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In order to address the problem of poor imaging detection of internal defects caused by the multi-layer curved surface structure and strongly attenuating material of composite insulators, the total focusing method (TFM) with two-layer curved surface correction was investigated, Virtual source (VS) technology was introduced to improve the transmitted energy of the single-element transmission, combined with the delay multiply and sum (DMAS) algorithm to improve the signal-to-noise ratio (SNR) and ultrasonic imaging detection of defects of different sizes of side-drilled holes (SDHs) in the sheath layer and core rod layer. An examination ofthe delamination defects at the core rod layer of the composite insulators was also carried out. The results show that the double-layer surface correction method is able to calibrate the propagation time of the ultrasonic wave to accurately localise the defects. Moreover, the VS technique is able to effectively detect SDI-15 and delamination defects in the core rod layer that cannot be detected using the conventional TFM. After incorporating the DMAS technique, the average SNRs of the TFM and virtual source total focusing method (VSTFM) are improved by 12.75 dB and 13.77 dB, respectively. This shows that the DMAStechnique can significantly improve the SNR of detection. [ABSTRACT FROM AUTHOR]

A binocular vision measurement system provides a simple method for obtaining three-dimensional vibration data from moving objects, which is suitable for vibration monitoring of large structures such as bridges. Aiming to address the problem that the feature selection process for binocular visual inspection affects the measurement accuracy, chequerboard feature points are selected in this paper for carrying out a visual displacement measurement method. Firstly, pixel coordinate matching of the inner corner points in the chequerboard is completed and then a binocular vision measurement system is established. The measurement results are compared with using circular feature points. Secondly, the binocular vision measurement model is applied to the vibration measurement of a cantilever beam. Using comparisons with a three-axis acceleration sensor, the effectiveness and accuracy of this method are evaluated. Finally, the method is applied to measure the vibration of the cantilever beam under different load conditions and its vibration characteristics are analysed. The results show that the accuracy of the binocular vision measurement method based on pixel coordinate matching of the inner corner points in the chequerboard is higher than that using circular feature points. From comparisons with the acceleration sensor, the measurement error of this method is found to be small. In addition, the method can effectively analyse the vibration performance of a cantilever beam under different load conditions. Therefore, this measurement method is effective and provides a theoretical basis for the identification of vibration characteristics in large engineering structures. [ABSTRACT FROM AUTHOR]

The content of the long-period stacking ordered (LPSO) structure strengthening phase has an important influence on the tensile strength, compressive strength, ductility and other mechanical properties of magnesium (Mg) alloys. Therefore, effective detection of the volume fraction of the LPSO phase plays an important role in understanding the properties of the alloy. Focused on the problem that the accuracy of the non-destructive testing method for the LPSO phase precipitates with micron or nanometer scale is not sufficient, this paper studies the non-linear ultrasonic testing of the Mg alloy LPSO phase volume fraction. Based on the non-linear ultrasonic testing theory, the non-linear ultrasonic simulation of the simulation models with different LPSO phase contents was carried out using finite element simulation. The relationship between the volume fraction of the LPSO phase and the non-linear coefficient of ultrasonic simulation was studied and a non-linear ultrasonic testing system was established to test the Mg alloy specimens with different LPSO phase volume fractions. The results show that the non-linear ultrasonic testing method is sensitive to changes in the LPSO phase volume fraction. Thus, this method is an effective way to detect the LPSO phase volume fraction. [ABSTRACT FROM AUTHOR]

The threshold for binarisation of an ultrasonic C-scan image has a significant effect on flaw sizing. The 6 dB drop method shows poor performance when extracting flaws from an ultrasonic image. A novel method is presented to improve the accuracy of flaw sizing, whereby the flaws are separated from the background using digital image processing techniques including the Otsu method, bilateral filtering and dilation. The optimised thresholds for each flaw are calculated using the enumeration method to binarise the original image and then the flaw size is predicted using the 6 dB drop method. The dynamic threshold model for flaw sizing is developed on the basis of the generalised regression neural network theory, where the flaw peak value, the depth of flaw echo and the pre-judgement size of the flaw are all taken into consideration. Finally, ultrasonic C-scan experiments are conducted on an AZ80 magnesium alloy shell with natural flaws. Compared with the traditional 6 dB drop method, the experimental results show that C-scan imaging using the dynamic threshold method can reduce the average relative error of flaw sizing from 40.6% to 7.4%. [ABSTRACT FROM AUTHOR]