Study On Crack Propagation Characteristics Of Metal Structure Of Hoisting Machinery Based On Infrared Thermography

To promote the process of The Belt and Road and Made in China 2025,China’s ports are developing rapidly.At present,China’s major ports are transforming into intelligent ports based on the concept of innovation-driven,which is developing in the direction of informatization,intelligence and automation.At the same time,as an integral part of port logistics transportation,port hoisting machinery is developing towards large-scale,complex,automatic and intelligent.Due to the high design and manufacturing cost,some ports have extended the use of hoisting machinery that should have been retired to save costs.According to the detection results of Wuhan Port Machinery Quality Inspection Center,it is found that the metal structure of the hoisting machinery in service has defects like appeared fatigue damage,fatigue crack,corrosion and other defects,which makes the operation of the hoisting machinery under complex load have safety hazards.The study of the fatigue failure and fatigue propagation growth rate of the metal structure of lifting machinery is of significance.During slow crack propagation,stress concentrations are generated at the crack tip,while a large amount of plastic work is consumed in the crack propagation zone.With the dissipation of plastic work,even for very slow propagating cracks,temperature fields and acoustic emissions are generated on the surface of the metal structure.The commonly used method for detecting the temperature field of metal structures is infrared thermography,which is concerned by scholars because of its non-contact detection,large detection range and high efficiency.This thesis investigates the crack propagation characteristics of the main metal structures of hoisting machinery based on infrared thermography.The main contents are divided into three parts as follows:(1)In this thesis,the infrared thermography is introduced to the study of fatigue crack propagation of metal structure of hoisting machinery.Firstly,the basic principle of infrared thermography and infrared imaging system are introduced.According to the law of thermodynamics,the thermal-mechanical coupling equation of the crack tip,the equation between stress and temperature of the crack tip and the equation of inherent heat dissipation source at crack tip are derived.Then the stress-time curve of the hoisting machinery metal structure measured in the field is analyzed to obtain the load spectrum.And the load for the fatigue crack propagation test is determined.During the fatigue crack propagation test,the infrared temperature field data of the crack tip is recorded using an infrared thermal imager.This data is then substituted into the equation to obtain the inherent heat dissipation source of the crack tip at a specific time.(2)In this thesis,a fatigue crack propagation model based on energy method is proposed.Firstly,the quantitative relationship between fatigue crack propagation rate and energy dissipation rate is derived from the energy method.Then,the energy dissipation rate is obtained by calculating the inherent heat dissipation source of the crack tip.This data is fitted with the test data to obtain a linear relationship between the crack propagation rate and the energy dissipation rate,which verifies the proposed fatigue crack propagation model based on the energy method.(3)In this thesis,the surface temperature field data of the crack propagation process of Q235 specimens under uniaxial loading is analyzed in the finite element software ABAQUS using the fully coupled thermal stress analysis method.According to the finite element analysis results,the load-displacement curve and the crack tip temperature variation curve are matched well with the test data,which verifies the fully coupled thermal stress analysis method of the finite element software.Then according to the results of finite element analysis,the effects of plastic work conversion coefficient and tensile speed on the surface temperature of Q235 specimen are verified.Based on the energy dissipation rate model proposed in this thesis,the fatigue crack propagation rate can be predicted.Therefore,it is expected to realize the realtime monitoring and evaluation of the fatigue damage and fatigue crack propagation of the metal structure of hoisting machinery using infrared thermal imager to ensure the safe production of ports.