Journal of Theoretical and Applied Mechanics

Volume 36, Number 4, 2006

Contents

 

D. Maga, J. Halgos, D. Lahucky

 

Alexander Dubcek University of Trencin,

1, Studentska, 911 50 Trencin, Slovakia,

e-mail: maga@tnuni.sk

 

Finite Element based Analysis of Special Mechatronic Actuator

 

Abstract. The presented paper deals with computer based model of mechatronic actuator – high torque low speed step motor. The paper presents especially the possible ways of torque computation and their accuracy. This actuator has been designed and constructed according to the special demands – extremely low speed and high static torque. Since the speed can be controlled by actuator construction, the torque depends on a lot of additional parameters and can be influenced by e.g. current supply size and case, tooth and slot sizes etc. One of the most important knowledge, suitable for a lot of authors solving similar problems, is the choice of proper torque computation method with required accuracy of obtained results.

 

Key words: finite elements, electromechanical actuator, torque computation.

 

Penka G. Kalitzova-Kurteva, Slavtcho G. Slavtchev

 

Institute of Mechanics, Bulgarian Academy of Sciences,

Acad. G. Bonchev Str., Bl. 4, Sofia 1113, Bulgaria,

e-mail: penka@imbm.bas.bg, slavcho@imbm.bas.bg

 

Maria-Alcina Mendes

 

Department of Chemical Engineering and Chemical Technology,

Imperial College, London SW7 2AZ, UK,

e-mail: a.mendes@imperial.ac.uk

 

MARANGONI INSTABILITY OF LIQUID-LIQUID SYSTEMS WITH A SURFACE-TENSION-INCREASING SOLUTE

 

Abstract. The onset of Marangoni instability in partially miscible liquid-liquid systems, such as organic-aqueous systems, in the presence of surface-active solutes that increase the interfacial tension is studied. The organic phase is initially pre-saturated with water and diffuses in the aqueous phase after both phases are contacted. The aqueous phase is contaminated with a surface-active solute, which is also soluble in the organic liquid and is transferred across the interface between the liquids. Marangoni instability in such systems may be induced by interfacial tension gradients, due to the heat of solution released or absorbed on the interface and to the solute activity. A linear stability analysis is carried out for both cases of stationary and oscillatory perturbations. The compatible equations derived previously by the authors for arbitrary solute are analysed numerically in the case of surface-tension-increasing solutes.

It is shown that the necessary conditions for marginal instability depend considerably on the solute diffusivity ratio, the kinematic viscous ratio and the sign of the product of the heat of solution and the thermal interfacial tension coefficient.

 

Key words: partially miscible liquid-liquid systems, surface-tension-increasing solutes, mass and heat transfer, Marangoni instability.

 

J. Ivanova, V. Valeva

 

Institute of Mechanics, Bulgarian Academy of Sciences,

Akad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,

e-mail: ivanova@imbm.bas.bg, valeva@imbm.bas.bg

 

Z. Mroz

 

Institute of Fundamental Technological Research, PAS,

21, Swietokrzyska Str., 00-49 Warsaw, Poland,

e-mail: zmroz@ippt.gov.pl

 

MECHANICAL MODELLING OF THE DELAMINATION OF BI-MATERIAL PLATE STRUCTURE

 

Abstract. A bi-material structure consisting of two elastic isotropic plates bonded together by an interface under tension loading is studied. The case for one plate with a crack normal to the interface is considered. The interface is assumed to exhibit brittle failure at the critical shear stress value in a cohesive zone preceding debonding. Using modified Shear Lag model, the analytical solution is provided specifying the length of debonding and ultimate failure. The critical length of a partial debonding along the interface strongly depends on the elastic moduli and the geometry of the bi-material structure. The results are illustrated in figures and discussed.

 

Key words: elastic plate structure, normal crack, interface, delamination (debonding), constitutive models: elastic-brittle, elastic-softening (cohesive), elastic-slip, elastic-slip-softening, length of debonding.

 

Stoyan Stoytchev, Ljuben Hadjikov

 

Institute of Mechanics, Bulgarian Academy of Sciences,

Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,

e-mail: Stoyan@imbm.bas.bg

 

Viacheslav I. Egorov,

 

Volynskaya Hospital,

10, Starovolynskaya Str., 121352 Moscow, Russia

 

Andrey O. Baranov, Robert A. Turusov

 

Institute of Chemical Physics, Russian Academy of Sciences,

4, Kosygin Str., 117977 Moscow, Russia,

e-mail: rob-turusov@yandex.ru

 

Ilia V. Schastlivtsev

 

1st Surgical Department, Russian State Medical University,

ZIL Hospital, 26, Bakinskaya Str., Moscow, Russia

 

Passive visco-elastic mechanical properties of small human intestine. Comparative study with other soft tissues

 

Abstract. The transport function of the intestinal system is to a large extent mechanical. The intestinal wall is stretched passively and this passive deformation predisposes the consequent active contractions, peristaltic and bolus transport. Thus, the passive constitutive equations of the intestinal wall are of great importance in understanding the physiological function of the gastrointestinal tract. We investigated experimentally the visco-elastic properties of the specimens taken from the jejunum site of the human small intestine. The main hypothesis of the work is that they obey the quasi-linear visco-elastic theory, proposed by Fung. The analytical expression for the elastic response function was sought as an exponential function of the stretch ratio. The results show that the small intestine tissue manifests orthotropic mechanical behaviour, being much more deformable in the circumferential direction than in the longitudinal one. The analysis of the stress relaxation data suggests that the relaxation spectrum for the small human intestine is broader than for the elements of the cardio-vascular system and for articular cartilage, but it is shorter compared to papillary muscles and canine ligament. Therefore, we conclude that the relaxation behaviour of the small human intestine is similar to other soft biological tissues and can be adequately described by Fung’s theory. At the same time, the incorporation of strain rate effects into Fung’s theory gives unsatisfactory results for strain rates up to 0.3 %/s.

 

Key words: human intestine, soft biological tissues, stress-strain relation, stress relaxation, quasi-linear theory.

 

G. Nikolova, J. Ivanova

 

Institute of Mechanics, Bulgarian Academy of Sciences,

Acad. G. Bonchev Str. Bl.4, 1113 Sofia, Bulgaria,

e-mail: gery@mech.bas.bg, ivanova@imbm.bas.bg,

 

Z. Mroz

 

Institute of Fundamental Technological Research,

21, Swietokrzyska Str., 00-049 Warsaw, Poland,

e-mail: zmroz@ippt.gov.pl

 

Modelling of thermally induced progressive delamination in a two-plate structure

 

Abstract. A bi-material element composed of two elastic plates bonded together by an interface and subjected to monotonically increasing temperature is considered. The interface is assumed to exhibit brittle failure at the critical shear stress value or progressive damage in a cohesive zone preceding delamination. Two cases are considered, namely, uniform bonded plates and the case for one plate with a crack normal to the interface. The analytical solution qualitatively shows delamination and ultimate failure. The critical temperature values for both cases at full debonding are obtained and discussed.

 

Key words: elastic plates, monotonic thermal loading, delamination (debonding), transverse crack, constitutive models: elastic-brittle, elastic-softening (cohesive), elastic-slip and elastic-slip-softening, limit value of temperature.