[en] The influence of temperature within the range of 20 to -120 deg on the endurance limit and the notch sensitivity of 10GN2MFA steel was examined. It has been shown that as temperature decreases and the material passes over from the viscous state into the brittle one, the temperature dependences of the mechanical properties retain their monotonous character. In the case of the viscous-to-brittle transition, there is observed an abrupt decrease in the relative duration of the development of a crack under stresses that are near to the endurance limit

[en] A procedure is suggested for crack resistance test under static and vibration loading in corrosion medium. The tests show that stainless steel 15Kh12N2VMF is not subjected to corrosion cracking in sea-salt solution, a long-term exposure (720 h) does not reduce the thresho d stress intensity factor under cyclic loading, static overloading results in delaying the crack (independent of overload,time in corrosion medium) but the threshold stress intensity factor does not increase under these conditions

[en] A procedure is suggested for experimental determination of the stress intensity factor for surface bend-caused fatigue cracks of 2c/πD-0.004-0.5 relative length (2c is the crack surface length, D is the specimen diameter) in smooth cylindrical steel specimens. The procedure is based on an assumption that dependence of the fatigue crack propagation rate on the stress intensity factor is equal for calibrated and standard specimens. When the relative crack length is large, results obtained with the procedure concerned are in good agreement with data measured using the method of elastic flexibility of crack-bearing specimens

[en] The previously formulated model of fatigue failure of metals which is based on consideration of the yield point reduction in the surface layers and on the critical size of the nonpropagating crack under cyclic loading is experimentally checked for cases of stress concentration and asymmetric cyclic loading. Experiments are carried out under symmetric bending of 20Kh13 steel and titanium alloy specimens with a semicircular notch of 0.1 and 0.3 mm radius as well as under asymmetric loading of 20Kh13 and 08Kh17n6t steel specimens. A possibility is shown to evaluate a decrease in the fatigue limit of compressor blades for the turbine engine with corrosion pits on their surface, the depth of pits being known

[en] Rate and fractographical peculiarities of fatigue fracture under conditions directly preceding brittle fracture have been studied. The investigations are carried out using a low-carbon low-alloyed steel of ferritic-pearlitic class with 0.1% C at the temperatures from -120 to -190 deg C and steel 45 in a high-strength state (after quenching and low tempering) at normal temperature. It is established that in a carbon steel after low tempering crack propagation before final fracture takes place according to quasi-cleavage mechanism which considerably accelerates the process of fatigue fracture. In a ferritic-pearlitic steel which is in a brittle state at low temperatures the rate of crack propagation process according to the fatigue striation mechanism is significantly lower

[en] Metal fatigue fracture model based on account of surface layer properties and on criteria of crack mechanics is developed. Fatigue strength is defined by the surface layer depth and stress intensity threshold coefficient, characterizing conditions of crack initiation. These two conditions and representation of corresponding equations permit to give a qualitative estimation of the effect on fatigue strength of scale, stress concentration, residual stresses, cycle asymmetry, and to also to explain accelerated propagation and the following retardation of small surface cracks

[en] The obtained data on the anomalous decrease of the yield point near the material surface with regard for characteristics of cyclic crack resistance are used to formulate a model of fatigue material failure. The model permits calculating a fatigue limit either of a specimen or of a construction according to a noncritical nonpropagating crack under bending, tension-compression for objects of different thickness and shape with notches of different depth with the presence of residual stresses and loading cycle asymmetry

[en] Effect of anomalous properties of surface layers in metal materials on their fatigue strength is reviewed. Experiments on 20Kh13, 15Kh12N2VMF, 08Kh17N6T steels and titanium VT3-1 alloy show that the flow on the specimen surface begins at stresses amounting to 30...40% of the integral yield strength. The sea salt solution decreases a stress of the flow on the surface of steel specimens about 1.5 times and does not affect this characteristics in the titanium alloy specimens. Experiments on single crystals of pure nickel, where slip lines under plastic strain are seen, confirm a decrease in the level of the flow stress in the presence of the sea salt solution

No abstract available

[en] Conditions of transition to a critical state (complete failure) are studied for 15Kh2NMFA steel as based on energy analysis of the crack discontinuous propagation under cyclic loading. It is established that depending on the ratio of critical stress intensity factor, at which threre occurs a brittle ump of the crack, and dynamic fracture toughness of the material, the jump length is controlled either by the size of the damaged zone at the ctack or the system elastic energy storage. Changes in the stress intensity factor during the crack jump under cyclic loading are calculated and a possibility for predicting the crack jump length under these conditions is shown