Characteristics Of The Fatigue Fracture Life Of Bridge Crane Under Constant Amplitude Load

Bridge crane plays a very important role in modern society, and it is a kind of special equipment which used widely in the economic construction departments. Meanwhile, the accidents caused by failure of the bridge cranes has caught people's attention increasingly. Of all kinds of failures, the most important is the fatigue fracture bridge crane beam. Study the problems of fatigue and fracture with the method of fracture mechanics, generally set the crack propagation parameters as approximations, and then the crack propagation life will be determined. But in reality, due to the randomness of material properties, structure sizes, initial crack size, critical crack size,environment and other parameters, so that the fatigue life calculation bridge crane into a complex statistical issues.To resolve the above problems, this paper studied the bridge crane fatigue endurance properties with the method of CT test, numerical simulation of Matlab and Ansys parametric modeling and analysis,.First, studied the fatigue parameters by CT test. And determined that the random distribution characteristics fatigue crack growth rate parameters at room temperature with the a-N curves of Q235 specimens and the secant method.Secondly, build the model of a three-stage fatigue crack growth based on Matlab software, which divided the process into surface crack, center crack and edge crack. Combine the method of Monte-Carlo random sampling with characteristics of random test results obtained in the CT study to analyze the bridge crane web- life characteristics of the crossbeam weld crack three-stage probability and its influencing factors. It shows that, the initial crack depth desired surface has a great influence on the final assessment of the life, and the percentage of surface crack propagation time spent in fatigue crack propagation large share of the total life, especially in large thickness,experience after penetrating the surface cracks can be considered to achievethe structural damage, but can be ignored through the crack propagation time.Finally, analysis the crack propagation of bridge cranes to determine the location of the bridge crane most prone to cracking with Ansys software. And proposed a kind of life assessment in Ansys finite element method based on Paris formula, and build the web- parametric model to simulate actual working conditions overhead crane and crack propagation at the bottom flange plate with APDL language. In addition, calculate stress intensity factor with the interaction integral method in Ansys, which fit the number of stress cycles bridge crane under constant amplitude loading- crack length relationship effectively, and in line with the law of crack growth, improve fatigue life calculation accuracy.