Journal of Theoretical and Applied Mechanics, Sofia, vol. 49 Issue 3 (2019)

Table of contents



WAVE SCATTERING AND STRESS CONCENTRATION IN A MAGNETO-ELECTRO-ELASTIC PLANE WITH A NANO-CRACK BY BOUNDARY INTEGRAL EQUATIONS

Yonko Stoynov1, Petia Dineva2, Tsviatko Rangelov3
1Faculty of Applied Mathematics and Informatics, Technical University, Sofia 1000, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
3Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria


Anti-plane elastodynamic problem for shear (SH) wave scattering and diffraction by a nano-crack in a magnetoelectroelastic (MEE) plane is solved herein. The presence of a nano-fracture within the MEE matrix gives rise to both wave scattering and stress concentration phenomena, the latter being responsible for fracture of the magnetoelectroelastic solid. The proposed model takes into consideration the surface/interface properties, the size of the nano-crack and the interaction between the crack, incident wave and the multifunctional MEE matrix. The method of solution is the boundary integral equation method (BIEM), which is first verified against benchmark examples and subsequently applied for numerical simulations. The BIEM formulation combines classical elastodynamic theory for the bulk solid with non-classical boundary conditions and the localized constitutive law for the matrix/nano-crack interface within the framework of the Gurtin-Murdoch theory. Also, frequency-dependent fundamental solution obtained via Radon transform for the equation of motion in the bulk MEE solid and it's derivatives are used as kernels in boundary integral equation (BIE). Results drawn from the numerical simulations reveal the degree of dependence of the dynamic stress concentration field (SCF) on the size of the nano-crack, surface and bulk material properties, coupled nature of the magnetoeletroelasticity, properties of the incident wave as frequency, wave length and wave propagation direction, dynamic interaction between the nano-crack, incident wave and coupled MEE continuum. The obtained results have applications in material science, computational fracture mechanics and nondestructive testing evaluation of multifunctional active nano-composites.

JTAM, Sofia, vol. 49 Issue 3 pp. 203-223 (2019), [Full Article]




CLASSICAL FEATURES OF THE MOTION OF A HEAVY BEAD SLIDING ON A ROTATING WIRE

Ata Abu-As'ad1, Hussein Shanak2, Jihad Asad2
1Dept. of Applied Mathematics, College of Science, Palestine Technical University, P.O. Box 7, Tulkarm, Palestine
2Dept. of Physics, College of Science, Palestine Technical University, P.O. Box 7, Tulkarm, Palestine


In this paper, we study the motion of a heavy bead sliding on a rotating wire. Our first step was constructing the classical Lagrangian of the system. Secondly, we derived the Euler-Lagrange equation (ELE). Thirdly, we solve the obtained ELE, which is a non-homogenous second order linear differential equation. Finally, by using MATLAB the equation is solved numerically for some selected parameters, and for specified initial conditions.

JTAM, Sofia, vol. 49 Issue 3 pp. 224-232 (2019), [Full Article]




A STUDY ON THE THREE-PHASE SEPARATOR MACHINE (TRICANTER) FOR OLIVE OIL EXTRACTION

Ashkan Shokrian1, Hossein Mobli2, Abbas Akbarnia3, Ali Jafari2, Hossein Mousazade2, Baoshan Zhu4
1College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran
2College of Agriculture & Natural Resources, University of Tehran, Tehran, Iran
3Iranian Research Organization for Science and Technology, Karaj, Iran
4Department of Energy and Power Engineering, Tsinghua University, Beijing, China


The present study is a simulation by using Computational Fluid Dynamics (CFD) technique for the multiphase complex fluid flow motion in a centrifugal separate machine (tricanter). The CFD model uses Volume of Fluid multiphase model coupled with Reynolds Stress turbulence model for two-phase flow predictions. This centrifugal device is designed for separated three-phase flow, two- phase liquid (water and olive oil) and one phase solid materials (olive pomace). The contours of pressure, velocity and volume fraction of each phase were obtained by CFD simulation. The results showed that the centrifuge machine is designed well to separate three different phases.

