In order to improve the detection sensitivity and stability of scanning laser ultrasound techniques, we propose a transmission time delay method, based on the time delay of transmitted longitudinal waves, for the evaluation of the size and position of an internal cavity. By studying the interacting process between the longitudinal wave and the internal cavity through theory and finite element method, the relationships among the time delay, cavity radius, and the detection distance were determined. The monotonicity of the relationship indicates that the time delay can be used to inverse the radius and the depth position of the internal cavity. The laser ultrasound experiments were performed on three aluminum samples with different internal cavities through the concentric transmission method. The C-scan results show that compared with using amplitude attenuation to detect the cavity, the time delay of transmitted waves can detect the internal cavities more stably and accurately. The experimental data are close to the theoretical and simulation results, and the inversion of cavity depth was achieved based on the measured parameters (the time delay, cavity radius, frequency, velocity). The results demonstrate that the transmission time delay method has a great application potential in the localization and quantification of the internal defects. [ABSTRACT FROM AUTHOR]
Copyright of International Journal of Thermophysics is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
