Issue 1
JTAM, Sofia, vol. 49 Issue 1 (2019)

IMPLEMENTATION OF THE AXIOMS OF COSSERAT–ZHILIN SYSTEMS ON EXAMPLES OF THEIR MAIN TYPES

Al. Cheremensky
Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria


The differential equations of motion are derived for different types of Cosserat–Zhilin systems in the case where Stocks theorem is applicable. There are defined multiplicative groups which represent the measure of stress as a (well-defined) linear isotropic map of {strain} tensor or tensor of {strain velocities} for classical and polar continua in 2- and 3-dimensional cases.

JTAM, Sofia, vol. 49 Issue 1 pp. 003-019 (2019), [Full Article]

THE INFLUENCE OF THE PIEZOELECTRIC EFFECT ON THE ANALYSIS OF ELASTIC STRESSES FOR A COMPOSITE DISK UNDER THE PARABOLIC DISTRIBUTION OF TEMPERATURE

Berrabah Hamza Madjid
Laboratoire Matériaux et Hydrologie, Centre Universitaire Ahmed Zabana Relizane, Relizane, 48000, Algérie

In this paper, we studied the influence of the piezoelectric effect under the variation of the parabolic temperature, for this purpose, a thermo-elastic composite disk reinforced by steel fibers is used for the analysis of the radial and tangential elastic thermal stresses. The solutions of the stresses were obtained analytically. In addition, a comparison between these expressions for different temperature values is calculated.

JTAM, Sofia, vol. 49 Issue 1 pp. 020-027 (2019), [Full Article]

THE CONDITIONS OF CONJUGATION IN THE TASKS OF MOISTURE TRANSFER ON A THIN CLAY INCLUSION TAKING INTO ACCOUNT SALT SALUTIONS AND TEMPERATURE

Yurii Chui, Petro Martyniuk, Mykola Kuzlo, Oksana Ulianchuk-Martyniuk
National University of Water and Environmental Engineering, Rivne, Ukraine

The processes of non-isothermal moisture transfer of single-component chemical solutions in the porous environment containing thin semi-permeable clay inclusions have been considered. The conjugation conditions for the functions of humidity, salt concentration and temperature have been modified. The modification has been based on taking into account the dependences of the parameters of the porous medium on the physico-chemical processes and osmotic flows.

JTAM, Sofia, vol. 49 Issue 1 pp. 028-038 (2019), [Full Article]

A MODIFIED METHOD FOR MODELLING OF SPREAD FOOTING UNDER UNIFORM DISTRIBUTED LOAD USING WINKLER'S MODEL

Peyman Mianji, Ehsan Seyedi Hosseininia
Department of Civil Engineering, Ferdowsi University of Mashhad, Azadi Sq., Mashhad, Iran

Recent developments and advancements in soil models and computer programs failed to prevent structural engineering to use one the most elementary theories in modeling of the soil-structure interaction, i.e. Winkler's model. Superseding the soil with all its complexity with a series of uncoupled, independent springs whose stiffness known as the modulus of subgrade reaction (Ks), imposes many non-avoidable errors to the model. In the first two parts of the paper, the impact of soil-foundation system stiffness on the Ks distribution alongside the precision of the theoretical relations for Ks estimation are investigated as the basis for the proposed dividing technique presented in the rest of the article.

JTAM, Sofia, vol. 49 Issue 1 pp. 039-050 (2019), [Full Article]

EXPERIMENTAL DAMAGE IDENTIFICATION BY APPLYING STRUCTURAL DYNAMIC MODEL UPDATING

Shankar Sehgal, Harmesh Kumar
Mechanical Engineering, UIET, Panjab University, Chandigarh, 160014 India

In this paper, structural dynamic model updating has been utilized in experimentally evaluating the extent of damage at six locations of a damaged cantilever beam structure. Six elements of the beam had lateral cuts. These cuts resulted in unknown reductions in flexural rigidity parameters. These parameters were taken as updating parameters and the reductions in these parameters were identified through dynamic model updating and evaluated to be 54.49, 100.09, 79.63, 82.17, 45.60 and 27.40 Nm2. Updated finite element model of the structure was created by incorporating reduced flexural rigidity parameters. Dynamic results of updated model showed that total absolute error in prediction of natural frequencies was reduced by 98.36%, which confirmed accurate identification of flexural rigidity parameters and hence damage extents in the beam.

