Issue 2

JTAM, Sofia, vol. 47 Issue 2 (2017)

Regular Mechanical Transformation of Rotations into Translations: Part 1. Kinematic Analysis and Definition of the Basic Characteristics

Emilia Abadjieva1, Valentin Abadjiev2
1Graduate School of Engineering and Resource Science, Faculty of Engineering and Resource Science, Akita University, Tegatagakuen-machi 1-1, Akita, Japan
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 4, 1113 Sofia, Bulgaria

The science that study the processes of motions transformation upon a preliminary defined law between non-coplanar axes (in general case) axes of rotations or axis of rotation and direction of rectilinear translation by three-link mechanisms, equipped with high kinematic joints, can be treated as an independent branch of Applied Mechanics. It deals with mechanical behaviour of these multibody systems in relation to the kinematic and geometric characteristics of the elements of the high kinematic joints, which form them. The object of study here is the process of regular transformation of rotation into translation. The developed mathematical model is subjected to the defined task for studying the sliding velocity vector function at the contact point from the surfaces elements of arbitrary high kinematic joints. The main kinematic characteristics of the studied type motions transformation (kinematic cylinders on level, kinematic relative helices (helical conoids) and kinematic pitch configurations) are defined on the bases of the realized analysis. These features expand the theoretical knowledge, which is the objective of the gearing theory. They also complement the system of kinematic and geometric primitives, that form the mathematical model for synthesis of spatial rack mechanisms.

JTAM, Sofia, vol. 47 Issue 2 pp. 03-23 (2017), [Full Article]

Mathematical Modeling of Thermofrictional Milling Process Using ANSYS WB Software

K. T. Sherov1, M. R. Sikhimbayev2, A. K. Sherov1, B. S. Donenbayev1, A. K. Rakishev1, A. B. Mazdubai1, M. M. Musayev1, A. M. Abeuova1
1Karaganda State Technical University, 56 B. Mira St., 100027 Karaganda, Kazakhstan
2Karaganda Economic University, 9 Akademicheskaya St., 100009 Karaganda, Kazakhstan

This article presents ANSYS WB-based mathematical modelling of the thermofrictional milling process, which allowed studying the dynamics of thermal and physical processes occurring during the processing. The technique used also allows determination of the optimal cutting conditions of thermofrictional milling for processing various materials, in particular steel 40CN2MA, 30CGSA, 45, 3sp. In our study, from among a number of existing models of cutting fracture, we chose the criterion first proposed by prof. V. L. Kolmogorov. In order to increase the calculations performance, a mathematical model was proposed, that used only two objects: a parallelepiped-shaped workpiece and a cutting insert in the form of a pentagonal prism. In addition, the work takes into account the friction coefficient between a cutting insert and a workpiece taken equal to 0.4 mm. To determine the temperature in the subcontact layer of the workpiece, we introduced the coordinates of nine characteristic points with the same interval in the local coordinate system. As a result, the temperature values were obtained for different materials at the studied points during the cutter speed change. The research results showed the possibility of controlling thermal processes during processing by choosing the optimum cutting modes.

JTAM, Sofia, vol. 47 Issue 2 pp. 24-33 (2017), [Full Article]

Influence of Poroelasticity on the 3D Seismic Response of Complex Geological Media

Frank Wuttke1, Petia Dineva2, Ioanna-Kleoniki Fontara3
1Institute of Applied Geoscience, Kiel University, Germany
2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria
3Institute of Civil Engineering, Technical University of Berlin, Germany

Elastic wave propagation in 3D poroelastic geological media with localized heterogeneities, such as an elastic inclusion and a canyon is investigated to visualize the modification of local site responses under consideration of water saturated geomaterial. The extended computational environment herein developed is a direct Boundary Integral Equation Method (BIEM), based on the frequency-dependent fundamental solution of the governing equation in poro-visco elastodynamics. Bardet’s model is introduced in the analysis as the computationally efficient viscoelastic isomorphism to Biot’s equations of dynamic poroelasticity, thus replacing the two-phase material by a complex valued single-phase one. The potential of Bardet’s analogue is illustrated for low frequency vibrations and all simulation results demonstrate the dependency of wave field developed along the free surface on the properties of the soil material.

JTAM, Sofia, vol. 47 Issue 2 pp. 34-60 (2017), [Full Article]

Theoretical Exploration of Exponential Heat Source and Thermal Stratification Effects on the Motion of 3-Dimensional Flow of Casson Fluid over a Low Heat Energy Surface at Initial Unsteady Stage

N. Sandeep1, I. L. Animasaun2
1Department of Mathematics, VIT University, Vellore-632014, India
2Department of Mathematical Sciences, Federal University of Technology, Akure, Ondo State, Nigeria

Within the last few decades, experts and scientists dealing with the flow of non-Newtonian fluids (most especially Casson fluid) have confirmed the existence of such flow on a stretchable surface with low heat energy (i.e. absolute zero of temperature). This article presents the motion of a three-dimensional of such fluid. Influence of uniform space dependent internal heat source on the intermolecular forces holding the molecules of Casson fluid is investigated. It is assumed that the stagnation flow was induced by an external force (pressure gradient) together with impulsive. Based on these assumptions, variable thermophysical properties are most suitable; hence modified kinematic viscosity model is presented. The system of governing equations of 3-dimensional unsteady Casson fluid was non-dimensionalized using suitable similarity transformation which unravels the behavior of the flow at full fledge short period. The numerical solution of the corresponding boundary value problem (ODE) was obtained using Runge-Kutta fourth order along with shooting technique. The intermolecular forces holding the molecules of Casson fluid flow in both horizontal directions when magnitude of velocity ratio parameters are greater than unity breaks continuously with an increase in Casson parameter and this leads to an increase in velocity profiles in both directions.

JTAM, Sofia, vol. 47 Issue 2 pp. 61-82 (2017), [Full Article]

Influence of Interface Gap on the Stress Behaviour of Smart Single Lap Joints Under Time Harmonic Load

Jordanka Ivanova, Varbinka Valeva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 4, 1113 Sofia, Bulgaria

Adhesive joints are frequently used in different composite structures due to their improved mechanical performance and better understanding of the failure mechanics. The application of such structures can be seen in aerospace and high technology components. The authors developed and applied modified shear lag analysis to investigate the hygrothermalpiezoelectric response of a smart single lap joint at environmental conditions (with/without an interface gap along the overlap zone) and under dynamic time harmonic mechanical and electric loads. The main key is the study of the appearance of possible delamination along the interface. As illustrative examples, the analytical closed form solution of the structure shear and the axial stresses response, as well as the interface debond length, including influence of mechanical, piezoelectric, thermal characteristics and frequencies is performed and discussed. All results are presented in figures. The comparison of the shear stress and electric fields for both cases of overlap zone (continuous or with a gap) is also shown in figures and discussed.

JTAM, Sofia, vol. 47 Issue 2 pp. 83-99 (2017), [Full Article]