| Quay container crane is the main equipment of port container stevedoring.The crane is prone to crack due to the comprehensive action of lifting load,stress concentration,environment and other factors in the process of operation.If crack can not be detected in time,it will accelerate expansion under cyclic loads and result in sudden fracture,leading to catastrophic consequences.There are many kinds of cracks in the metal structure of quay container crane,such as surface cracks and through-thickness cracks.The cracks not only exist in large metal plate,but also in stress concentration areas such as machining holes and welds.Therefore,it has important academic significance and engineering application prospect to carry out research on monitoring technology and evaluation method of cracks in metal plate.In order to meet the industrial demand of safe operation about metal plates,the ultrasonic Lamb wave and SH wave propagation characteristics of cracks in metal plates was studied.On this basis,the monitoring and quantitative evaluation method of through-thickness cracks in thin metal plates based on Lamb wave was proposed,and the research on the ultrasonic SH wave and Lamb wave monitoring technology of cracks in thick metal plates of quay container crane was carried out.The main research contents include:(1)The simulation research of parameter setting and electric excitation loading of piezoelectric ceramic sensor,which can excite ultrasonic Lamb wave was carried out.And the simplified excitation loading mode was obtained.The propagation model of ultrasonic Lamb wave and SH wave for crack in metal plate was established.The influence of crack parameters(length,depth,etc.)on the propagation characteristics of ultrasonic guided wave was studied.The results showed that Lamb wave signals scattered by crack have the phenomenon of mutual conversion between symmetric mode and asymmetric mode,and the amplitude of mode conversion signal is closely related to the crack parameters.There is no mode conversion for SH wave signal scattered by crack.And with the change of crack parameters,the amplitude change of reflected signal is more significant than that of transmitted signal.(2)Combined with the method of three-dimensional finite element simulation and experiment,the Lamb wave characterization method of through-thickness crack parameters by circular sensor network was studied in depth.The Lamb wave characterization method of different crack length,different angle and crack tip was analyzed.The results showed that the amplitude and phase of transmission signal are approximately linearly related to the length of crack,and are piecewise linear correlation related to the angle(Angle between sensing path and crack length direction),and does not change significantly when passing through the crack tip.(3)The monitoring and quantitative evaluation method of through-thickness crack in thin metal plate was studied.Based on the propagation characteristics and characterization methods of ultrasonic Lamb waves with crack in metal plates,a damage index(DI)solution method which can effectively reflect the characteristics of through-thickness cracks was proposed.And this method is superior to the traditional correlation analysis method.Based on the characteristics of DI in different angles and reconstruction algorithm for the probabilistic inspection of damage,the crack direction recognition method was proposed.A database of DI for different crack sizes was established,and a probability assessment method of crack size based on DI was proposed.Experimental results showed that the method can reconstruct the crack image,and evaluation error is less than 15%.(4)The failure mode of metal structure in quay container cranes was analyzed,and it was revealed that fatigue fracture is the main failure mode of the front drawbar.Based on the magnetostrictive ultrasonic SH wave technology,research on the monitoring technology of stress release hole edge crack and weld crack in the front drawbar was carried out.And the change rule of monitoring signals with the crack evolution was obtained in time domain,frequency domain and time-frequency domain.The influence of ambient temperature on scattering signals of ultrasonic SH wave was studied.And the compensation method of ambient temperature was proposed and applied to crack trend analysis of monitoring signal.The cluster analysis method of monitoring signals was proposed to classify the collected signals when there was no benchmark.And the basic correspondence between monitoring signals and crack evolution levels was preliminarily solved.In addition,field test research on the damage monitoring based on the ultrasonic Lamb wave for the front drawbar of the quay container crane was carried out in Qingdao.The delay-and-sum and data fusion method for the hole edge damage location and evaluation was developed,which solves the technical problems of the damage monitoring of the key parts of the front drawbar. |
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