Results 1 - 10 of 114
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[en] The article Evaluation of surface cracks of bending concrete using a fully non-contact air-coupled nonlinear ultrasonic technique, written by Jun Chen, Chenglong Yang and Quanquan Guo, was originally published online without open access.
[en] Low frequency piezocomposite transducers have been used in combination with pulse compression methods to penetrate into concrete-type materials. Ultrasonic Chirp signal with a frequency range 100 - 200 kHz and of 10 ms time duration was used to excite a pair of 54 mm diameter piezocomposite transducers in patch-catch mode. The centre frequency of the signal was 170 kHz. The result shows that some good signals with acceptable frequency were obtained. There was a problem with variability due to the high degree of scattering because the result had changed even with small changes in transducer position. Thus, an additional signal processing method was introduced, whereby the total energy reaching the receiver was calculated as a function of time from the cross-correlation outputs. (author)
[en] This PhD work focuses on the early detection by ultrasonic non - destructive testing (NDT) of two concrete swelling pathologies, the Delayed Ettringite Formation (DEF) and the Alkali Silica Reaction (ASR). These lead to damage the concrete first by micro-cracking, then by cracking. The early detection of these pathologies in the laboratory and then on site is a major safety issue, particularly in the case of strategic structures such as nuclear ones (containment buildings, radioactive waste storage galleries, etc.). The literature review revealed two limitations. The first one is the lack of data on the sensitivity of nonlinear acoustics and acoustic emission to DEF, since the detection capability in linear acoustics is low for kinetics of swelling typical of affected structures. The second one requires the development of NDT techniques able to detect and locate pathologies at the centre of thick concrete blocks. Thus, the first part of this work is dedicated to monitoring the accelerated development of DEF in small laboratory samples (7 x 7 x 28 cm3) by the following NDTs: Resonant Ultrasonic Spectroscopy (RUS), Nonlinear Resonant Ultrasonic Spectroscopy (NRUS) and Acoustic Emission (EA). The results of these tests are interpreted through microscopy analyses. To address the second issue, a large block (40 x 40 x 70 cm3) containing a sandstone ball simulating a pathological zone due to its highly non-linear properties was poured. This block enabled the development of a non-classical nonlinear acoustics method based on the interaction between a propagative pump wave and a probe wave. The method developed in this work allowed the sandstone ball to be detected and located with a high contrast. These results represent an encouraging advance in the detection of swelling pathologies in the absence of generalized and visible degradation in large concrete elements. Finally, an approach aiming at converting the measured values in quantitative non-linear acoustics is proposed. For this purpose, a numerical approach calibrated from experimental measurements and taking into account the viscoelasticity of the concrete allows determining the amplitude of deformation on the trajectory of the probe wave. It is therefore possible to establish a link between the NDT measurement and the progress of the pathology. The results of this PhD work pave the way for an on - site transfer of the proposed method. (author)
[en] Full-text: In the industry, phased array ultrasonic testing (PAUT) has been applied widely and accepted by owners about standards that has been published. PAUT probes have multi elements consisting of 8, 16, 32 64, 128 or 256 elements which can be individually excited and recorded. PAUT systems applies focal laws which are time delayed triggers of individual elements which in turn will determine the shape of beam produced. The operators can select the depth of electronic focusing to suit the material under inspection. However, the certain depth of electronic focusing can cause defects which lies outside the depth of focusing to be enlarged or undetected entirely. This paper studies the effects of electronic focusing on the detectability and sizing of defects in carbon steel. Olympus Omniscan MX2 was used together with 5MHz 64 elements probe. The reflectors used is Side Drilled Hole with 1.5 mm diameter. Simulation was also performed using CIVA software. (author)
[en] Methods based on propagation of stress wave phenomena indicate particularly useful in diagnosis of non-metallic materials. The aim of this research is to demonstrate that ultrasonic measurement can produce satisfactory results in predicting certain mechanical properties of standing Aquilaria malaccensis tree. The mechanical information is very important to diagnose the condition inside the trunk. The experiment has been conducted on agarwood samples using a pulse compression ultrasonic system. The apparatus equipped with exponential horn 54 kHz piezoelectric normal probe. Through transmission method of longitudinal ultrasonic wave has been used throughout this experiment to measure velocity of ultrasonic signal through the sample. The result showed that the ultrasonic technique can be used in diagnosing of wood-based samples. (author)