Research On Nonlinear Ultrasonic Modulation Detection Technology For Nonmetallic Pipeline Structure Damage

With the development of the application of nonmetallic pipes in recent years, nonmetallic pipe structure as petrochemical, urban agriculture, production or distribution network. Concerned the relationship to the safety of personnel and equipment, the researchs on nonmetallic pipe structural damage effective detection methods are constantly emerging, which has also been frontier problem in the filed of structural health monitorin. While nonmetallic pipes mainly in polymer materials are difficult to detecte accurately and effectively, this thesis for research on nonlinear ultrasonic modulation detection technology for nonmetallic pipeline structure damageas its title. Combined with nonlinear ultrasonic testing technology characteristics, active acoustic emission are studied on nonmetallic pipes, which provides a novel method for the detection of nonmetallic pipes structural damage based on nonlinear ultrasonic damage detection. Also, this thesis provides a theoretical basis for the nonmetal pipeline monitoring technique to assess the damage and damage location, which has important academic value and engineering significance to the safe use of nonmetallic pipelines. The research is supported by Guangdong National Natural Science Fund(2014A030313248) and Fund of Administration of Quality and Technology Supervision of Guangdong Province in 2016.(1)Process of nonmetallic pipe damage was analyzed from the theory as well as the nonlinear ultrasonic damage detection mechanism, which is the basis of nonlinear dynamic equation of damage detection. According to the deficiency of nonlinear detection techniques and the need of the actual damage, a novel nonmetallic pipe structure damage with nonlinear ultrasonic detecting technology was brought up.(2)According to the nonmetallic pipeline structure, the active acoustic emission was applied to the damage detection to realize the damage assessment. Nonlinear ultrasonic signal excitation from the same end was proposed, and the wavelet energy of modulation sideband was obtained by using wavelet packet decomposition method. The relation between nonmetallic pipe damage size and sideband components that is is monotonic was established. A nonlinear signal processing method was used to reduce the high attenuation and weakening effect of ultrasonic guided wave propagating in nonmetallic pipes.(3) With ultrasonic guided wave propagation characteristics and frequency response of nonmetallic pipe, nonlinear mixing delay excitation signal was made to establish location equation of a nonmetallic pipe with nonlinear ultrasonic detecting method. HHT was used to extract the instantaneous characters of the localization of multi regional damages, whicn achieves mulit area damage location.(4) The nonlinear pipeline damage assessment and damage location were achieved in algorithm. Nonmetallic pipeline damage detection experiment was carried out, the mixing ultrasonic excitation signal was analyzed in frequency domain. Using nonlinear ultrasonic damage assessment to calculate the size of damage and the nonlinear ultrasonic location with time delay calculate damage location. The results show that it can obtain the damage size and location effectively and accurately.(5) At the end of the paper, a model of nonmetallic pipe covered by concret with different thickness. The nonlinear ultrasonic location with time delay was applied to detect the damage. The results show that the technique can effectively detect the damage under the condition of the concrete and can achieve the detection of damage on the nonmetallic across a brick.