BULGARIAN ACADEMY OF SCIENCES NATIONAL COMMITTEE OF THEORETICAL AND APPLIED MECHANICS Journal of Theoretical and Applied Mechanics
Print ISSN: 0861-6663 Online ISSN: 1314-8710
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Journal of Theoretical and Applied Mechanics, Sofia, vol. 54 Issue 2 (2024)
Table of contents
István Ecsedi, Attila Baksa
Institute of Applied Mechanics, University of Miskolc, H-3515 Miskolc, Miskolc-Egyetemváros, Hungary
Studying inhomogeneous structural elements is a very important task. Many studies deal with inhomogeneity of the type whose introduction into an originally homogeneous body does not change its physical fields belonging to the prescribed boundary conditions. This type of inhomogeneity is called neutral inhomogeneity. In the relevant literature, we find several examples of this, mainly in the mathematical theory of elasticity. A prime example is the Saint-Venant’s torsion problem of prismatic bars. In the present paper a steady-state heat conduction problem is considered in a two-dimensional square-body. The Cartesian orthotropic solid square body consists of a circular inclusion. The circular inclusion is placed at the center of the square and it has two parts, a core and a coating component, both of which are cylindrically orthotropic. The paper deals with the determination of the thermal conductance of component bodies such that the temperature distribution in originally homogeneous Cartesian orthotropic solid square body does not change. All results of the paper is based on the Fourier’s theory of heat conduction in solid body.
JTAM, Sofia, vol. 54 Issue 2 pp. 135-146 (2024), [Full Article]
Dessislava Pashkouleva1, Miglena Kirilova-Doneva1,2
1Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
2Faculty of Pharmacy, Medical University-Sofia, Sofia 1000, Bulgaria
The repair of the abdominal wall defects with surgical
meshes is a universally procedure worldwide. This paper aims to investigate
the influence of aging on the mechanical properties of three types of meshes
made of polypropylene, like basic material and different additional
materials. Quasi-static tensile test was performed on samples of baseline
meshes and simulated aging samples. Our results showed that all basic meshes
were orthotropic and presented different mechanical behaviour. It is not
possible to conclude that one of the meshes has better properties than the
others. The main observation was that when the meshes were exposed to aging,
all investigated mechanical parameters decreased or increased in both
directions according to different compositions and architectures of meshes.
The changes in mechanical properties over time necessitate the creation of a
guide for surgeons including results obtained after mechanical experiments.
They can use it to choose the proper mesh according to type of hernia, age
and condition of the patient.
JTAM, Sofia, vol. 54 Issue 2 pp. 147-158 (2024), [Full Article]
Mariya L. Antonova, Andreyan G. Georgiev, Tsvetalin T. Totev
Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria
The viscoelasticity of blood vessels determines their biomechanical
behavior. The present work aims to develop and validate a new device
modification for the forced oscillation method and to elaborate an
experimental protocol for investigating the direct effect of opioids on the
arterial wall~\textit{in vitro}~in a prolonged experiment. The construction and software of a
previously constructed device were improved and upgraded. A new photo optic
recording system and Analog-To-Discrete conversion and recording scheme were
developed. The elaborated experimental protocol allows an accumulative
treatment with opioids while keeping the preparation vital. The total error
of the measurement modules is less than 4.45%. The device ensures
sufficient repeatability and precision in recording the response
oscillations and estimating the viscoelastic characteristics of biological
tissues.
JTAM, Sofia, vol. 54 Issue 2 pp. 159-171 (2024), [Full Article]
Georgi Stoilov, Dessislava Pashkouleva, Vassil Kavardzhikov
Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
Digital image correlation is a mathematical technique which can be
used successfully for evaluation displacements and deformations of large
engineering components. Compared to traditional contact measurements,
digital image correlation allows full-field deformation information to be
obtained by non-contact procedure. Herein, we propose a method to improve
the accuracy in evaluation of two dimensional displacement fields by
introducing markers, which are used during the following digital image
correlation analysis. The effectiveness of the proposed method is
illustrated in processing of displacement fields on the surface of a wooden
wall, subjected to cyclic loading. The results are in good agreement (less
than 1%) with the data obtained by linear voltage differential
transformer sensors. Experiments show that the use of markers is a
perspective way to improve the accuracy of a digital image correlation
method, and to improve its applicability in structural monitoring.
