Issue 2
JTAM, Sofia, vol. 54 Issue 2 (2024)

A STEADY-STATE HEAT CONDUCTION PROBLEM IN A COMPOSITE SOLID SQUARE TWO-DIMENSIONAL BODY

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]

EXPERIMENTAL INVESTIGATION OF LONG-TERM MECHANICAL RESPONSE OF SURGICAL MESHES

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]

A DEVICE FOR IMPLEMENTATION OF THE FORCED OSCILLATION METHOD ON STRIP PREPARATIONS OF BIOLOGICAL TISSUES IN VITRO IN PROLONGED EXPERIMENTS

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]

OFF-AXIS 2D DISPLACEMENT FIELDS EVALUATION BY DIGITAL IMAGE CORRELATION USING MARKERS

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]

WAVE SCATTERING BY NANOINLCUSIONS IN ANISOTROPIC PLANE. PART I: MECHANICAL MODEL

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]

WAVE SCATTERING BY NANOINLCUSIONS IN ANISOTROPIC PLANE. PART II: NUMERICAL RESULTS

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]

FRACTURE ANALYSIS OF REPAIRING CRACKED AIRCRAFT STRUCTURE

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]

INFLUENCE OF MOUNTING POSITION OF HYDRAULIC CYLINDER IN SCISSOR LIFT ON ITS WORKING PERFORMANCE

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]

ENHANCING NEURAL NETWORK EFFICIENCY IN AUTOMATED IMAGE ANALYSIS FOR THERMAL NONDESTRUCTIVE TESTING

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]