Journal of Theoretical and Applied Mechanics
Volume 39, Number 3, 2009
Evtim V. Zahariev
Acad.
e-mail: evtimvz@bas.bg
Juana M. Mayo
Department of Mechanical and Materials Engineering,
Camino de los Descubrimientos s/n, 41092
e-mail: juana@us.es
SPATIAL FRICTIONAL IMPACT OF RIGID AND FLEXIBLE MULTIBODY SYSTEMS
Abstract. In the paper the graphical methods
of Routh’s and Impulse Momentum Equations (IME) are presented. A novel
iterative methodology for solution of spatial frictional impact of multibody
systems is proposed. The iterative procedure consists in descretization of the
normal velocity and consequential computation of IME. At every iteration the
tangential velocity is pre-calculated analyzing the condition for sliding and
sticking. Examples of spatial frictional impact are presented. The sliding
trace is computationally derived. The paper will be of use for lecturers and
scientists dealing with the problems of frictional contact and impact and
presents short but the major references of the scientific investigations in the
field.
Key
words: impact, friction, multibody systems.
Ilker Sugozu
e-mail: ilkersugozu@hotmail.com
Ibrahim Mutlu
e-mail: ibrahimmutlu@hotmail.com
INVESTIGATION
OF THE EFFECT OF WASTE TIRE RUBBER ON FRICTION BEHAVIOUR IN AUTOMOTIVE BRAKE
LININGS
Abstract. Brake pads of automotive are composite
materials composed of more than ten different ingredients. Asbestos has been
used as a friction material but it has been prohibited to use in brake pad due to
its harmful effect on human health.
Therefore, new material investigation to replace the asbestos gained
acceleration.
In this study, Waste Tire Rubber
(WTR) was used as a new friction material in brake pads. Newly formulated brake
lining material with five different ingredients has been produced by using WTR.
WTR is used in different amount in the
mix of other regular ingredients in brake pad. Conventional techniques
have been used in the production of brake lining. In the experimental studies, the change of friction coefficient, the
temperature of friction surface and amount of wear were measured. In addition,
micro-structural characterizations of braking pads are carried out by using
Scanning Electron Microscopy (SEM). The strategy proposed in this paper
can be considered as an alternative to revalorize this kind of waste products. As a result, WTR can be used as friction materials in the
brake pads.
Key Words: brake pad, composite materials, friction, wear, Waste Tire Rubber (WTR).
Nikolay
K. Vitanov
Acad.
email: vitanov@imbm.bas.bg
Optimum
theory of turbulence: Ideas, methods and results
abstract. It is not possible to obtain closed mathematical expressions for the
complex velocity, temperature and other fields describing the turbulent motion
of the fluids. Instead of this we must use direct numerical simulations or
other methods to obtain analytical results for the flow quantities. There are
few such methods. One of them is the optimum theory of turbulence. This theory
leads to upper bounds on energy dissipation, transport of momentum, heat
transport, etc. The bounds are obtained by solution of the Euler - Lagrange
equations of variational problems formulated on the basis of the systems of
model equations.
Two
methods of the optimum theory of turbulence are widely used. The Howard-Busse
method is based on modelling of the flow fields by coupled modes with different
wave numbers (multi-α-solutions). The Doering - Constantin method is based
on a decomposition of the flow fields on background field which satisfies the
boundary condition and fluctuation field which satisfies zero boundary
conditions. The Doering - Constaintin method does not lead to better bounds but
it is more flexible with respect to
the
boundary conditions.
In
this paper we discuss the main ideas, the areas of application, and selected
upper bounds obtained by the optimum theory of turbulence. The two methods are
illustrated by their application to different fluid systems. The Howard - Busse
method is applied for obtaining of upper bounds on the
thermal
convection in a fluid saturated porous layer. The Doering – Constantin method
is applied for obtaining upper bounds on the energy dissipation of Couette - Ekman
flow.
Key words: fluid dynamics, turbulence, variational problems,
upper bounds, optimum theory of turbulence, Howard - Busse method, Doering -
Constantin method.
S. Slavtchev, P. Kalitzova –Kurteva,
Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria,
e-mails: slavcho@imbm.bas.bg, penka@imbm.bas.bg
A. Oron
Department of Mechanical Engineering,
Technion-Israel Institute of Technology,
e-mail: meroron@tx.technion.ac.il
LONG-WAVELENGTH OSCILLATORY MARANGONI INSTABILITY IN A BINARY MIXTURE
LAYER WITH NONLINEAR SORET EFFECT
Abstract. The emergence of a mass flux in
binary mixtures, due to temperature gradient, is known as thermodiffusion or
Soret effect. When the latter is present, in addition to the classical
diffusive flux, the total mass flux also contains a thermodiffusive flux.
Thermodiffusion is usually small, but it can be important in various separation
processes. The Soret effect is called nonlinear when the thermodiffusive flux
is proportional to a nonlinear function of the solute concentration in the
mixture. The nonlinear Soret effect is significant in very dilute solutions.
Recently, taking into account this effect, the long-wavelength monotonic Marangoni instability in a
thin horizontal layer of a binary liquid mixture heated from below was studied
by the present authors [1]. Here, the study is completed by considering the
case of oscillatory Marangoni
convection.
Key words: binary mixture, nonlinear Soret
effect, Marangoni oscillatory instability, long waves.
Valentin Velev, Todor
Dimov
e-mails: v.velev@shu-bg.net, dimov@shu-bg.net
Anton Popov
"Prof. Dr.
Assen Zlatarov" - Bourgas, 8000
e-mail: apopov1948@abv.bg
Christo Betchev
University of Chemical Technology and Metallurgy, 1756
e-mail:
bechev@lbchemicals.com
Deformation behaviour of
amorphous uniaxially oriented polyester samples caused by simultaneous thermal
and mechanical treatments
Key words: poly(ethylene terephthalate), amorphous filaments, linear heating,
strain stress, deformation behaviour, birefringence.
Richard Berenyi
3, Goldmann, H-1111
Mechanical Study of a
Micro-Machined Flexible Substrate
Abstract. A new
Three-Dimensional (3D) laser micromachining method of 3D flexible structures has been
introduced to enhance the current micromachining technology. The machining is
carried out with a simple Two-Dimensional (2D) movement of the laser beam on
the work piece. This method can be applied for machining 3D geometries or bending
edges in various materials. The purpose is to extract the material by an
ablation of matter in order to achieve “V” shape for multi-bend structure. The
process is well controlled and only selective polyimide material removing on bending edges was used. Two-layered polyimide-copper assembly was considered. This
is a practical case for multilayer structures such as layered composites and
coatings. The mechanical bending analysis of the system with residual stress
was carried out with
Key words: micro-machining, 3D package, laser processing, laser
ablation of polyimide, mechanical structures in polyimide, reliability test.