دانلود رایگان مقاله تحلیل شکست یک کابل فولادی پیش تنیده یک پل معلق

Abstract

This paper presents results of a failure analysis study to characterize the damage phenomenon that occurred in prestressed steel cables of a suspension bridge. This study includes: material characterization using chemical, microstructural and hardness analysis; fractographic analysis by scanning electron microscopy (SEM); mechanical tests of the material in static tension; fatigue tests (S–N curves) and fractographic analysis of fatigue fracture surfaces. The fatigue tests were carried out in laboratory air only and in the laboratory air also but after previous exposure in tap water to simulate the working environment of the cables. Fractured surfaces of the rods were of brittle failure type and also of cup and cone type. Due to the characteristics of the work environment (close to a river) stress corrosion was also observed and it is likely oxygen embrittlement was obtained. Results from fatigue tests and fractographic study allow to the conclusion that the main cause of cable failure, which led to a collapse of the bridge, was stress corrosion cracking (SCC).

6. Conclusions

Using the microstructural analysis, were not detected differences between the intrinsic microstructures shown by specimens taken from fractured rods fail by different mechanisms, or between samples obtained from the same rods near fracture zones and on distant zones. Were not detected evidences of the contributions from original or microstructural defects due to material itself, or to processing such as possible responsible failure of cable, which should then be given to mechanical and environmental conditions during the service. For both conditions analysed in the fatigue tests (with and without initial corrosion) a great dependence was found between the fatigue life and the maximum stress in the fatigue cycle, i.e. a small variation in the applied stress causes a great variation in the fatigue cycle. The fractographic analysis showed that the failure of the cable occurred in two phases: at first the rods were being attacked by stress corrosion seriously affecting more than 50% of the rods, which progressively took them to fracture; when the number of remaining rods no longer met the efforts applied, they broke by ductile fracture.