Mode I and mode II fatigue crack growth
resistance characteristics of high
tempered 65G steel
Authors: Lenkovskiy T.M. , Kulyk V.V. , Duriagina Z.A. , Kovalchuk R.A. , Topilnytskyy V.H. , Vira V.V. , Tepla T.L. 
Published: August 2017

Purpose: To investigate the fatigue crack growth at normal tension and transverse shear
of 65G steel with the high tempered martensite microstructure and to build an appropriate
fatigue crack growth rate curves. To determine the main and auxiliary fatigue crack growth
resistance characteristics, which are necessary for machine parts life-time estimation at
rolling contact fatigue conditions.
Design/methodology/approach: For determination of fatigue crack growth resistance
at normal tension a standard compact specimens with edge crack were tested using a
hydraulic testing machine and fatigue testing at transverse shear were performed on the
I-beam specimens with the edge longitudinal crack using the original testing setup. For
crack growth measurement an optical cathetometer B-630 was used. The crack growth rate
V was calculated as crack length increment during loading cycles. The stress intensity factor
range K was determined by dependence "K = (1 – R)Kmax accordingly to the standard test
methods. To establish crack faces friction factor at transverse shear fragments of fractured
beam specimen containing crack faces were cut out and tested as a friction pair according
to Amontons Coulomb's law. On the base of test results the fatigue crack growth rate curves
in logarithmic coordinates "K vs. V were built. These graphical dependencies for normal
tension and transverse shear were used for determination of fatigue crack growth resistance
characteristics: fatigue threshold "Kth, fracture toughness "Kfc, "K1-2 and "K2-3 which
indicates the beginning and the end of middle-amplitude region of curve, "K*, parameters
C and n of Paris’s equation. Metallographic and fractographic analyses were performed on
the scanning electronic microscope Zeiss EVO 40XVP.
Findings: Empirical dependences of the stress intensity factor range on fatigue crack
growth rate at normal tension and transverse shear of 65G steel with the high tempered
martensite microstructure are obtained. Based on these graphical dependencies the
fatigue thresholds and fracture toughness as well as the parameters of Paris’s equation are
determined.
Research limitations/implications: The fatigue crack growth on 65G steel under
low-, medium- and high-amplitude cyclic loading at normal tension and transverse shear
was investigated. The fatigue crack growth rate values for a wide range of stress intensity
factor are estimated. On the base of fractographical analysis the features of fracture of
high tempered martensite in 65G steel at transverse shear are studied. It is shown that the
transverse shear crack faces friction factor for high tempered martensite structure is less
than for low tempered martensite.
Practical implications: Using the fatigue crack growth resistance characteristics of 65G
steel at normal tension and transverse shear and related fatigue crack growth rate curves
it is possible to predict the life-time of machine parts made of steels with high tempered
martensite structure, working at rolling contact fatigue conditions.
Originality/value: Complete fatigue crack growth rate curves of 65G steel with tempered
martensite structure at normal tension and transverse shear are built and the fatigue crack
growth resistance characteristics for both modes of fracture are determined for the first time.