaptation to images of various types and individual choice of parameters. For this purpose, the images are analyzed for a sufficiently large subset of the sets of values of the parameters. The result of this classification is regarded as a fuzzy set with a membership function of each element equal to the number of sets of parameters responsible for the detection of this element as a component of the frame of the damage grid.
关键词： image processing,thermal fatigue cracks,self-focusing,fuzzy sets,classification
更新于2025-09-23 15:21:21
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In situ x-ray diffraction analysis of 2D crack patterning in thin films
摘要： In this work, the effect of the loading path on the multicracking of Nickel thin films on Kapton substrate was studied thanks to an experimental set-up combining controlled biaxial deformation, x-ray diffraction and digital image correlation. Samples were biaxially stretched up to 10% strain following either a single equibiaxial path or a complex one consisting of loading successively along each of the axes of the cruciform specimen. While the first path leads to a mud-crack pattern (random), the second leads to a roman-bricks one (square). Moreover, the in situ x-ray diffraction experiments show that the stress field developed in the thin film during the multicracking is clearly dependent on the loading path. By combining the study of stresses and x-ray diffraction peaks linewidth, we evidenced mechanical domains related to initiation of cracks and their multiplication for each loading path. Moreover, stress evolution in the thin film during mud-crack pattern formation is significantly smoother than in the case of roman-bricks one as represented in the plane stress space.
关键词： Synchrotron,Mechanical properties,Flexible substrates,Cracks
更新于2025-09-23 15:21:21
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Femtosecond laser irradiation of titanium oxide thin films: accumulation effect under IR beam
摘要： This paper discusses the mechanisms of laser-induced periodic surface structures (LIPSS) formation using a high repetition rate femtosecond laser beam irradiation of magnetron-sputtered titanium oxide thin films (TiO1.8) grown onto SiO2/Si substrates. An Yb:YKW 500 fs linearly polarized laser emitting at a wavelength, λ, of 1030 nm, was used to irradiate the films (300 nm thickness) at a repetition rate of 100 kHz under both static and dynamic (scanning) conditions. Under static beam conditions, an incubation behavior related to materials in thin film form was established with a damage threshold of 72 mJ/cm2. Close to this fluence value and increasing the number of laser shots from 1 to 1000, micro-cracking occurred and propagated inside the beam waist diameter zone estimated close to 60 μm. In addition, using a higher fluence value of 280 mJ/cm2, i.e., well above the damage threshold, a melting occurred in an intermediate zone within the irradiated area, with a surprising ‘cure effect’ that contributes to the micro-cracks stabilization. Simultaneously, at the center of the Gaussian laser beam spot, the entire film ablation was observed. Furthermore, irradiation under dynamic mode with a scanning speed of 4 mm/s and a repetition rate of 100 kHz were achieved for the large-scale processing of the TiO1.8 films up to surface area of 25 × 25 mm2. For these irradiation conditions case that correspond to a fluence of 110 mJ/cm2 and a cumulative number of shots of 3000, 2D-LIPSS nano-cracks (200 nm length and λ/8 to λ/9 period) are obtained over the whole irradiated surface, a phenomenon that is mainly attributed to a thermo-mechanical ablation mechanism.
关键词： Femtosecond laser beam,Titanium oxide film,Micro/nano-cracks,High repetition rate,Incubation,LIPSS
更新于2025-09-23 15:21:01
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Rapid detection of building cracks based on image processing technology with double square artificial marks
摘要： In order to measure the crack width of dangerous buildings quickly and accurately, this article presents a new crack width measurement method, which is based on image processing technology, using double square artificial markers to identify building cracks and calculate crack width. It makes two 10 mm 3 10 mm black square artificial marks and places them near the sides of the crack. Then it uses a camera to collect crack images and transfer photos to a computer. The crack image is subjected to image graying, binarization, denoising, image segmentation, and pixel calibration based on the image processing technique. Finally, the actual length value of the unit pixel is calculated. Then it can calculate the actual width of the crack according to the number of pixels included in the test crack. The calculation results show that the accuracy of the proposed method is 98.56% compared with the measured data. The calculation method can accurately and effectively detect the crack width of dangerous buildings and improve work efficiency. At the same time, it can avoid long hours of work in dangerous operating environments.
