V. V. Panasyuk

Paths of Edge Cracks in Rolling Bodies under the Conditions of Boundary Lubrication

We propose an analytical model for investigation of the processes of fracture of a near-surface layer of bodies in the case of their unidirectional rolling under conditions of limit lubrication. The step-by-step calculation of trajectories of propagation of fatigue cracks using the criteria of local fracture in a complicated stressed state and with regard for the specific features of loading in a contact cycle is a key element of the model. We investigate trajectories of propagation of an edge crack depending on the angle of its initial inclination to the boundary of the body, the friction coefficient between the contacting bodies, and the pressure of lubricant on the crack lips. The theoretical results confirm the experimental data and the known hypothesis of Way, according to which a lubricant plays the decisive role in the appearance of a pit.

Influence of the Stress-Strain State on the Distribution of Hydrogen Concentration in the Process Zone

We propose a theoretical-experimental approach to the determination of the concentration of hydrogen in the process zone. The plots of the dependences of the concentration of hydrogen on the mechanical characteristics of the material and external load are constructed.

Effect of Rounding the Edges in the Base of a Rider on the Stress Intensity Factors in a Body with Edge Cracks

We study the dependence of the stress intensity factors in a body containing an edge arbitrarily oriented crack on the radius R of rounding of the edges in the base of a rider pressed with unilateral friction to the damaged body near the crack mouth. Within the framework of the two-dimensional problem, this body is modeled by an elastic half plane with edge cut and the action of the rider is replaced by a load reproducing the distribution of pressure established by Aleksandrov and Romalis [Contact Problems in Machine Building, Mashinostroenie, Moscow, 1986] in the contact zone of two elastic cylinders with initial contact strip. The numerical results are obtained for the identical materials of contacting bodies for a half length of the initial contact zone b = [5; 10] mm, the following values of the radius: R = [0.1; 1.0; 10.0; 100.0] mm, and different inclination angles of the edge crack, relative positions of the rider and the crack, and crack lengths.

A METHOD FOR THE ASSESSMENT OF THE SERVICEABILITY AND FRACTURE HAZARD FOR STRUCTURAL ELEMENTS WITH CRACKLIKE DEFECTS

We propose a method for the assessment of strength and fracture hazard of defective structural elements based on the parameter of “crack-growth resistance structural elements,” which characterizes the rate of change in the stress intensity factor near the crack tip in the course of crack propagation in this structural element. We present examples of evaluation of the serviceability and durability of typical structural elements with cracklike defects of different shapes and locations under the action of quasistatic and cyclic loads.

STRESS CONCENTRATION NEAR SHARP AND ROUNDED V-NOTCHES

We present a survey of investigations of the stress concentration in elastic bodies weakened by sharp and rounded V-notches. Special attention is given to the unified approach to the study of stress distributions near the indicated stress concentrators in the case where the stress intensity factors at sharp tips of the notches are determined according to the stress concentration factors in the vicinity of a rounded notch with small radius of curvature. We consider two-dimensional bodies with internal acute-angled holes and edge V-notches.

Decohesive Concept of the Interaction of Hydrogen with Metals

We consider some concepts of the interaction of hydrogen with metals (iron and its alloys) under loads in hydrogen-containing media and, in particular, their hydrogen embrittlement. This problem is analyzed in numerous works, where different concepts and models are proposed for the substantiation of the mechanisms of hydrogen embrittlement of metals. However, these concepts do not enable us to understand the dual character of the action of hydrogen on the deformation of metals, i.e., the facilitation of their plastic deformation and embrittlement. We describe the decohesive concept of hydrogen–metal interaction based on which it is possible to explain the processes of plasticization of metals in the initial stage of deformation and their embrittlement in the course of subsequent deformation. We also present a survey of investigations in this direction carried out by researchers of the Karpenko Physicomechanical Institute of the Ukrainian National Academy of Sciences.

Evaluation of the Stress Concentration Near Thin Elastic and Viscoelastic Inclusions

We present a survey of the efficient approximate methods for the evaluation of the stress concentration near notches, slits, and cavities filled with elastic or viscoelastic materials. Our main attention is given to a method based on the use of solutions of the corresponding problems for bodies with mathematical cuts along the median surfaces of the concentrators. The idea of the method is to replace an inclusion with a certain volume by a surface with unknown discontinuities of stresses and/or displacements. We describe a procedure of construction of the integral equations of the corresponding boundary-value problems used to determine the indicated discontinuities. By an example of the inhomogeneities bounded by canonical surfaces, we illustrate the efficiency of construction of approximate solutions of these problems.

Methods for the Evaluation of the Contact Durability of Elements of the Tribojoints (A Survey)

We present a survey of the literature devoted to the models and methods aimed at the evaluation of the contact durability of elements of the tribojoints (in rolling and fretting couples) and analyze the results of investigations in the scientific directions regarded as basic for the proposed methods and including, in particular, the mechanics of fatigue fracture of cyclically contacting bodies and the contact problems of the mathematical theory of cracks. We consider the problems connected with the application of new approaches and the results of investigations of rolling contact fatigue and fretting fatigue to the prediction of the contact durability of elements of the tribojoints.

Nucleation and growth of corrosion-fatigue cracks from semicircular notches

The initial stages of corrosion fatigue on the surfaces of semicircular notches are studied for the system of low-strength carbon steel and a 3% NaCl solution under different loading and electrochemical conditions on the notch surface. It is shown that the process of electrochemical dissolution of the metal plays the predominant role in the first stages of growth of short corrosion-fatigue crack. We suggest an expression for the prediction of the characteristic density of corrosion-fatigue cracks as a function of the synergistic action of cyclic stresses and parameters of the process of electrochemical dissolution on the notch surface.