Journal of Theoretical and Applied Mechanics, Sofia, vol. 50 Issue 1 (2020)

Table of contents



50th ANNIVERSARY OF THE JOURNAL OF THEORETICAL AND APPLIED MECHANICS

Editorial Board


JTAM, Sofia, vol. 50 Issue 1 pp. 001-002 (2020), [Full Article]




STUDY ON THE DYNAMIC CONSTITUTIVE RELATION OF AZ31B MAGNESIUM ALLOY BASED ON JOHNSON–COOK MODEL

Guanghan Zhang1,2, Zhiwu Zhu1,2, Shoune Xiao1, Tao Zhu1, Qijun Xie2
1State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
2Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu Sichuan 610031, China


To study the mechanical behavior and constitutive model of a AZ31B magnesium alloy at a high strain rate, the dynamic response of a strain rate ranging from 1630 to 3544 s-1 to the AZ31B magnesium alloy was studied by conducting a split Hopkinson pressure bar experiment. The dynamic stress-strain behavior of the AZ31B magnesium alloy at a high strain rate was analyzed. The results showed that the AZ31B magnesium alloy undergoes a change from an isotropic hardening to a strain softening effect, and no strain rate effect is apparent. In addition, an improved Johnson–Cook constitutive model is employed to consider the influence of damage on the material and determine the parameters for the model. The improved Johnson–Cook model combined with the damage failure model can demonstrate the isotropic hardening behavior of the AZ31B magnesium alloy and the strain softening behavior caused by the damage. The fitting result was determined to be good as compared with the experimental results.

JTAM, Sofia, vol. 50 Issue 1 pp. 003-019 (2020), [Full Article]




EXPERIMENTAL INVESTIGATIONS OF DYNAMIC PERFORMANCE OF POLYPROPYLENE BALL BEARINGS

Nesrine Gaaliche1,2, Subramanian Chithambaram3, Raouf Fathallah1,4
1Unit of Mechanical Production Engineering and Materials, National School of Engineers of Sfax, University of Sfax, Soukra Road Km 4 BP. 1173-3038, Tunisia
2Department of Mechanical Engineering, University of Bahrain, P.O. Box 32038, Sakheer, Kingdom of Bahrain
3Department of Mechanical Engineering, School of Engineering, Bahrain Polytechnic, PO Box 33349, Isa Town, Kingdom of Bahrain
4National Engineering School of Sousse, University of Sousse, BP 264 Sousse Erriadh 4023, Tunisia


Thermoplastic bearings are finding its practical importance in light duty applications due to their good tribological property. Investigating the dynamic performance of thermoplastic bearing is crucial due to the heterogeneous material structure. In this work, effort has been made to investigate the dynamic performance of healthy and faulty polypropylene bearings. Condition monitoring of bearings is carried out using the developed test rig. The influence of the size of the defect, effect of frequency and load are investigated using vibration analysis. Radial accelerations and velocities were measured by accelerometers under different loads and frequencies. Test results reveal that FFT spectrum allows to localize the defect in the outer or the inner race and to characterize the defect severity.

JTAM, Sofia, vol. 50 Issue 1 pp. 020-035 (2020), [Full Article]




STRUCTURAL OPTIMIZATION OF LINEAR VIBRATION ISOLATION SYSTEMS

Zh. B. Bakirov, M. Zh. Bakirov, G. D. Tazhenova, Zh. S. Nuguzhinov
Karaganda State Technical University, Kazakhstan


This article addresses the problem of structural optimization of linear vibration isolation systems in various actions. A generalized criterion is formulated. The criterion reduces the problem of finding the conditional extremum of the functionality to the finding of the absolute extreme. Equations for the generalized criterion are obtained by the transfer function for deterministic, arbitrary kinematic and force actions. The optimal transfer function of the vibration isolation system is determined in the process of optimal synthesis. The solution to the problems of optimal synthesis for kinematic and random effects is given in the form of "white noise" and an exponentially correlated process, as well as by determined harmonic kinematic impact.

