Research Of Multiscaling Fatigue Fracture Behavior Of Cable Steel Wires In A Long-span Cable-stayed Bridge

With the rapid development of bridge technology, the large span bridges such as cable-stayed bridge and suspension bridge have been widely applied, in which cables are the main structural components. Many environmental and material factors such as erosion, natural disasters, load long-term effects, fatigue, creep and material aging would inevitably increase the damage accumulation and reduce the loading capacity of structural components. If the degradation exceeds the loading capacity, the catastrophic event would occur that is a very serious threat to the people's life and social wealth. Hence, the fatigue failure problem of cables in large span bridges gains more and more attentions. In this paper, the existing approaches for fatigue failure analysis are summarized. Then, the multiscaling crack growth model is employed to investigate the fatigue fracture behaviors of cable steel wires in a cable-stayed bridge.The main work in this paper includes a multiscaling crack growth model from micro- to macro-scale based on the restraining stress zone is established. The analytical solution of micro/macro dual scale stress intensity factor K mmiaccrroo is obtained. By taking the dual scale strain energy density factor S mmiaccrroo as the controlling quantity, a multiscaling fatigue crack growth model is developed in this work. Hence, the whole fatigue failure process can be depicted in a consistent way by applying the proposed model. It no longer needs dividing a fatigue process into two different stages of fatigue crack initiation and propagation described by different approaches as usual. Then, the experimental S-N curves of aluminum alloy LY12 plates under different cyclic stress ratios are exactly re-produced by the proposed model. When the effects of material micro-structure are taken into account, the discrete fatigue test data can also be reflected. The results indicate that size of initial micro-defects as well as the different evolution modes of material micro-structure has a pronounced influence on the fatigue life of specimens. The microscopic effect is a main reason of the scatter of fatigue test data. Finally, Lijiasha large span bridge is taken as a real engineering example. The finite element model for the whole bridge structure is established by software MIDAS. The finite element analysis is then performed under the different loading conditions. By using the multiscaling fatigue crack growth model, the fatigue fracture behaviors of cable steel wires are calculated and analyzed. The results show that the proposed model can be valid for describing the whole fatigue process of cable steel wires from micro- to macro-scale.