| Grab Unloader belongs to the gantry crane in the directory of national special equipment.It is one variety of the unloader equipment，which seriously involves life safety and risk. Thefailure of grab unloader is mostly resulted by the fatigue failure of structure under alternatingstress. So the remaining life analysis of grab unloader plays an important role in the operationand repair management system.Based on the theory of finite element and fracture mechanics，firstly a35t,1800t/h,sgrab unloader is selected as the research object from practical engineering of the author’swork field. The pre-process of finite element software Hypermesh is used to establish themodel of the grab unloader, and the calculation of its deformation and static stress in differentoperating modes is made by MSC.NASTRAN software. The static strength and rigidity arechecked and meet the requirement.Then, the fatigue life of the grab unloader with the fatigue analysis software nCodeDesignLife is analyzed, and the cloud fatigue life distribution under the condition of no defectand normal usage of the crane is achieved.Finally, the mechanism of fatigue crack propagation is investigated, and the problem ofcrack growth life is solved by the Paris formula. According to the charactersitic of the grabunloader, the crack propagation life is regarded as the fatigue life of the grab unloader, whichis consistent with the results of finite element analysis. It is found from the NDT(no defecttest) that the fatigue crack starts from the maximum stress point of the grab unloader. Thecycled times to failure are calculated with fracture mechanics during the crack growing. It isonly6.1%difference compared with the actual operation times provided by the company. Therelationship of extended life with initial crack and operation cycles on the crack are analyzed,which provides an important reference for inspection and repair design. |
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