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The effect of the magnetic field on the Rayleigh-Taylor instability in a couple-stress fluid

Chavaraddi K. B., Awati V. B., Nandeppanavar M. M., Gouder P. M.

International Journal of Applied Mechanics and Engineering

2018

Vol. 23, no. 3

611--622

In this study we examine the effect of the magnetic field parameter on the growth rate of the Rayleigh-Taylor instability (RTI) in a couple stress fluids. A simple theory based on fully developed flow approximations is used to derive the dispersion relation for the growth rate of the RTI. The general dispersion relation obtained using perturbation equations with appropriate boundary conditions will be reduced for the special cases of propagation and the condition of instability and stability will be obtained. In solving the problem of the R-T instability the appropriate boundary conditions will be applied. The couple-stress parameter is found to be stabilizing and the influence of the various parameters involved in the problem on the interface stability is thoroughly analyzed. The new results will be obtained by plotting the curves between the dimensionless growth rate and the dimensionless wave number for various physical parameters involved in the problem (viz. the magnetic field, couple-stress, porosity, etc.) in the problem. It is found that the magnetic field and couple-stress have a stabilization effect whereas the buoyancy force (surface tension) has a destabilization effect on the RT instability in the presence of porous media.

Mode I and mode II fatigue crack growth resistance characteristics of high tempered 65G steel

Lenkovskiy T. M., Kulyk V. V., Duriagina Z. A., Kovalchuk R. A., Topilnytskyy V. H., Vira V. V., Tepla T. L.

Archives of Materials Science and Engineering

2017

Vol. 84, nr 1

34--41

Purpose: To investigate the fatigue crack growth at normal tension and transverse shear of 65G steel with the high tempered martensite microstructure and to build an appropriate fatigue crack growth rate curves. To determine the main and auxiliary fatigue crack growth resistance characteristics, which are necessary for machine parts life-time estimation at rolling contact fatigue conditions. Design/methodology/approach: For determination of fatigue crack growth resistance at normal tension a standard compact specimens with edge crack were tested using a hydraulic testing machine and fatigue testing at transverse shear were performed on the I-beam specimens with the edge longitudinal crack using the original testing setup. For crack growth measurement an optical cathetometer B-630 was used. The crack growth rate V was calculated as crack length increment during loading cycles. The stress intensity factor range K was determined by dependence "K = (1 – R)Kmax accordingly to the standard test methods. To establish crack faces friction factor at transverse shear fragments of fractured beam specimen containing crack faces were cut out and tested as a friction pair according to Amontons Coulomb's law. On the base of test results the fatigue crack growth rate curves in logarithmic coordinates "K vs. V were built. These graphical dependencies for normal tension and transverse shear were used for determination of fatigue crack growth resistance characteristics: fatigue threshold "Kth, fracture toughness "Kfc, "K1-2 and "K2-3 which indicates the beginning and the end of middle-amplitude region of curve, "K*, parameters C and n of Paris’s equation. Metallographic and fractographic analyses were performed on the scanning electronic microscope Zeiss EVO 40XVP. Findings: Empirical dependences of the stress intensity factor range on fatigue crack growth rate at normal tension and transverse shear of 65G steel with the high tempered martensite microstructure are obtained. Based on these graphical dependencies the fatigue thresholds and fracture toughness as well as the parameters of Paris’s equation are determined. Research limitations/implications: The fatigue crack growth on 65G steel under low-, medium- and high-amplitude cyclic loading at normal tension and transverse shear was investigated. The fatigue crack growth rate values for a wide range of stress intensity factor are estimated. On the base of fractographical analysis the features of fracture of high tempered martensite in 65G steel at transverse shear are studied. It is shown that the transverse shear crack faces friction factor for high tempered martensite structure is less than for low tempered martensite. Practical implications: Using the fatigue crack growth resistance characteristics of 65G steel at normal tension and transverse shear and related fatigue crack growth rate curves it is possible to predict the life-time of machine parts made of steels with high tempered martensite structure, working at rolling contact fatigue conditions. Originality/value: Complete fatigue crack growth rate curves of 65G steel with tempered martensite structure at normal tension and transverse shear are built and the fatigue crack growth resistance characteristics for both modes of fracture are determined for the first time.

Kinetyka wzrostu warstw w procesie RFCVD

Jonas S., Jaglarz J., Kyzioł K., Januś M., Murawska E.

Inżynieria Materiałowa

2014

Vol. 35, nr 6

492--495

gazowej (CVD) zależy od wielu parametrów, takich jak temperatura podłoża, stężenie, szybkość przepływu reagentów chemicznych, ciśnienie, moc generatora plazmy (w przypadku metod PACVD) oraz czas osadzania. Mimo wielu prac związanych z otrzymywaniem warstw w procesie CVD w literaturze brak jest danych dotyczących badań wpływu ostatniego z wymienionych parametrów, czasu osadzania, na szybkość i mechanizm ich wzrostu. Praca zawiera wyniki badań szybkości wzrostu warstw azotku krzemu i warstw węglowych dotowanych azotem na podłożu (001) Si w funkcji czasu osadzania w procesie chemicznego osadzania z fazy gazowej wspomaganego plazmą generowaną przez fale o częstotliwości radiowej RFCVD (13,56 MHz, 400 W). Na podstawie pomiarów grubości warstw stwierdzono, że krzywe kinetyczne nie mają charakteru liniowego, lecz składają się z etapów, które systematycznie powtarzają się i charakteryzują się na początku szybszym tempem wzrostu, a następnie spowolnieniem pod koniec każdego z etapów. Dane te wskazują, że proces wzrostu w tym układzie jest limitowany liczbą aktywnych miejsc na powierzchni podłoża, a w dalszych etapach na powierzchni tworzących się warstw. Przeprowadzono dyskusję nad prawdopodobnym mechanizmem na podstawie teorii stanu przejściowego.

Layer growth rate in chemical processes of chemical deposition from gaseous phase (CVD) depends on several parameters, such as substrat temperature, concentration and flow velocity of reacting substances, pressure, plasma generator power (in case of PACVD method) and deposition time. Independently on numerous studies on the problem in question, there are no literature data concerning the influence of the deposition time and layer growth mechanism. The results of examination on growth rate of silicon nitride layers and nitrogen-doped carbon layers substrate (001) Si in function of deposition time in the process of plasma-assisted chemical vapour deposition RFCVD (13.56 MHz, 400 W), have been described in the present study. On the basis of the layer thickness measurements it was proved that kinetic curves have nonlinear character but they comprise several stages, which are systematically repeated. It was also proved that the mentioned curves are characterized with bigger growing rate at the beginning and then the rate is moderated at the end of each stage. The data indicate that the growth process within this system is limited by number of active centers on the substrat surface, and in next stages on the surface of growing layers. Discussion on probable mechanism with respect to theory of transitional state has also been presented.