Issue 4
JTAM, Sofia, vol. 52 Issue 4 (2022)

PROF. DSC YACHKO IVANOV, MEMBER OF THE BULGARIAN ACADEMY OF SCIENCES, AND HIS REMARKABLE SCIENTIFIC CAREER

Ana Yanakieva, Robert Kazandjiev
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria


Academician Yachko Ivanov turned 90 in September 2022. We are pleased to present a short interview with the jubilee outlining the basic achievements of his remarkable scientific carrier.

JTAM, Sofia, vol. 52 Issue 4 pp. 297-304 (2022), [Full Article]

FREQUENCIES OF TRIANGULAR PLATE WITH TWO-DIMENSIONAL PARABOLIC THICKNESS UNDER TEMPERATURE FIELD

Nisha Dagar1, Reeta Bhardwaj1, Naveen Mani2, Kamal Kumar1, Sudeshna Ghosh1, Amit Sharma1, Lokesh Singh3
1Department of Mathematics, Amity University Haryana, Gurugram, India
2Department of Mathematics, Chandigarh University, Chandigarh, India
3Faculty of Engineering and Technology, Villa College, Maldives

The effect of two-dimensional parabolic thickness on frequencies of triangular plate (isosceles, right angled, and scalene triangle) is investigated for clamped edge condition under one dimensional temperature field. First three modes of vibration are computed on different variation of plate parameters using Rayleigh-Ritz method. The objective of this study is to illustrate a numerical data in the form of mode frequencies and showing how variation in mode frequencies can be control by choosing an appropriate variation in plate parameters. A comparative study of the frequencies with other available results is also shown here.

JTAM, Sofia, vol. 52 Issue 4 pp. 305-316 (2022), [Full Article]

HIGH LIFT CONTROL WITH A CFJ AROUND A NACA 4415 AIRFOIL

Zakaria Imine, Mahi Senouci, Sidi Mohamed Amine Meftah
Aeronautics and Propulsive Systems Laboratory. Faculté de Génie Mécanique Université des Sciences et de la Technologie D'Oran Mohamed BOUDIAF BP1505 El M'nouar Oran-31000, Algeria

An active concept of lift control around a NACA 4415 airfoil has been presented in this paper. On the upper surface, geometric modifications were implemented where the blowing and suction were localized relative to the leading edge. In order to validate the mathematical model, a baseline NACA 4415 airfoil was examined and compared with experimental data. Several numerical investigations were considered in which the blowing's localization and momentum coefficient were modified. These configurations were tested at a velocity of 21 meters per second with angles of attack ranging from 0 to 40 degrees. The CFD results show that the CFJ concept is quite promising, and that by pushing the stall to atypical angles of attack, it can offer a significant increase in lift force and a delay in boundary layer separation. However, several analytical correlations for predicting the coefficient of maximum lift as a function of the blowing position and the coefficient of momentum have been established.

JTAM, Sofia, vol. 52 Issue 4 pp. 317-334 (2022), [Full Article]

DYNAMIC NANO-CRACKS INTERACTION IN GRADED MAGNETOELECTROELASTIC SOLID

Tsviatko V. Rangelov, Yonko D. Stoynov, Petia S. Dineva
1Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
2Faculty of Applied Mathematics and Informatics, Technical University, Sofia 1000, Bulgaria
3Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria

Dynamic fracture behaviour of multiple anti-plane nano-cracks in infinite functionally graded magnetoelectroelastic (MEE) solid under excitation of time-harmonic SH-wave is studied. The applied approach is based on the non-hypersingular traction based boundary integral equation method (BIEM) for the graded bulk MEE solid extended with the non-classical boundary conditions and the localized constitutive law for the MEE matrix-nanocrack interface within the framework of the Gurtin-Murdoch theory. The formulation allows for an exponential variation of the material properties in an arbitrary direction. The boundary integral equation (BIE) system is treated by using the frequency dependent fundamental solution derived analytically by Fourier transforms. The numerical solution provides displacements and tractions at any point in the infinite graded solid as well as the generalized crack opening displacements from which the generalized stress concentrations are determined. Simulations for different nano-cracks configurations such as collinear, parallel or nanocracks in arbitrary position to each other are presented and discussed. They demonstrate among others the MEE coupling, the frequency dependent shielding and amplification effects resulting from nano-cracks interaction and reveal the sensitivity of the stress concentration factors to the complex influence of wave-crack and crack-crack interactions, existence of material gradient and surface elasticity effects.

