Influence of 65G steel microstructure on crack faces friction factor under mode II fatigue fracture

Abstract

Purpose: The aim of the paper is to evaluate the dependence of microstructure parameters,strength and plasticity of steel on crack faces friction factor.Design/methodology/approach: The specimens for the investigation were cut out fromthe 10 mm thick hot-rolled plate of 65G steel used as a model material for fatigue anddurability testing of whole-rolled railway wheels. The mechanical characteristics of the steelwere determined according to the state standard using cylindrical specimens of diameter5 mm and effective length 50 mm. The specimens were heat-treated at the mentionedconditions. Fatigue testing under mode II loading was carried out on a special rigid loadingmachine in the standard laboratory conditions at symmetric sinusoidal cycle with a frequencyof 12 Hz in the range of fatigue crack growth rates da/dN = 5∙10-8…5∙10-7 m/cycle untilits reaches relative length l/b ≥ 0.8. The obtained microsections were investigated using theoptical metallographic microscope Neophot 9 equipped with a digital camera Nikon D50 andelectronic scanning microscope Zeiss EVO 40XVP. Hardness of the specimens with differentmicrostructure was determined using durometer TK-2. The crack faces friction factor wasdetermined using original device for fractured surfaces sliding under certain compressionforce realizationFindings: The dependences of microstructure parameters, strength and plasticity of steelon crack faces friction factor are obtained.Research limitations/implications: The investigation of the influence of microstructureparameters, strength and plasticity of real wheel steels on crack faces friction factor at themode II fatigue crack growth will be carried out.Practical implications: The value of crack faces friction factor have strong impact onstress intensity at the crack tip and must be taken into account at crack growth rates curvesplotting.Originality/value: Mode II fatigue crack faces friction factor of steel is firstly experimentallydetermined.

A new approach for evaluating the resistance of wheel steel to spall formation

“…where l -total crack length, b -basic dimension fccrack faces friction factor. To establish crack faces friction factor fc at the transverse shear fragments of fractured I-beam specimen containing crack faces were cut out and tested as a friction pair according to Amontons Coulomb's law using the original device and technique described in [18]. On the base of test results, the fatigue crack growth rate curves in logarithmic coordinates ∆K (∆KІ for normal tension and ∆KІІ for transverse shear) vs. v were built by approximation of the experimental data points with S-lines.…”

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