Study On The Degradation Of Fatigue Properties For Corrosion Steel Specimens By Test

Due to a variety of environmental effects, the steel corrosion is a widespread phenomenon, resulting in the change in the performance of steel structures, it also affect the fatigue properties of the structure, especially the localized corrosion. So It is very useful to study the fatigue properties under corrosion environmental and the effect of localized corrosion on the fatigue life. If the prediction method of the fatigue life after corrosion is established, it can reveal the potential danger of in-service steel structure and provide a theoretical basis for the repair and reinforcement of in-service steel structure.In this paper, uncoated steel is studied, In order to obtain corrosion steel specimens, two methods are used, one is the composite method of spraying hydrochloric acid,the other is the method of constant temperature and humidity in a box. In contrast with the corrosion specimens in natural environment, it found that the method of constant temperature and humidity has the character of acceleration, fitness and recurrence etc, so this method can meet the requirements of rapid corrosion test.The depth of localized corrosion, the shape of localized corrosion, and the number of localized corrosion etc. all have great randomicity. In this paper, the roughness testing instrument is used to test the surface profile of corroded specimen, and the fractal theory is used to solve the characterization of the localized corrosion, meanwhile, the surface characterization of specimens in natural corrosion and in the method of constant temperature and humidity are described.The fractal dimension of the corrosion specimen is obtained by structure function, and two kinds of specimens are studied in this paper, one is the specimens in natural corrosion, the other is the specimens in the method of constant temperature and humidity. The relationship between the fractal dimension and the corrosion rate, the fractal dimension and the average localized corrosion depth, the fractal dimension and the variance of localized corrosion depth are obtained. And the result indicates that the fractal dimension is decreasing with the corrosion rate increasing.In virtue of the roughness testing instrument, the calculation method of thickness for uniform corrosion and local corrosion is proposed, at the same time, the relationship between the corrosion rate and the lost thickness is obtained.The characterization of surface properties(the fractal dimension D) is researched, and the relationship between the fractal dimension D and the fatigue life is obtained, so it provide a new prediction method of the fatigue life.