JTAM, Sofia, vol. 50 Issue 1 pp. 036-049 (2020), [Full Article]




THE RESEARCH OF MICRO-HARDNESS OF SIDE SURFACES OF TEETH CYLINDRICAL WHEELS PROCESSED BY "SHAVER-ROLLING DEVICE''

K. T. Sherov1, B. T. Mardonov2, T. M. Buzauova1, S. O. Tussupova1, N. S. Smakova1, A. S. Izotova1, R. Gabdyssalik3, T. B. Kurmangaliyev3, D. E. Elemes3
1Karaganda State Technical University, 100027, B. Mira str. 56, Karaganda, Kazakhstan
2Nawaii State Mining Institute, 210100, st. Galaba shokh 170, Navoi city, Uzbekistan
3D. Serikbaev East Kazakhstan State Technical University, 070004, St. Protozanova A.K., 69, Ust-Kamenogorsk, Kazakhstan


This article presents the results of the study of micro-hardness on the end surface along the involute tooth profile after processing with a rolling tool. The results of the study showed that the value of micro hardness obtained by processing with "shaver-rolling device" made of steel R6M5 is obtained within HB 263-271, and when processed with using "shaver-rolling device" made of ShH15 steel within HB 274-276. The results of experimental studies have shown that with an increase in cutting speed, the micro-hardness of the side and main working surfaces of the teeth wheel decreases. The most favorable results were obtained when processing tools is made of steel ShH15 at cutting conditions: n = 100–400 rpm; S = 0.2 mm/rotation.

JTAM, Sofia, vol. 50 Issue 1 pp. 050-056 (2020), [Full Article]




FINITE ELEMENT ANALYSIS OF ELASTOMERIC NETWORKS WITH FOCUS ON EFFECTS OF POROSITY

Mohammad Hossein Moshaei1, Payman Sharifi Abdar2, Mohammadreza Azmoodeh3
1Department of Mechanical Engineering, Ohio University, Athens, Ohio, US
2Department of Chemical and Biomolecular Engineering, Ohio University, Athens, Ohio, US
3Department of Mechanical Engineering, University of Tehran, Tehran, Iran


One of the common assumptions in analysis of polymer network on micromechanical level is the non-porosity of the polymeric media, but it is merely a simplifying assumption. This study dismissed this assumption and studies the polymeric networks with 10% and 20% porosity and compares them with a polymer media without porosity. To model the porosity in the polymer network, a random morphology is employed and using ABAQUS software, nonlinear finite element analysis is performed to study the structure of the porous polymer network. Comparing the networks with 10% and 20% porosity with the non-porous network shows the significant effect of porosity in mechanical behavior of the polymer network and how it can increase the maximum von-Mises stress remarkably.

JTAM, Sofia, vol. 50 Issue 1 pp. 057-069 (2020), [Full Article]




INFLUENCE OF MATERIAL NON-LINEARITY ON DELAMINATION IN MULTILAYERED THREE-POINT BENDING BEAMS

Victor Rizov1, Holm Altenbach2
1Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1 Chr. Smirnensky blvd., 1046 Sofia, Bulgaria
2Lehrstuhl für Technische Mechanik und Geschäftsführender Leiter Institut für Mechanik G10/58, Fakultät für Maschinenbau, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Deutschland


Delamination in multilayered three-point bending beam configurations is analyzed assuming non-linear behaviour of the material in each layer. For this purpose, an analytical approach is developed by using the Ramberg–Osgood equation. A solution for the strain energy release rate is derived by considering the energy balance. The strain energy release rate is obtained also by analyzing the complementary strain energy for verification. The solution derived is valid for a beam made of an arbitrary number of adhesively bonded horizontal layers of different thicknesses and material properties. Besides, the delamination can be located arbitrary between layers. The solution is applied for parametric investigations of delamination behaviour. The effects of delamination position along the beam height, material non-linearity and delamination length on delamination behaviour are evaluated. The results obtained in the present study are benefit to structural design of multilayered three-point bending beams exhibiting material non-linearity.

JTAM, Sofia, vol. 50 Issue 1 pp. 070-082 (2020), [Full Article]




SAINT-VENANT TORSION OF A FUNCTIONALLY GRADED CIRCULAR BAR WITH A RADIAL SLIT

A. Baksa
Institute of Applied Mechanics, University of Miskolc, Hungary


An analytical solution of Saint-Venant's torsion for circular bar with a slit extending in radial direction from the boundary to the axis of bar is presented. The material of the bar is non-homogeneous, isotropic linearly elastic. The shear modulus of the bar is a smooth function of the radial coordinate. This type of the material inhomogeneity is called functionally graded material. The shear modulus as a function of radial coordinate is assumed to be described by a power law function. For arbitrary value of power law index the solution in closed form is obtained for the Prandtl's stress function, shearing stresses, torsion function and torsional rigidity. Results of the presented analytical method are compared with FEM solution.

JTAM, Sofia, vol. 50 Issue 1 pp. 083-101 (2020), [Full Article]