The limiting state of force systems and processes of damage of them. Report 1. Energy criteria of failure

A composite energy criterion of failure of a force system in relation to test temperature and level of normal and frictional stresses is proposed and a method has been developed for separation from the full mechanical and thermal energy of their effective portions expended on formation and accumulation of damages. The concept has been introduced of the parameters of interaction of different constituents of the effective energy and a method is given for evaluation of them. Particular criteria of thermal force failure have been obtained and understandings of the limits of (mechanical) destruction and of temperature destruction have been introduced. On the basis of experimental results satisfactory correspondence to the test data of the thermal force criterion in the 4 K to T _melt range has been established for nickel and aluminum and an analysis has also been made of the change in mechanisms of damage of these materials in connection with varying of the level of stresses and test temperature.Translated from Problemy Prochnosti, No. 1, pp. 11–23, January, 1993.     

Evaluation of the limiting state of defective drawing dies. Report 3. Analytical solution of the problem of the limiting state of a defective drawing die with a reinforcing ring

Strength of Materials -     

Analysis of relationships governing wear-fatigue damage. Report 2

The main results of investigations of direct (effect of the friction and wear processes on the variation of the fatigue resistance characteristics) and reversed (effect of cyclic stresses on intensification of wear) effects are presented. The diagram of limiting states of the force systems characterized by complex-wear-fatigue-damage is analyzed. The problems of calculating the strength and endurance of these systems are discussed. It is shown that, in particular, in contact-mechanical friction (CMF) and friction-mechanical fatigue (FMF) under specific conditions the force systems can operate reliably with a strength margin factor smaller than unity. An equation for calculating the endurance and FMF is derived.     

The structural-energy state of metal nanopowders and the problems of certifying them

The basic characteristics of metal nanopowders, namely, the shape, particle sizes, the metal component content, the chemical activity parameters, the electrochemical characteristics, and the thermodynamic state of the nanoparticles and nanopowders, are considered. Experimental results are presented on the use of standard methods of analysis and the features of their use when determining the above characteristics. It is shown that, for certifying nanopowders as metastable systems, a whole range of methods of analysis is required.     

Stress state and the static strength of mechanically inhomogenous welded joints. Report 2. Effect of a small degree of mechanical inhomogeneity on the strength of butt welded joints

The characteristics of the stress state in the presence of a small amount of mechanical inhomogeneity (k_u<2) have been uncovered for welded joints containing a soft interlayer. An approach has been developed for estimating the weight carrying ability of these joints. The association of the contact tangential stresses with the basic structural-geometric parameters of a welded joint (k_u, k) under conditions of plane strain has been established based on the mathematical theory of plasticity. More accurate formulas describing the stress tensor components and the mean stresses during ductile failure have been presented. These formula are in good agreement with the experimental data. In assuming an equilibrium distribution of the strength characteristics over the volume of the soft interlayer, expressions were obtained which can be used at the design stage for choosing the optimum parameters for the welded joint, thus increasing its reliability.Translated from Problemy Prochnosti, No. 4, pp. 35–38, April, 1991.     

The impact of high-risk drivers and benefits of limiting their driving degree of freedom

The perception of drivers regarding risk-taking behaviour is widely varied. High-risk drivers are the segment of drivers who are disproportionately represented in the majority of crashes. This study examines the typologies of drivers in risk-taking behaviour, the common high-risk driving errors (speeding, close following, abrupt lane-changing and impaired driving), their safety consequences and the technological (ITS) devices for their detection and correction. Limiting the driving degree of freedom of high-risk drivers is proposed and its benefits on safety as well as traffic operations are quantified using VISSIM microscopic traffic simulation at various proportions of high-risk drivers; namely, 4%, 8% and 12%. Assessment of the safety benefits was carried out by using the technique of simulated vehicle conflicts which was validated against historic crashes, and reduction in travel time was used to quantify the operational benefits. The findings imply that limiting the freedom of high-risk drivers resulted in a reduction of crashes by 12%, 21% and 27% in congested traffic conditions; 9%, 13% and 18% in lightly congested traffic conditions as well as 9%, 10% and 17% in non-congested traffic conditions for high-risk drivers in proportions of 4%, 8% and 12% respectively. Moreover, the surrogate safety measures indicated that there was a reduction in crash severity levels. The operational benefits amounted to savings of nearly 1% in travel time for all the proportions of high-risk drivers considered. The study concluded that limiting the freedom of high-risk drivers has safety and operational benefits; though there could be social, legal and institutional concerns for its practical implementation.     

Stress relaxation in zirconium carbide. Report 2. Mechanisms of stress relaxation. The relationship of the processes of creep and relaxation

Mechanisms of stress relaxation in ZrC_1.00 (d=6–35 .m) in the area of the ductile-to-brittle transition temperature (1600–2200C) are considered. It is established that in the 1800–2000C range for ZrC_1.00 with grain sizes of 6 and 14–35 m, respectively, stress relaxation occurs as the result of pure grain boundary slip while at higher temperatures by intragranular cross slip. It is shown that creep in the steady stage and stress relaxation in ZrC_1.00 with grain sizes of 6–35 m are controlled by different physical processes, which makes impossible obtaining for these materials of data on stress relaxation by conversion with use of information on steady creep.Translated from Problemy Prochnosti, No. 2, pp. 55–60, February, 1994.     

Numerical modeling of heat-transfer processes in the investigation of the state of thermal stress of tribotechnical systems

On the basis of an analysis of the electrothermomechanical processes occurring in rapid sliding of solids, the article suggests a mathematical model for investigating the thermal state of structural elements with a view to the physical peculiarities of their interaction. A combined numerical and analytical approach is used. The analytical method is used for a quantitative estimate of the dissipation of electromagnetic and mechanical energies into thermal energy, the numerical method is used for calculating the field characteristics of the thermal processes. A numerical analysis is made of the slider-type pair (Cu-Sn) with a straight guide with constant sliding speed of the moving element v = 7000 m/sec.Translated from Problemy Prochnosti, No. 11, pp. 50–57, November, 1993.     

Effect of an initial force in a rivet hole on the longevity of a structural component. Report 1. Analysis of the stressed state on the perimeter of the hole with allowance for the initial force

Kharkov Aviation Institute. Translated from Problemy Prochnosti, No. 1, pp. 93–97, January, 1988.     

Numerical investigations of the dynamic processes in vibroimpact systems in modeling impacts by a force of contact interaction

On the basis of the results of numerical analysis, it is shown that the introduction of a force of contact interaction varying according to the Hertz law to the equation of motion makes it possible to model impacts between colliding bodies both under harmonic and stochastic external loads. This enables us to deduce the law of motion of the bodies in a vibroimpact system for the entire time axis, including the period of impact. We perform the numerical optimization of the parameters of the vibroimpact system by the method of gradient projection with correction of the discrepancy in constraints. The comparative analysis of the efficiency of the dynamic nonimpact dampers and shock absorbers of vibrations is presented. Translated from Problemy Prochnosti, No. 6, pp. 82–90, November–December, 2008.