S. T. Shtayura

Methods for the Construction of the Kinetic Diagrams of Fatigue Fracture for Steels Under the Conditions of Trаnsverse Shear with Regard for the Friction of Crack Lips

We propose the design of a specimen for the investigation of the fatigue fracture of steels under transverse shear. A formula for the determination of the stress intensity factor with regard for the friction of crack lips is obtained with the use of the finite-element method. The methods aimed at the construction of the kinetic diagrams of fatigue fracture under the conditions of transverse shear are developed and tested on specimens of 65G structural steel. We plot the kinetic diagram of fatigue fracture and approximate its middle segment by a linear dependence in the established parameters.

Investigation of the Kinetics of Fatigue Macrocracks Under Transverse Shear

We study the kinetics of shear macrocracks under the conditions of fatigue fracture by transverse shear of thermally hardened 65G steel with a troostite-sorbite structure for low-, middle-, and high-amplitude cyclic loads. We plot the kinetic diagrams of fatigue fracture with regard for the friction of the faces of a shear crack within the range of its growth rates covering up to six orders of magnitude. On the basis of the constructed dependence, we determine the principal and additional characteristics of cyclic crack resistance. We also study the contact interaction of the faces of fatigue cracks and the fractographic features of fracture under the conditions of low- and high-amplitude deformation by cyclic transverse shear.

Determination of the Parameters of Crack Resistance for 17g1s Steel Under Transverse Shear

We determine the static crack resistance of compact Richard’s specimens made of 17G1S steel and the critical crack opening displacement under the conditions of transverse shear (mode II). The specimens are tested under cyclic loading. Richard’s specimens are modernized with an aim to improve the conditions for the initiation and growth of mode II cracks. By using the digital image correlation method, we determine the distribution of strains near the notch tip.

Acoustic Investigations of the Strained State of Hydrogenated 09G2S Steel

We study the acoustic properties of inhomogeneous plastically deformed specimens made of 09G2S steel. The specimens with residual strains were successively subjected to heat treatment and hydrogenation from the gas phase. After each procedure, we measured the space distributions of the velocity of longitudinal acoustic waves. We also analyzed the mechanisms of changes in the velocity in the course of hydrogenation in the region of the specimen with residual strains.

ESTIMATION OF THE INFLUENCE OF HYDROGEN ON THE MECHANICAL CHARACTERISTICS OF 40KH STEEL

We propose a theoretical and experimental approach to the quantitative evaluation of the influence of hydrogen on the mechanical properties of 40Kh steel. We experimentally determine the characteristics of strength and plasticity and construct analytic dependences of the yield strength, true fracture stresses, and relative narrowing of 40Kh steel on the concentration of hydrogen in steel.

INFLUENCE OF STIFFNESS OF THE STRESSED STATE UNDER BIAXIAL LOADING OF TUBULAR SPECIMENS ON THE STRENGTH CHARACTERISTICS OF 20 STEEL IN HYDROGEN

We plot the diagrams of axial and tangential stresses under proportional biaxial loading used to induce the stressed states with different stiffnesses in tubular nonhydrogenated and hydrogenated (10 МРа) specimens. It is shown that, as the stiffness of the stressed state increases (χ = 0.52) under biaxial loading, the yield and fracture stresses of nonhydrogenated specimens caused by tension increase by 24% as compared with the case of uniaxial tension. In hydrogenated specimens, these stresses increase only by up to 13%. As the stiffness of the stressed state increases, the intensities of the yield and fracture stresses in cross sections of the specimens decrease. In the case of fracture of hydrogenated specimens, the indicated intensities are higher than for nonhydrogenated specimens.

Determination of the Stress Intensity Factor for a Transverse Shear Crack in a Beam Specimen

By the method of superposition of stressed states, we deduce a formula for the stress intensity factor KІІ under the conditions of transverse shear of an I-beam specimen. The comparison of the results of calculations with the theoretical data obtained earlier by the finite-element method reveals their satisfactory convergence within a broad range of relative crack lengths.

Influence of hydrogen on the fracture resistance of 65G sheet steel

We present the results of investigations of the influence of hydrogen on the fracture of 65G sheet spring steel. The distribution of strains is determined by the method of digital speckle correlation, the topography of the specimen surface in front of the crack tip is analyzed, and it is shown that the influence of hydrogen makes the fracture strain 1.5 times lower. It is also demonstrated that the crack resistance of 65G steel decreases in hydrogen (as compared with air) by 14%. The fractographic analysis of the fracture surfaces of specimens is performed and the morphology of crack propagation is investigated by the metallographic method. It is shown that the decrease in the operating characteristics of 65G steel under the action of hydrogen manifests itself in the localization of plastic strains and extensive delamination along the joints of the layers of rolling.

Fracture strength of steels under biaxial loading in hydrogen

We have studied the stress-strain state of material in the process zone, near the crack tip in cruciform specimens made of 09G2S steel under non-proportional biaxial loading. We have obtained the strain distribution in this zone, in a domain of size 6 × 4.5 mm by the method of digital correlation of speckle images. We have compared the strain distributions and critical parameters obtained in air and hydrogen. It has been established that, under biaxial loading, the critical stress intensity factor KC, critical crack opening δC, and critical strain εC near its tip vary within the limits of 15, 47, and 40%, respectively, depending on the parameter of loading rigidity κ. For hydrogen, we have detected a shift of the maximum of the dependence PC vs. parameter κ to the side of its positive values. The maximal effect of hydrogen on δC and εС is observed under uniaxial tension (κ = 0).