PARAMETERS CHOICE IN ULTRASONIC GUIDED WAVES TESTING OF COMPOSITE PIPES BASED ON TOTAL ENERGY DENSITY

摘要

The paper describes an investigation of the longitudinal guided waves propagation characteristics in composite pipes. The dispersion characteristics were computed on the assumption that the frequency is real number and wavenumber is complex number. The Total Energy Density (TED) amplitude distributions of guided waves and its maximum were obtained and analyzed. Finally, the optimal location, optimal mode and its frequency-thickness products of testing are chose by TED. The results showed that the values of TED of guided waves is larger at inside layer than those at outside layer for two layers composite pipe. TED of the odd order modes has larger values than TED of the even modes. With the change of frequency-thickness products, there have several maximal values and minimal values of TED at inner and outer wall of inside layer. The positions of Maximal TED (MTED) of L(0,1) in around 0.1MHz mm and 0.55 MHz mm, and L(0,2) mode is in around 0.45MHz mm and 1.28 MHz mm, while the value of L(0,3) mode at is about 0.67 MHz mm and L(0,5) mode is at about 1.4MHz mm. Therefore, from energy's point of view, guided waves should be sensitive to the defect in the wall of pipes at the position of larger TED. On the other hand, at the ranges of frequency-thickness products of larger group velocity of each mode, this mode has feeble dispersion, while the other modes have smaller group velocity and stronger dispersion. And in that range, the mode has a larger TED at the wall of pipes. Therefore, at the range of frequency-thickness products of larger group velocity of each mode, using this mode to testing composite pipes should more ideality, the results agree with each other.