THE SIZE EFFECT ON FATIGUE STRENGTH OF STRUCTURAL STEEL MATERIALS IN HIGH-HUMIDITY ENVIRONMENT
Keywords:
Fatigue strength, structural steel, high-humidity environment, crack length, fatigue test.Abstract
Fatigue tests under rotating bending fatigue testing machine has been carried out to estimate the size effect on fatigue strength of structural steel materials in high-humidity environment. The size and geometry of the specimens were in accordance with specifications of ASTM E-466. The specimen contains a shallow notch to observe crack initiation. The specimen surface and shallow notch were ground with grade 1200 emery paper and then were buff finished. The tests were carried out a variation of diameter size specimens from 8 mm, 2 mm, and 1 mm in humidity environment with 60 % relative humidity, 70 % relative humidity, 80 % relative humidity and 90 % relative humidity. The results show that the fatigue strength increases with decreasing specimen size from diameter of 2 mm and 1 mm of SS400 and S45C steels in high-humidity environment. Ion-exchanged water remarkably reduces the fatigue strength of these steels. The initiation and propagation behaviors of micro cracks were investigated on the specimen surface. Cracks were observed by a scanning electron microscope (SEM).References
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