The statistical characteristics of the rail steel wear in conditions of fretting-fatigue

A method of processing the results of tests for fretting fatigue drawn on the literature, is presented to determine a quantitative measure to be used in assessing the surface wear resistance in conditions of contact cyclic loading. Operation practice and experiments indicate to multiple micro-cracks of different sizes present on the contact surface. An assumption is made regarding the accidental character of the crack birth thus making possible the use of the mathematical statistics to obtain the characteristics treated as the mechanical properties of the crack resistance, which assess the resistance of contact fatigue material. The samples of three steel grades used for railway rail production are studied. The wear resistance is assessed through robust statistical characteristics under the assumption that occurrence of the surface defects is a random process. The loading is carried out in conditions of rolling friction with the balls spinning in the mandrel, thus forming an annular wear pad. As the load on the test rig is considered an analogue of the force action of the wheel on the rail, the wear resistance can become a quantitative measure of the quality of the rail steel. Measurements on each sample were made for three runs. The curves of the density of the defect area distribution on the wear surface of the samples are presented. Quantitative characteristics are proposed to estimate the fretting fatigue resistance of the metal, namely, the average crack area, standard deviation and the variation coefficient. Those characteristics are the parameters of statistical processing of experimental observations of the number and size of the surface cracks that occur under cyclic loading of the metal surface. The degree of significance of the observed damages is discussed to be used as an indicator when comparing different steels in the wear resistance. The results of the experiment made it possible to arrange three studied steels in a series of their fretting corrosion resistance: the Japanese steel has the greatest resistance to contact wear, then Russian steel and then Polish steel that exhibits the least resistance to contact wear.

1. Botvina L. R. Fracture. Kinetics, mechanisms, general regularities. — Moscow: Nauka, 2008. — 334 p. [in Russian].

2. Botvina L. R., Levin V P, Zharkova N. A., Tyutin M. R., Soldatenkov A. P., Demin Yu. A. Kinetics of damage accumulation pearlitic rail steel under contact fatigue / Trenie Iznos. 2016. Vol. 37. N3.P 309 - 317 [in Russian].

3. Morozov E. M., Zernin M. V A contact problem of fracture mechanics. — Moscow: Mashinostroenie, 1999. — 544 p. [in Russian].