JTAM, Sofia, vol. 49 Issue 3 pp. 233-240 (2019), [Full Article]




MECHANICAL AND THERMAL PROPERTIES OF PLA BASED NANOCOMPOSITES WITH GRAPHENE AND CARBON NANOTUBES

Polya Angelova
Institute of Mechanics (OLEM), Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 4, Sofia, Bulgaria


This work investigates thermal and mechanical properties of poly(lactic) acid (PLA) based composites with 6wt.% graphene nanoplates (GNP) and multiwalled carbon nanotubes (MWCNTs), produced by melt extrusion. The crystallization increases, from amorphous for the PLA (∼ 9%) to semicrystalline (∼ 18%) for all nanocomposites with adding only 6% of filler compared with the pure polymer. Dynamic mechanical measurements in torsion show that in temperatures lower than Tg (from -20 to 60°C), when the material is in a solid state, the addition of a nanofiller, such as 6% graphene, results in an increase in storage modulus G' and loss modulus G'', which confirms the reinforcement effect of the nanofillers. We compare our material with the only one commercial benchmark filament Black Magic for 3D printing application with 14 wt.% graphene and carbon nanotubes.

JTAM, Sofia, vol. 49 Issue 3 pp. 241-256 (2019), [Full Article]




DEFORMATION CHECKS IN BASIC LINKS OF BIG CIRCULAR SAW MACHINES

Boycho Marinov
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 4, Sofia, Bulgaria


In this article, deformation checks in basic links of big circular saw machines have been made. For this purpose, the maximum deflections in the most endangered cross sections of the main shaft are calculated. The biggest values are compared with the admissible values for the respective material. The normal operation of the big circular saw machine is guaranteed if the actual values of the deflections are equal or less than the admissible values. In this work, solutions for all cross sections of the main shaft are proposed. These solutions make it possible to carry out deformation checks when designing new circular saw machines.

JTAM, Sofia, vol. 49 Issue 3 pp. 257-272 (2019), [Full Article]




AN APPROACH TO ASSESS THE IMPACT OF EXTREME EXTERNAL INFLUENCES ON THE FUNCTIONALITY OF SPECIALIZED DEVICES

Nikolay L. Georgiev
Institute of Metal Science, Equipment and Technologies with Hydro- and Aerodynamics Centre ``Acad. A. Balevski'', Bulgarian Academy of Sciences, 67, Shipchenski prohod St., 1574 Sofia, Bulgaria


The presented study proposes an approach to accelerate the tests intended to assess the impact of extreme external influences on the functionality of specialized devices. For this purpose, models are proposed for describing the probability of failure-free operation of specialized devices in areas close to the limit values of the external effects parameters for which they are designed. Examples are given for applying the approach to assess the impact of extreme external temperature and mechanical impacts.

JTAM, Sofia, vol. 49 Issue 3 pp. 273-284 (2019), [Full Article]




OPTIMIZATION OF THE SWINGING MODE OF THE BOOM CRANE UPON A COMPLEX INTEGRAL CRITERION

Viatcheslav Loveikin, Yuriy Romasevych, Ivan Kadykalo, Anastasia Liashko
Department of Machines and Equipment Design, National University of Life and Environmental Sciences of Ukraine, Kyiv, 03041, Ukraine


The article presents the method of solving the problem of elimination of load oscillations on a flexible suspension during the swing of a boom crane with simultaneous minimization of dynamic forces in the transmission mechanism. A complex integral dynamic criterion to minimize includes the root-mean-square value of an elastic torque in the drive mechanism and the rate of its changing. The solution of the optimization problem is represented in the discrete form. The multi-epoch particle swarm optimization (ME-PSO) method has been used for that purpose. It helped to obtain the discrete values of the kinematic, force and power characteristics of the boom system. The resultant optimal mode of the boom-system swing has improved crane performance in terms of reliability and energy efficiency.

JTAM, Sofia, vol. 49 Issue 3 pp. 285-296 (2019), [Full Article]