JTAM, Sofia, vol. 52 Issue 4 pp. 335-350 (2022), [Full Article]

SAFETY ZONE WITHIN THE LOAD SPACE OF DIFFUSIVELY SURFACE-REINFORCED STRUCTURAL COMPONENTS

Ana Yanakieva, Anguel Baltov, Gergana Nikolova
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bontchev St., bl. 4, 1113 Sofia, Bulgaria

The paper proposes a new Methodology for determining the safety zone of a structural element in the load space. To calculate the load-bearing capacity of the selected composite structural element, the Approximate Computational Model (ACM) created by the authors is applied, adapted, and extended for strength load-bearing capacity. The structural element is reinforced on both sides with a reinforcing substance and subjected to overloads (loads above the permissible norms). Through appropriately selected dimensionless parameters, a load space is built, and boundary surfaces of load-bearing capacity are built in it. These surfaces enclose the required volume safety zone.

JTAM, Sofia, vol. 52 Issue 4 pp. 351-364 (2022), [Full Article]

INFLUENCE OF TYPE OF ADHESIVE ON THE INTERFACE DEBONDING OF A BaTiO3/EPOXY STRUCTURE UNDER TIME HARMONIC MECHANICAL LOAD AND ELECTRIC FIELD AT ENVIRONMENTAL CONDITIONS

Tatyana Petrova1, Elisaveta Kirilova1, Wilfried Becker2, Jordanka Ivanova3
1Bulgarian Academy of Sciences, Institute of Chemical Engineering, Acad. G. Bonchev Str., bl. 103, 1113 Sofia, Bulgaria
2Technical University of Darmstadt, Franziska-Braun-Straße 7, 64287 Darmstadt, Germany
3European Polytechnical University, 23 Sv. Sv. Kiril i Metodiy Str., 2300 Pernik, Bulgaria

The study deals with investigation of the effect of the used adhesive upon the interface delamination at adhesively bonded piezoelectric patch/layer structure BaTiO3/Epoxy subjected to time harmonic mechanical load and electric field at environmental conditions. This is needed for a prediction of conditions, at which these type of structures work safely (without failure). For the interface shear stress in the overlap zone of structure, at two different thicknesses of its adherends and three adhesives used, a solution method based on shear lag and Fourier method has been applied. The types of solutions obtained depend mainly on the adherends' thickness, the magnitude and frequency of the applied mechanical loading and the shear modulus of the used adhesive. Based on the analysis conducted it has been shown that with increasing magnitude and frequency of applied mechanical load, the delamination length also increased. The delamination could be avoided if the stronger adhesives and thicker adherends are chosen. The debond length is highly dependent on the magnitude of electric displacement. The analytical equation for resonant frequencies in the considered structure is developed on the base of obtained solutions and they are calculated at all three investigated adhesives.

JTAM, Sofia, vol. 52 Issue 4 pp. 365-380 (2022), [Full Article]

INVESTIGATION OF GLASSY CARBON COATING DEPOSITED ON TITANIUM ALLOY: MICROSTRUCTURE AND MECHANICAL PROPERTIES

Vladimir Petkov1, Mihaela Aleksandrova1, Veselin Petkov1, Dimitar Teodosiev2, Anna Bouzekova-Penkova2
1Bulgarian Academy of Sciences, Institute of Metal Science,\\ Equipment and Technology with Hydroaerodynamic Center, "Acad. Angel Balevski'', 67 "Shipchenski Prohod'' Blvd, 1574 Sofia, Bulgaria
2Bulgarian Academy of Sciences, Space Research and Technology Institute, 1. "Acad. Georgy Bonchev'', 1113 Sofia, Bulgaria

The deposition of glassy carbon coating on the widely applied in implantology titanium alloy – Ti 6V 4Al, is performed by a novel original thermo-chemical method, developed in the Bulgarian Academy of Sciences. The deposition of glassy carbon was carried out in a protective inert environment of argon at high temperature around 1000°C. The combination of biocompatible carbon containing coating and biocompatible titanium alloy represents an innovative implant material for medical use. An important aspect of the new material development process is the study of the mechanical properties and microstructure. Therefore, the microstructure and the mechanical characteristics of the obtained composite biocompatible material, consisting of titanium matrix and glassy carbon coating, were studied in the present work. The microstructure of the coating and its elemental composition were examined by metallographic microscope and by SEM-EDS analysis. Mechanical tests have also been performed in order to determine and compare the ultimate tensile strength and tensile yield strength of titanium alloy samples with and without glassy carbon cover. The hardness and the modulus of elasticity of the considered materials are determined by instrumented indentation technique.

JTAM, Sofia, vol. 52 Issue 4 pp. 381-392 (2022), [Full Article]