Assessment And Analysis On Fatigue Total Life For Crane Lattice Boom

The crane is necessary equipment in industrial production. Lattice boom crane is an important part of the crane, it is widely applied, and its’fatigue life assessment is increasingly becoming an engineering problem to be solved. The lattice boom is composed of chords and webs’intersection, its’structure is complex and stress is composite stress, so we could not calculate the stress accurately, leading to security risks. So the assessment of fatigue life is very important.From the process of fatigue failure, the fatigue crack initiation life and fatigue crack propagation life are assessed based on the tested load spectrum, and assessment algorithm is established too. And then the influencing factors of fatigue crack initiation life and fatigue crack propagation life are researched and analyzed. The main work of this article is as follows:(1) The crane fatigue crack initiation life assessment algorithm is established by the method of local stress and strain and modified Neuber method, and the determination of stress concentration factor and load spectrum’s loop count are described too.(2) According to the boom structural features and safety requirements, the assessment model of crack propagation life is established based on fracture mechanics, and the calculation method of the chords and webs’intersecting stress intensity factor is modified.(3) In this paper, the QLYS25HZ crane boom is analyzed by FEM, and the typical working conditions are determined based on the strength and practical experience. Combine with analysis result, the paper could get the stress spectrum of fatigue dangerous point by boom site response testing.(4) In order to obtain the total fatigue life, fatigue crack initiation life and fatigue crack propagation life of QLYS25HZ crane boom are assessed, according to the tested load spectrum.(5) The paper proposes some design recommendations by researching and analyzing influence regularity and size of the crack initiation life factors; according to the calculation of crack propagation life, the crack propagation process and the influence of the initial crack length are analyzed.In this paper, the fatigue crack total life assessment algorithm of the lattice boom are established, which can assess boom life conveniently and reasonable. This provides a new way of assessing fatigue life.