Expectation method for fatigue limit of used rail on railway by surface roughness and effect of difference of various fatigue test methods

Abstract

In order to estimate the fatigue strength of used rail of railway, bending fatigue test of actual rail and plane bending of element specimen are conducted. In this paper, we discussed difference of results on each test methods from the viewpoint of fracture mechanics. Also, we proposed a simple method for estimating fatigue limit considering surface roughness of rust surface and residual stress. These results are as follows;(1) As a result of conducting bending fatigue test of actual rails, plane bending and uniform tensile fatigue test of element specimens, it was confirmed that respective fatigue strengths were different. (2) √ area and surface irregularities formed by rust on bottom of used rail were measured. As a result of estimating stress intensity factor with these parameters considering stress generated in each fatigue test, it was confirmed that the stress intensity factor differs depending on each fatigue test method, and that affects the fatigue strength. (3) It was shown that the difference in the dimensions of actual rail and element test piece affects the residual stress and size of corrosion hole existing in each test piece, which in turn affects the fatigue limit. (4) We proposed a simple method for predicting the fatigue limit of used rails, considering the residual stress and the estimation result of extreme value statistical analysis for maximum roughness Rz.

Keywords

• railway
• rail
• fatigue limit
• fatigue stregth
• stress intensity factor
• bending fatigue test
• plane bending fatigue test
• uniform tensile fatigue test
• maximum roughness