JTAM, Sofia, vol. 54 Issue 2 pp. 172-185 (2024), [Full Article]
Sonia Parvanova1, Petia Dineva2
1Department of Structural Engineering, University of Architecture, Civil Engineering and Geodesy, Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria
Elastic time-harmonic and transient wave
scattering by multiple anisotropic nanoiclusions is the object of this
study. The nanoinclusions are situated in an infinite anisotropic medium under plane strain
conditions. The model is in the frame of surface elasticity theory proposed
by Gurtin-Murdoch in 1975. The computational tool is a combination of the boundary
integral equations method (BIEM) based on the frequency dependent
elastodynamic fundamental solution for anisotropic continua, Gurtin-Murdoch
theory, and Fourier integral transforms. Stress concentration factors and
scattered wave displacements for nanoinclusions swept by pressure or shear
waves are computed. The benchmark cases used for verification of the
developed numerical scheme, illustrate the accuracy of the present
methodology. Finally, in the companion paper (Part II), the detailed parametric
study is presented and discussed.
JTAM, Sofia, vol. 54 Issue 2 pp. 186-200 (2024), [Full Article]
Sonia Parvanova1, Petia Dineva2
1Department of Structural Engineering, University of Architecture, Civil Engineering and Geodesy, Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria
The mechanical model describing wave scattering by a
system of elastic anisotropic nanoinclusions situated in an elastic
anisotropic plane subjected to incident plane wave were considered in the
first part of this work. The model is in the frame of 2D elastodynamics for
general anisotropic continuum and surface elasticity theory proposed by
Gurtin and Murdoch in 1975. The aim of the current part is to illustrate that the
scattered wave field and stress concentration zones in an elastic generally
anisotropic nanoheterogeneous plane is a complex result of mutual play of
different key factors such as type and characteristics of the incident wave,
surface elasticity properties, material anisotropy and dynamic interactions
between nanoinclusions and between them and incident wave.
JTAM, Sofia, vol. 54 Issue 2 pp. 201-215 (2024), [Full Article]
Ahmed Allem, Mokadem Salem, Abderahmane Sahli, Sofiane Talbi
LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, BP 89, City Ben Mhidi, Sidi Bel Abbes 22000, Algeria
The aim of this work is to investigate the repair performance of
aircraft structures modeled by 2024-T3 aluminum plate with inclined central
cracks under biaxial complex loading. The mixed-mode stress intensity factor
(SIF) is greatly affected by biaxial loading. The goal is to reduce the
(SIF) level near the crack after repairing, and determine the best
orientation of patch fibers regarding the complex load. The results of the
study show that the fiber orientation should conform to the patch sequence
for better fixation efficiency.
JTAM, Sofia, vol. 54 Issue 2 pp. 216-231 (2024), [Full Article]
Trinh Dong Tinh
Hanoi University of Science and Technology, Hanoi, Vietnam
This paper presents research on the single scissor lift about two
problems: the influence of the mounting position of the hydraulic cylinder
on its required actuation force and evaluating the suitability of the
selected cylinder length to meet the required lifting height of the load.
The results show that when the cylinder is mounted at an inadequate place,
the lift cannot reach the require working height. Moreover, the mounting
position of the cylinder has a significant effect on the required actuating
force of the hydraulic cylinder: this required force varies in a wide range
from 4.1 to 11.8 times of the total load acting on the platform, depends on
the different mounting positions.
JTAM, Sofia, vol. 54 Issue 2 pp. 232-241 (2024), [Full Article]
Denys Storozhyk1, Anatolii Protasov1, Yurii Kuts1, Oleksandr Muraviov1, Iuliia Lysenko1, Yordan Mirchev2
1National Technical University of Ukraine, Igor Sikorsky Kyiv Polytechnic Institute, Kyiv, Ukraine
2Institute of Mechanics at the Bulgarian Academy of Sciences, Sofia, Bulgaria
The article is devoted to the study of the efficiency of using the
image fusion method for data augmentation when training neural networks for
thermal non-destructive testing. Using the example of training 75 neural
networks with the AlexNet architecture, the dependence of image
classification accuracy on the data augmentation method was analyzed. The
effectiveness of generating artificial images using the method of data
integration based on wavelet transformation was examined. The results of the
analysis demonstrate the advantages of using image fusion as a method of
data augmentation and enrichment to improve the efficiency of neural
networks. The superiority of the data augmentation method based on image
fusion using wavelet transform is proven.
JTAM, Sofia, vol. 54 Issue 2 pp. 242-252 (2024), [Full Article]