| Welding, as an important connection structure in special equipment and deep sea platform, always works in high pressure, strong corrosion, heavy load condition, which will affects the efficiency and safety of industrial production. However, traditional nondestructive testing(NDT) methods have the disadvantage of low detection efficiency, and can’t meet the request of large and irregular weld structure.Nowadays, ultrasonic guided waves are widely applied to detecting the defects in one-dimensional structures due to its advantages of rapid and long range detection. Welding structure can be taken as a special waveguide, and when its structure and material are changed, the propagation characteristics of the guided-wave will also be changed. To search the low-leaky, low-dispersion mode and frequency in welds with different materials and structures, research is important to the modes’ displacement field, dispersion characteristics and attenuation characteristics. In this article, series of studies have been conducted, including the basic theory, numerical modeling, testing system, group velocity and attenuation detection. The main researches are listed as follows:1) According to the Snell’s law, the formation mechanism of feature-guided modes has been discussed. After that, the semi-analytical finite element models of welding feature-guided wave has been established. Through the analyzing of displacement field of modes, two fundamental modes in welds, which named SHw0 and Sw0 mode, have been discussed.2) The semi-analytical finite element models of weld with different parameters are established, and the propagation characteristics of two modes at the frequency between 50 KHz and 400 KHz has been discussed. The SHw0 mode is found the characteristic of non-leaky, low-dispersion and properties remain steady. The phase velocity and attenuation characteristics of SW0 modes are greatly influenced by the structure.3) The experiment system of welding feature-guided wave has been established. In the experiments, propagation, distribution, phase velocity and attenuation characteristics of the SHW0 and SW0 mode has been discussed and proved to be match well with the simulated results. The SHW0 and SW0 mode are been excited to detect three fabricated types of defects, results show that SHW0 mode is suitable for detecting defects parallel to weld and SW0 mode is suitable for detecting defects vertical to weld.According to the experimental and analysis results, SHW0 and SW0 mode have different propagation characteristics in welds with different materials and structures, and its energy is propagated along the weld, which provides foundation for the practical application of the welding feature guided wave. |
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