| Cranes are widely used in port, shipbuilding, railway transportation, metallurgical industry etc. With the crane in large-scale development, in order to reduce weight, the high strength steel was gradually adopted instead of the low strength carbon steel used in the past. But the high strength steel is sensitive to material defects, and fracture toughness is low, and easy to brittle. Especially for the portal crane, its working condition is very heavy, and its load is complex and changeable, and significantly impacts the dynamic properties of whole machine. After a period time in use, there will be cracks, as the cracks extend fracture failure will occur. Relevant statistical data also shows that the crack is the main fault of crane metal structure. But due to the specific conditions of the port and equipment renewal fee restrictions, a lot of old cranes with cracks damage in port are busy with first-line work, reducing the safety of production. So the calculation of the fatigue life of crane metal structure and the residual life of crack propagation is necessary.This paper chooses the jib structure of the portal crane as the object of study on fatigue and fracture. Obtain the load-time history of the jib structure by establishing virtual prototype model of the portal crane, and analyse the fatigue and fracture of the jib structure through the load spectrum combined with the theory of fatigue and fracture, using the CAE computer technology. A method of raising the fatigue strength of jib structure is proposed by, monitoring methods of crack growth and repair methods of crack, then use the method of numerical simulation to verify redeeming effect of crack repair. The research method of this paper can provide a new method and reference for the design and maintenance of the crane.The research content and the main results are summarized as follows:(1) According to characteristics of structural form, technical parameters and operation of the portal crane, the rigid and flexible coupling model of the portal crane is established in the ADAMS software. Dynamics simulation is carried out in the ADAMS, to obtain the load-time history of jib structure of the portal crane. At the same time, in order to provide an accurate load-time history for the analysis of fatigue damage to jib structure, verify the correctness of the load-time history, according to analyse the force of jib structure.(2) Analyse the fatigue of jib structure in the Fe-Safe software, combining the results calculated in the ANSYS software and the load-time history of jib structure. After the simulation, obtain the fatigue life contour of jib structure and the safety coefficient of fatigue life contour relative to the design life, then propose the method of raising the fatigue strength of jib structure.(3) Obtain the crack position of jib structure by the analysis results of the Fe-Safe software. Using the interface technology between ADAMS and ANSYS, the stress-time history of crack positons are calculated in the ANSYS. Then according to the fatigue crack propagation formula of Paris, the residual life of the fatigue crack is calculated, and put forward the monitoring method of crack growth.(4) Propsed the crack repair methods which are suitable for the crane structure, then use the method of numerical simulation to verify redeeming effect of crack repair. |
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