Analysis of Propagation of Fatigue Cracks in Crane Girders

Abstract

The results of analysis results of residual life of crane girders with operational defects based on numerical studies of the stress-strain state, the equations of limiting states, and the kinetic dependences of fatigue crack propagation formulated under criteria of strain and fracture mechanics are presented. A high level of wear of the fixed capital assets of engineering structures and metal constructions, as well as operation of the facilities in beyond-design-basis terms, contributes to origination of emergencies caused by damage accumulation. Crane girders operated under emergency conditions caused by the presence of fatigue cracks of different length in the most dangerous zones of the girder wall with an eccentric application of crane load are studied. According to the results of a numerical experiment, the lines of stress intensity influence at the crack tips appearing at the upper zone of the wall when different values of loading eccentricity caused by the rail displacement from the vertical axis of girder cross section were revealed. The dependence of the fatigue crack length and of the stress intensity at the crack tip on the number of load cycles of the girder is determined. To evaluating the bearing capacity of crane girders operated in emergency conditions, it is proposed to use the effective values of the stress intensity factors calculated for specific loading conditions, taking into account the structural features of the girders, the sizes of emerging fatigue cracks, and their locations in the crane girders. According to the results of analysis, the diagrams making it possible to predict the remaining residual life of crane girders with a crack are constructed. On the basis of traditional design procedures of structures for cyclic crack resistance, the calculation algorithm for individual life of crane girders which includes the obligatory analysis of the stress-strain state of the crane girder with a crack at the upper zone of the wall is formulated and implemented.