Prediction of fatigue crack extension life and assessment of load reduction

In this paper, for the first time, a safety assessment process is proposed for predicting fatigue crack extension remaining life and crane load reduction use. The method is based on fracture mechanics to establish a simulation model of the main girder of a crane using on-site strain-gauge tests and related crack extension test results. Establishing a statistical model based on the real work experience of a crane, obtaining the stress-time history and load spectrum at the fatigue calculation point on the crane girder through dynamic simulation. Expansion simulations of a single initial crack with different deflection angles show that crack deflection slows down the crack expansion rate, i.e., the smaller the deflection angle, the smaller its lifetime. Expansion analyses of coplanar and adjacent parallel surfaces multicracks were also performed to investigate the effects of crack morphology changes during crack coalescence and coplanar crack interactions on crack coalescence, as well as the effects of defect spacing on fatigue life. For the single crack with a width of 4 mm, a load reduction analysis is performed, and the simulation results indicate that the load reduction range is $20\%$–$30\%$, the fatigue remaining life of the crack is increased to $2.05$–$3.08$ times the original value, the degree of load reduction and the remaining life is compliant with the GB/T 41510-2022 Safety Assessment Rules for Lifting Appliances-General Requirements general requirements for crane safety evaluation, indicating that the proposed approach in this paper for estimating fatigue crack growth life and crane load reduction is viable and offers the benefits of a short cycle and low cost.