关键词： building cracks,digital image processing,safety,MATLAB,double square artificial marks,crack width
更新于2025-09-23 15:21:01
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Measurement of shallow defects using noncontact broadband leaky Lamb wave produced by pulsed laser with ultrasound microphone
摘要： In this study, we propose a convenient noncontact laser ultrasonic system to detect small cracks and estimate the wall-thinning defects of thin plates. The system uses an ultrasound microphone to detect the energy leaked from the broadband Lamb-wave propagation. The broadband characteristics of this wave, produced by a pulsed laser, are used to measure the wavenumber. The cumulative standing-wave energy (CSWE) method that uses a traveling wave is implemented to verify the feasibility of the ultrasound microphone. The excitation energy of the pulsed laser was insufficient compared with that of the continuous-wave contact actuator. Therefore, a modified local wavenumber estimation (LWE) method is proposed, which reconstructs several LWE images at various frequencies. These images are averaged to calculate thicknesses of the plate and defects, by using the wavenumber–thickness relationship. The method has an error of 2.84% and 7.7% for the thickness of the plate and defect area, respectively.
关键词： cumulative standing-wave energy (CSWE),ultrasound microphone,local wavenumber estimation (LWE),wall-thinning defects,noncontact laser ultrasonic system,broadband Lamb-wave propagation,small cracks
更新于2025-09-23 15:19:57
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Fully noncontact measurement of inner cracks in thick specimen with fiber-phased-array laser ultrasonic technique
摘要： To realize a fully noncontact ultrasonic testing method for inner cracks inspection in thick metal specimen, a phased array laser ultrasonic testing system with using a compact optic fiber array bundle and a laser interferometer is developed in this study. The focusing and steering of the shear wave and longitudinal wave generated with seven fiber-phased-array laser sources in thermoelastic regime is investigated by a numerical simulation and validated by the experiment. A non-contact measurement of the inner-surface cracks by both the angle-beam testing method and time-of-flight diffraction method with the fiber-phased-array laser ultrasonic technique have been studied.
关键词： Fiber bundle,Laser ultrasonic testing,Phased array,Inner cracks
更新于2025-09-23 15:19:57
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Micro-cracks detection of solar cells surface via combining short-term and long-term deep features
摘要： The machine vision based methods for micro-cracks detection of solar cells surface have become one of the main research directions with its efficiency and convenience. The existed methods are roughly classified into two categories: current viewing information based methods, prior knowledge based methods, however, the former usually adopt hand-designed features with poor generality and lacks the guidance of prior knowledge, the latter are usually implemented through the machine learning, and the generalization ability is also limited since the large-scale annotation dataset is scarce. To resolve above problems, a novel micro-cracks detection method via combining short-term and long-term deep features is proposed in this paper. The short-term deep features which represent the current viewing information are learned from the input image itself through stacked denoising auto encoder (SDAE), the long-term deep features which represent the prior knowledge are learned from a large number of natural scene images that people often see through convolutional neural networks (CNNs). The subjective and objective evaluations demonstrate that: 1) the performance of combing the short-term and long-term deep features is better than any of them alone, 2) the performance of proposed method is superior to the shallow learning based methods, 3) the proposed method can effectively detect various kinds of micro-cracks.
关键词： solar cell,stacked denoising auto encoder,long-term,convolutional neural networks,short-term,micro-cracks detection
更新于2025-09-23 15:19:57
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Laser Powder Bed Fusion of high strength aluminum
摘要： Demands for high strength aluminum alloys processed by Laser Powder Bed Fusion (LPBF) are high and keep rising. However, expensive new alloy compositions or crack formation in existing alloys hinder its wide applicability. It is known from recent work that addition of grain refiners leads to a fine grain structure enabling crack-free, high strength aluminum LPBF parts. In this research, 1wt% of Zr was added to Al7050. Furthermore, an excess of Zn was provided in the powder material to compensate for Zn losses during LPBF and to maintain the Mg:Zn ratio required for formation of strong and coherent MgZn2 precipitates. After a solution and aging heat treatment, the newly developed alloy has an ultimate tensile strength of 500MPa and Vickers micro-hardness of 200Hv-0.5kg. Although the elongation at break of the resulting parts is limited, this research shows promising results for future alloy design of affordable high strength aluminum alloys to be processed by LPBF.
关键词： grain refinement,aluminum,Laser Powder Bed Fusion,cracks
更新于2025-09-23 15:19:57