Purpose: The aim of the proposed research is to establish experimentally the relation between
damaging of the tread surface of model wheels and the characteristics of fatigue crack growth
resistance of wheel steels "KI th, "KII th, "KI fc, "KII fc), depending on its microstructure.
Design/methodology/approach: Characteristics of the fatigue crack growth resistance
have been determined on the specimens cut out from the hot rolled plate of thickness
10 mm of the steel which is an analogue of railway wheel steels. To obtain different steel
microstructures and its strength level, test specimens were quenched (820°C, in oil) and then
tempered at 400°C, 500°C, and 600°C for 2 h. The characteristics of Mode I fatigue crack
growth resistance of steel were determined on the basis of fatigue macrocrack growth rate
diagrams da/dN–"KI, obtained by the standard method on compact specimens with the
thickness of 10 mm at a frequency of 10-15 Hz and the stress ratio R = 0.1 of the loading
cycle. The characteristics of Mode II fatigue crack growth resistance were determined on
the basis of da/dN–"KII diagrams, obtained by authors method on edge notched specimens
with the thickness 3.2 mm at a frequency of 10-15 Hz and R = –1 taking account of the crack
face friction. The hardness was measured with a TK-2 hardness meter. Zeiss-EVO40XVP
scanning electron microscope was used for microstructural investigations. Rolling contact
fatigue testing was carried out on the model specimens of a wheel of thickness 8 mm and
diameter 40 mm in contact with a rail of length 220 mm, width 8 mm and height 16 mm.
Wheels were manufactured form the above-described steel after different treatment modes.
Rails were cut out from a head the full-scale rail of hardness 46 HRC. The damaging was
assessed by a ratio of the area with gaps formed by pitting and spalling to the general area
of the wheel tread surface using a special stand.
Findings: The growth of the damage of the tread surface of the model wheels correlates
uniquely with the decrease of the cyclic fracture toughness of the wheel steel "KI fc and
"KII fc, determined at Mode I and Mode II fracture mechanisms. These characteristics of the
wheel steel can be considered as the determining parameter of this process, in contrast to
the fatigue thresholds "KI th and "KII th.
Research limitations/implications: Investigations were conducted on model wheels
that simulate the damage of real railway wheels tread surface.
Practical implications: A relationship between the damage of tread surface of railway
wheels and the strength level of wheel steels is determined.
Originality/value: The damage of the tread surface of the model wheels during the rolling
contact fatigue of the pair wheel-rail increases with the growth of the strength (hardness) of
the wheel steel, which corresponds to the statistical data of the operation of the real railway
wheels.
A study of wear and rolling contact fatigue on a wheel steel in alternated dry-wet contact aided by innovative measurement systems