A. A. Lebedev

Determination of Damage Accumulated in Structural Materials by the Parameters of Scatter of Their Hardness Characteristics

The authors propose a method for estimating “degradation” of the structural state of materials due to damage accumulation during their operation. The scatter of hardness characteristics determined from the results of mass tests is taken as a damage parameter. The paper presents the findings of experimental studies of the scatter of hardness characteristics of materials after some operation time under cyclic, short- and long-term static loading conditions.

Monitoring of Current State of Pipe Metal in Active Gas Pipelines. Experimental Method and Results

Degradation of the structural state of pipe metal in gas pipelines upon long-term operation is assessed by the proposed hardness method. It is demonstrated that the method provides information needed for monitoring operational reliability of gas pipelines.

Systematic evaluation of the damage to a material during plastic deformation

Aluminum alloy D16 is used as an example to systematically evaluate the damage to metal on the basis of characteristics of its damping capacity (logarithmic vibration decrement), acoustic emission, and weight as determined by a new method developed by the authors. It is shown that the damage sustained by metallic materials during static loading can be estimated from the change in the vibration decrement and certain acoustic-emission parameters. These conclusions are substantiated by similar relations expressing the dependence of these parameters on the dilatation of the material in an evaluation of its volume change.

On the Choice of Stress Invariants in Solving Problems of Mechanics

It is proposed to formulate strength criteria as a relationship between the stress intensity and dimensionless invariant η, which is equal to the ratio of the first stress-tensor invariant to the stress intensity. The use of the η invariant in the case of plane stress is proved to be correct. A comparison of calculated and experimental data demonstrates advantages of the proposed formulation of the ultimate state conditions over the classical approach. Possible ways of how to extend the presented approach to a triaxial stress state are indicated.

Model of damage cumulation in metallic materials under static tension

The article deals with a new phenomenological model of damage cumulation in metallic materials subjected to static tension. The main parameter of the running state of the material, which is put in correspondence with the degree of loosening, is the Poisson ratio at the stage of loss of strength (the descending part of the stress-strain curve). The suggested model describes satisfactorily the results of specially arranged experiments.

Effect of stressed-state form on failure kinetics and crack resistance in martensitic-aging steel. 1. Study of the failure process stages

We investigate the kinetics of failure in martensitic-aging steel during the concluding stages of deformation in statically elongated smooth specimens and in specimens with stress concentrators. Particular attention is devoted to the unique features encountered in the formation and onset of a separating macrocrack in the specimens being tested. Initially, using the methods of detailed metallography, we reproduce the pattern of prefailure zone formation, the crack trajectories subsequently passing through these zones. We have noted common and distinguishing features in damage formation in the steel being tested, with consideration given to the form of the stressed state.

Fracture Mechanism in Plastic Sheet Materials

The method of complete stress–strain diagrams has been proved efficient for the assessment of a sheet materials resistance to macrocrack propagation in thin-wall structural elements and for the prediction of stresses that correspond to the growth onset of macrocracks of various lengths in wide plates by the results of testing small specimens.

Effect of the grain size on the accumulation of damage in a metal subjected to plastic deformation

The integrated assessment of the accumulation of damage in D16 aluminum alloy with coarse grains (≈3 and 8 mm) grown by a special thermal treatment shows that the grain size can strongly affect the rate of accumulation of damage in metallic materials under static loading. The degree of damage to the metal correlates well with some parameters of its damping ability and acoustic emission. These results are important from the scientific point of view and can be used for the solution of practical problems, in particular, for the improvement of existing methods and developing new methods and equipment for nondestructive testing of deformed metals.

EFFECT OF THE FORM OF STRESSED STATE ON THE KINETICS OF DAMAGE ACCUMULATION AND CRACK RESISTANCE OF BODY STEEL 15Kh2MFA UNDER DIFFERENT CONDITIONS. COMMUNICATION 1. STAGEWISE PROCESS OF STEEL KP60 FAILURE

The kinetics of body steel KP60 failure are studied in the final stages of deformation with static tension for smooth specimens and with stress concentrators. Attention is concentrated on features of the generation and start of separation macrocracks in test specimens. Common and distinctive features of damage formation in the test steel are noted taking account of the form of stressed state.

Effect of the type of stress state on the micromechanisms of failure of maraging steels during equilibrium deformation

Fractographic and microstructural results are presented on the equilibrium failure of samples made of maraging steel, including those carrying stress concentrators of various form. It has been shown that it is possible to trace the actual micromechanism of failure of ductile materials during the growth and development of microcracks in terms of the stress state.