Fatigue Life Research For Box Girder Of Crane

With the development of modern industry and lifting transportation industry, bridge and gantry crane (call crane for short in the following) has become one of the indispensable special equipment. And bridge crane girder is a typical welding structure; due to the alternating load in daily work, these expanding defects can easily produce visible cracks, if you don’t take timely measures to remedy, it is likely to lead to fatigue failure.Fatigue damage is often caused by cracks and extension. Fatigue life of crack initiation and formation is short; the fatigue life mainly depends on the crack extension stage. The goal to researching fatigue analysis approaches is to reduce the dependence of fatigue analysis to the study of a large number of trials, reducing experience in the process of composition. Therefore, carrying on fatigue crack propagation mechanism research to the welding and the residual life prediction of box girder can prevent the happening of the accident of fatigue fracture, and to the design, fabrication, inspection and management of the bridge crane has important guiding significance.The main content in this paper as follows:1. Applying the allowable stress and the finite element analysis method for metal structure theoretical calculation, to ensure the crane of stiffness, strength and fatigue strength of dangerous parts are in the range of allowable values specified in crane design specification (GB/T3811-2008).2.Exploring the cause of bridge crane fatigue crack, discussing the changing rule of the stress field and displacement field near these cracks, Stress intensity factor plastic correction of the small scale yielding was deduced.3.Combining fracture mechanics and Miner mechanics in damage mechanics, the fatigue life to welding box beam bridge of overhead travelling crane is deduced under constant amplitude load and amplitude load, Hot spot stress method are introduced to estimate the bridge crane metal structure fatigue life of variable cross-section.4. According to the rules of the fatigue strength analysis method based on the stress ratio, VB program is compiled to the fatigue calculation of crane bridge structure.5. Subjective evaluation index system of crane is established and the weight value is calculated with the analytic hierarchy process (ahp), then use fuzzy comprehensive evaluation theory to fuzzy calculate, finally using the weighted average method to get security value to judge the fatigue state of the crane. Results match the actual almost.