Global Approach of Tribomechanical Development of Hybrid Aluminium Matrix Syntactic Foams

Hybrid syntactic foams with AlSi12 aluminium matrix were produced by pressure infiltration. The volume ratio of iron to ceramic hollow sphere reinforcement (in the same size range) was varied, and hybrid syntactic foams were also produced with bimodal size ceramic reinforcement. Previously, a very detailed analysis of the mechanical properties of the composites was made with quasi-static compression tests, and their tribological properties were investigated by pin-on-disc method in dry and lubricated conditions. The present article establishes and clarifies the correlations between mechanical and tribological properties. The coefficient of friction, height loss of the specimens and specific wear showed good correlation with different mechanical parameters, e.g. density, structural stiffness and yield strength. The established trends and correlations between mechanical and tribological behaviour enable a better understanding of materials design and selection for further applications of mechanically loaded sliding machine parts.     

Friction and Thermal Effects of Engineering Plastics Sliding Against Steel and DLN-Coated Counterfaces

Polymers are increasingly used in tribological applications, because of their self-lubricating ability, corrosion resistance and chemical compatibility. However, their performance depends strongly on the parameters of the total tribological system. Not only polymer characteristics, but also counterface properties become important because of their influence on friction and wear, on surface energy and on the thermal conductivity of the total system. Applying a Diamond-Like Nanocomposite (DLN) coating on a steel counterface can improve the tribological behaviour of the sliding couple under certain conditions. In the case of metal sliding against DLN, the high hardness and the wear resistance of the coating is advantageous for better tribological properties. However, for polymers sliding against DLN, the lower thermal conductivity of the DLN coating compared with a steel mating surface dominates friction and wear. In case of polyamides this results in worse tribological performance in contact with the DLN coating, because of polymer melting. In the case of more rigid polymers, such as, e.g., POM-H and PETP, lower coefficients of friction lead to lower frictional heat generation. In these cases, the thermal characteristics of the counterface are less important and the lower surface energy of the DLN coating is favourable for decreased adhesion between the polymer and the coating and consequently better tribological properties.     

Transient processes during synchronization of coupled bistable oscillators with chaotic dynamics

Transient processes in a chain of nonidentical Chua oscillators resistively coupled via nonlinear elements admitting cubic approximation have been numerically simulated in cases of mutual and unidirectional coupling. It is demonstrated that the transient processes during both mutual and induced (unidirectional) chaotic synchronization are enhanced with increasing detuning between the oscillatory circuits of partial subsystems and suppressed with increasing coefficient of coupling. The time of establishment of a synchronous operation regime in the case of mutual coupling is, under otherwise identical conditions, shorter than in the case of unidirectional coupling. The dependence of the duration of establishment of a synchronous operation regime on the moment of coupling switch-on is considered.     

Converting harmonic oscillations into chaos

A new simple model of a system with chaotic dynamics, based on the equations of bistable systems, is considered. The possibility of converting harmonic signals into chaotic oscillations, which represent intermittent irregular and switching quasi-regular motions, is demonstrated by numerical methods. The mechanism of chaotization is analyzed using the results of numerical calculations.     

Controlled oscillations in chain of unidirectionally coupled bistable oscillators with chaotic dynamics

Equations of a chain of n (n = 1, 2, ...) unidirectionally coupled bistable oscillators possessing chaotic dynamics are presented. Numerical analysis has been performed for a system of three identical autooscillatory systems with nonlinear elements admitting cubic approximation. It is shown that, as the degree of coupling between units in the chain increases, their motions in the phase space become more complicated and even chaotization of oscillations may take place at the parameters with which separate oscillators exhibit regular motions in the autonomous regimes. The features of the influence of a driving oscillator on the motions of a driven bistable subsystem are related to filtration of the driving signal in the circuit of the driven subsystem.     

A controllable chaotic system based on inductively coupled bistable oscillators

A mathematical model of a new controllable autooscilatory chaotic system based on inductively coupled Chua’s oscillators is described. Numerical simulations show that, using a chaotizing feedback algorithm, chaotic oscillations in this system can be excited in regimes where only regular oscillations are generated otherwise.     

Influence of lead on the wear resistance of cast composites of the Fe-Cr-Cu-Ti-C system in sliding friction

The positive influence of lead (2.5%) on the original structure of a cast composite of the Fe-Cr-Cu-C-Ti system, its wear rate, friction coefficient, and the formation of secondary structures is established under the conditions of dry friction and friction with boundary lubrication. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 73–80, November–December, 2006.     

Gas-chromatographic study on the stereoselectivity of deprenyl metabolism

The metabolism and urinary elimination of both (-)-deprenyl and (+)-deprenyl have been studied. Gas-chromatographic analysis with mass specific detection indicated that the metabolism of (-)-deprenyl results in a large excess of methamphetamine compared to amphetamine, while the metabolism of (+)-deprenyl gave nearly equal amounts of amphetamine and methamphetamine. A novel deprenyl metabolite, phenylacetone, was also identified in our studies.     

Chaotization of oscillations in a nonatonomous rigidly excitable system with time delay

An external harmonic drive signal is used for stimulating chaos in a system with time delay, in which the parameters admit only rigid excitation of oscillations and a single impact produces only regular motions. The results of numerical simulations are presented and the mechanism of chaos induction is considered.