Fatigue Crack-Growth Resistance of Thermally Hardened 65G Steel Under Transverse Shear
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FATIGUE CRACK-GROWTH RESISTANCE OF THERMALLY HARDENED 65G STEEL UNDER TRANSVERSE SHEAR T. М. Lenkovs’kyi
UDC 620.178.3: 539.421.2
We plot the kinetic diagrams of fatigue fracture of 65G steel under the conditions of transverse shear after different modes of heat treatment within the range of fatigue crack-growth rates covering six orders of magnitude with the use of the stress intensity factor for the evaluation of the stress-strain state in the vicinity of the crack tip. The main and auxiliary characteristics of cyclic crack-growth resistance are determined with regard for the friction of the lips of a fatigue crack. We construct the diagrams of structural strength and confirm the hypothesis that the fatigue thresholds increase with the yield strength of 65G steel under the conditions of shear. Keywords: transverse shear, kinetic diagram of fatigue fracture, cyclic characteristics of crack-growth resistance, shear strength, diagram of structural strength, fatigue threshold.
In order to predict and guarantee the designed service life of machine parts and elements of the metal structures operating under cyclic loads, it is necessary to know the fatigue crack-growth (FCG) resistance of structural steels. Hence, the methods of fracture mechanics based on the construction of the kinetic diagrams of fatigue fracture (KDFF) of steels and the determination of the characteristics of their cyclic crack-growth resistance (CCGR) are widely used in the scientific and engineering practice. In the case of fracture according to the mode-I macromechanism, the KDFF were constructed for various classes of structural steels and the CCGR characteristics determined on the basis of these diagrams now play the role of reference data. However, the fracture processes in the materials of machine parts operating under complex cyclic and dynamic loads run according to the mixed and shear macromechanisms [1–5]. In particular, in the case of rolling accompanied by the formation of defects in the form of exfoliations under the conditions of contact fatigue, the macromechanism of transverse shear (according to this mechanism, the lips of a propagating crack shift in the direction perpendicular to its front) is predominant [1, 6–10]. This is why to guarantee the serviceability of products under these conditions, it is necessary to choose optimal materials with regard for their CCGR characteristics under the conditions of transverse shear. In the literature, the information about these materials is quite poor, and the number of diagrams in the form of dependences of the CCGR characteristics on the strength characteristics of steels is insufficient. The aim of the present work is to determine the CCGR characteristics of 65G steel after different types of heat treatment on the basis of the KDFF in transverse shear and plot the diagrams of structural strength. Equipment and the Procedure of Investigations Tested specimens were made of hot-rolled plate made of 65G steel with a thickness of 10 mm. To obtain steels of different strengths, the specimens
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