Issue 1

JTAM, Sofia, vol. 39 Issue 1 (2009)

Investigation of Boron Products Used in Brake Pads

Ibrahim Mutlu
Afyon Kocatepe University, Technical Education Faculty, ANS Campus, Afyonkarahisar, Turkey

Recently, different brake pads have started to be investigated in brake friction industry by replacing the asbestos with new materials. In this study, boron products were used as a new material in brake pads. Specifically, refined Boric Acid (BA) and Borax (Anhydrous) (BX) with raw Ulexite (U) and Colemanite (C) were used. Different amounts of boron products were used in the mix of other regular ingredients in brake pad. Newly formulated brake pad material with eight different ingredients has been tested under Friction Assessment and Screening Test (FAST). Friction coefficient, wear rate, and Scanning Electron Microscope (SEM) for friction surfaces were examined to assess the performance of these samples.

JTAM, Sofia, vol. 39 Issue 1 pp. 01 (2009)

Integral Stability in Terms of Two Measures for Impulsive Differential Equations

S. G. Hristova
Department of Applied Mathematics and modelling, Plovdiv University, 4000 Plovdiv, Bulgaria

This paper investigates integral stability in terms of two measures of systems of nonlinear impulsive differential equations. Piecewise continuous Lyapunov functions have been applied. The obtained sufficient conditions significantly depend on the impulses.

JTAM, Sofia, vol. 39 Issue 1 pp. 02 (2009)

Long-Wavelength Monotonic Marangoni Instability in a Binary Mixture Layer with Nonlinear Soret Effect

P. Kalitzova –Kurteva1, S. Slavtchev1, A. Oron2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 4, 1113 Sofia, Bulgaria
2Department of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel

The appearance of mass flux in binary mixtures, due to temperature gradient, is known as thermodiffusion or Soret effect. In addition to the classical diffusive flux, the total mass flux also consists of a thermodiffusive flux initiated by the gradient. The Soret effect is called nonlinear when the thermodiffusive flux is a product of the temperature gradient and a linear function of the solute concentration in the mixture. The nonlinear Soret effect is pronounced mostly in very dilute solutions. The paper is devoted to the problem of Marangoni instability in a thin horizontal layer of a binary liquid mixture in the presence of the nonlinear Soret effect. The layer is bounded by a rigid plate from below and a gas-liquid non-deformable interface from above. It is subjected to a perpendicular temperature gradient. The case of heating from below is only considered. Based on the linear stability analysis, criteria for the onset of monotonic Marangoni instability with respect to long-wavelength perturbations are obtained in the case of small Biot numbers.

JTAM, Sofia, vol. 39 Issue 1 pp. 03 (2009)

Rotating Hydromagnetic Optically-Thin Gray Gas Flow with Thermal Radiation Effects

S. K. Ghosh1, O. Anwar Bég2, J. Zueco3
1Department of Mathematics, Narajole Raj College, P.O.-Narajole, Dist.- Midnapore (West), 721 211, West Bengal, India
2Mechanical Engineering Department, Sheffield Hallam University, Sheaf Building, Sheffield, S1 1WB, UK
3Thermal Engineering and Fluids Department, Technical University of Cartagena, Campus Muralla del Mar, Cartagena, 30202, Spain

Exact solutions are presented for the steady magnetohydrodynamic (MHD) rotating viscous convective flow with thermal radiation and induced pressure gradient for a fluent regime which is optically-thin i.e. an optically finite gray gas which does not re-absorb radiation emitted from other parts of the gas. The conservation equations for momentum and energy are non-dimensionalized and solved using the Laplace Transform Method, a technique which has been rigorously employed and validated in numerous previous communications by the authors. The effects of magnetic field parameter (i.e. Hartmann number squared, M2), rotational parameter (i.e. the inverse Ekman number, K2), Grashof number (i.e. free convection parameter, GrM/sub>) and radiation-conduction parameter (K1) on the primary (u) and secondary velocity (w) distributions are computed and described in detail. Both primary and secondary velocities are found to increase with increasing K1. Increasing GrM/sub> reduces considerably both primary velocity (u) and secondary velocity (w), with flow reversal present. Increasing K2 reduces primary velocity but increases secondary velocity closer to the plate surface. Increasing M2 reduces u and v values. Primary and secondary shear stresses are also computed. The model finds applications in astrophysical flows and MHD energy systems.

JTAM, Sofia, vol. 39 Issue 1 pp. 04 (2009)

Experimental and Modeling Study of the Temperature Effect on the Creep of a Composite Material

A. Kouadri-Boudjelthia1, M. Elmeguenni1, A. Imad1, A. Bouabdallah, M. Tahar Abbes
1Laboratory of Mechanics of Lille, CNRS UMR 8107, Ecole Polytech’Lille, University of Lille1, Cité Scientifique, Av. Paul Langevin, 59655 Villeneuve d’Ascq, France
2Faculty of Physics, USTHB of Bab Ezzouar ALGIERS, Algeria
3Department of Mechanical, University Hassiba Benbouali of CHLEF, Algeria

This study shows the temperature effects on the creep parameters of a composite material made out of non saturated polyester and reinforced with randomly oriented glass fibres type C with a density of 450 g/m2. This material works in a medium presenting a large variation in temperature. To better illustrate the complexity of the creep phenomenon and show its dependence on temperature, load, fibre concentration and cristallinity rate, an experimental and numerical simulation behaviour study was carried under several different temperatures and three levels of loading out to determine the evolution of the law in function of the relevant parameters. The creep behaviour was then modelled by using a phenomenological relationship defined as ε = ε0 + B σmtk, where ε, ε0 and σ are, respectively, creep in tension after time t, the instantaneous strain, and the pressure applied on the tube over time t. Several samples were tested under varying temperatures and load changes. This paper presents a method to the phenomenological study of primary and secondary creep based on the experimental results and modelling by an empirical approach. Model the tertiary creep behaviour also based on the experimental results by the viscoelastic rheological model of Eyring. The experimental data was then used to determine the phenomenological relationship and its appointed coefficients ε, ε0, σ.

JTAM, Sofia, vol. 39 Issue 1 pp. 05 (2009)