Damage Monitoring For The Crane Structure Of Concrete Pump Trucks Based On Ultrasonic Guided Waves

The safety and reliability of the cantilever crane which is the main bearing structure of a concrete pump truck has been receiving increasing attention. For this specific requirement, structural health monitoring(SHM) using guided waves is considered as one of the most promising technologies thanks to its potentials of large monitoring range and high sensitivity to small defects. In order to apply this technology to the special structure of the crane of the concrete pump truck, this thesis mainly focuses on the corresponding damage monitoring methods based on Lamb waves.Firstly, basic theories of Lamb waves in plates are introduced. The disperse property and multi-mode property of Lamb waves are stated in detail. In addition, the monitoring system based on Lamb waves is established and the corresponding working manners of the system are designed to realize the system automation using the Lab VIEW software.Secondly, this paper describes the rules for deciding the excitation frequency of Lamb waves, which is crucial to the damage monitoring approaches. The ABAQUS software is adopted to analyze interaction of damage with the propagating Lamb waves. Specifically, finite element modeling methods are presented and some series of cases are analyzed to reveal the relationship between damage severity and the amplitude of damage-induced scattering Lamb waves.Thirdly, this paper uses a time-frequency method which names complex Morlet wavelet transform to extract characteristic parameters from response Lamb wave signals for further damage monitoring methods. After that, the delay-and-sum method is clarified for damage localization. Combined with the proposed adaptive valid data extraction method, it is used to locate damage on the steel plate in the laboratory environment. Once obtaining the precise location of damage, a damage severity evaluation method is proposed based on support vector machine(SVM).At last, damage monitoring methods for the crane structure of the concrete pump truck are designed. On the basis of the self-defined damage index, a multi-damage diagnosis method is proposed to detect multi-damage in multiple subareas. Adaptive damage localization process is then applied to the subareas where damage exists. In addition, the influence of the deviation of the system-setting velocity on the localization accuracy is evaluated. To improve the intuition of the damage image, a boundary processing method is designed. Furthermore, this paper proposes a baseline-free damage localization method based on active impact excitations. The method realizes accurate damage localization according to the symmetry of the monitoring area.