JTAM, Sofia, vol. 49 Issue 1 pp. 051-061 (2019), [Full Article]

EVALUATION OF THE LAME'S CONSTANTS IN THEORY OF ELASTICITY BY ULTRASONIC MEASURMENTS

Alexander Popov1, Georgy Dobrev2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113, Sofia, Bulgaria
2Institute of Metal Science, Equipment and Technologies, Bulgarian Academy of Sciences, Shipchenski prohod St. 67, 1574, Sofia, Bulgaria

The evaluation of Lame's constants (λ μ) is taken in theory of elasticity. An interest in practice is the possibility of non-destructive evaluation (NDE) of (λ μ) by measuring ultrasound wave propagation longitudinal and transversal velocities (VL VT) with unilateral access to the test sample.

JTAM, Sofia, vol. 49 Issue 1 pp. 062-070 (2019), [Full Article]

ESHELBY'S INCLUSION AND SCREW DISLOCATION PROBLEMS FOR A THREE-PHASE PIEZOELECTRIC LAMINATE

Xu Wang1, Peter Schiavone2
1School of Mechanical and Power Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
2Department of Mechanical Engineering, University of Alberta, 10-203 Donadeo Innovation Centre for Engineering, Edmonton, Alberta, T6G 1H9, Canada

We propose a simple yet effective method based essentially on analytic continuation to derive analytical solutions for a screw dislocation or a two-dimensional Eshelby inclusion of arbitrary shape in a three-phase piezoelectric laminate composed of two semi-infinite piezoelectric media bonded together via an intermediate piezoelectric layer of finite thickness. The screw dislocation or the Eshelby inclusion can be located either in the upper semi-infinite piezoelectric medium or in the intermediate piezoelectric layer. Elegant expressions for the image force acting on the piezoelectric screw dislocation are presented and compared with existing results. We also observe some very interesting properties of the solutions obtained.

JTAM, Sofia, vol. 49 Issue 1 pp. 071-082 (2019), [Full Article]

SURFACE ROUGHNESS ESTIMATION OF DENTAL MATERIALS USING SPECKLE CONTRAST

Simeon Karpuzov1, Gergo Mitov2, Assen Shulev1
1Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
2Steiner LandstraЯe 124 A-3500, Krems-Stein, Austria

In this paper a simple technique for surface roughness estimation of composite dental material samples widely used in modern stomatology is presented. The proposed method is easily applicable and based on statistical properties of diffusely scattered laser light. The main challenge we addressed was the specific structural and optical properties, as well as the complex geometric shapes of real dental restorations. A relation between surface roughness and speckle contrast, used in the presented method, is verified.

JTAM, Sofia, vol. 49 Issue 1 pp. 083-093 (2019), [Full Article]

AUTOMATIC BONE DRILLING IN HIP FRACTURES OSTEOSYNTHESIS

Tony Boiadjiev1, George Boiadjiev2, Kamen Delchev3, Ivan Chavdarov4, Rumen Kastelov5
1Institute of Information and Communication Technologies, Bulgarian Academy of Sciences, Sofia, 1113, Bulgaria
2Mathematics and Informatics, Sofia University, Sofia, 1164, Bulgaria
3Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, 1113, Bulgaria
4Institute of System Engineering and Robotics, Bulgarian Academy of Sciences, Sofia, 1113, Bulgaria
5Orthopaedic and Trauma Clinical Centre of Ministry of Interior, Sofia, 1606, Bulgaria

This paper presents an investigation of automatic bone drilling application in osteosynthesis of hip fractures. The real hip fractures osteosynthesis includes bone drilling from hip femur through the neck (along its axis) and the hip head to its far cortex avoiding joint penetration by hip head far cortex registration. The automatic execution of such a task by the Orthopedic bone Drilling Robot "ODRO" is the main contribution of this paper. A femoral head cortex registration algorithm is proposed for automatic drilling the proximal femur (hip joint). Experiments are provided and graphs illustrating the results are presented and commented to validate them.

JTAM, Sofia, vol. 49 Issue 1 pp. 094-104 (2019), [Full Article]