Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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EFFECT OF SINTERING TEMPERATURE ON THE COLOUR VARIATION OF ANDESITE BASALT CERAMICS
No full textThis study examines the effect of sintering temperature in the air on the colour variation of ceramics produced from andesite basalt aggregate. Research has shown that a slight variation in sintering temperature by 10 °C, within the range of 1040 to 1080 °C, while maintaining a constant sintering duration of 60 min, results in noticeable colour variations in the sintered ceramic samples. After sintering and prior to analysis, the sintered samples were prepared using a standard method that included wet grinding with silicon carbide sandpaper of grit sizes P240, P400, P800, and P1200, followed by polishing with 1 μm diamond paste on a laboratory grinding and polishing device (Beta Grinder/Polisher, Buehler). Besides visual assessment, colour variations can be measured using colour classification systems, such as the CIELAB colour space, which is standardised by the International Commission on Illumination (Commission Internationale de l'Éclairage - CIE). The CIELAB system defines colour based on three parameters: L * representing lightness, a * indicating red-green intensity and b * denoting yellow-blue intensity. The sintered samples were analysed using a spectrophotometer (Shimadzu UV-2600) to measure diffuse reflectance in the 380–720 nm range, with a step size of 1 nm. Due to its outstanding physical properties and distinctive reddish-brown colouration, the polished sintered ceramic, processed at 1060 °C for 60 min, is highly suitable for producing of floor and wall tiles in the construction industry
МИНИМИЗАЦИЯ ВРЕМЕНИ ПРИ ОДНОВРЕМЕННОМ ПРОДОЛЬНОМ И ВРАЩАТЕЛЬНОМ ДВИЖЕНИИ КОНЬКА ЧАПЛЫГИНА
No full textАнализируется задача минимизации времени движения конька Чаплыгина в горизонтальной плоскости. В качестве управлений рассматривается сила, направленная вдоль вектора линейной скорости,
и вращающий момент. Применение принципа максимума Понтрягина позволяет установить, что
возможны три типа управления: регулярное управление, принимающее граничные значения («бангбанг») для силы и момента, сингулярное (особое) управление первого порядка для силы и сингулярное управление второго порядка для момента. Если управление является особым для силы на
всем интервале, то решение оптимизационной задачи неедиинственно. Участок особого управления
второго порядка может быть сопряжен с неособым участком только с помощью «чэттеринг»-режима.
Предлагается более простое субоптимальное управление, содержащее конечное количество переключений. Рассмотрены примеры для заданных конечных состояний полностью и частично заданных
конечных состояний, проведен анализ возможных комбинаций особых и неособых дуг траектории.Engleska verzija rada:
DOI: 10.1134/S106423072570062
COMPUTATIONAL MODEL FOR THE FATIGUE LIFE ESTIMATION OF CYLINDRICAL ROLLER BEARINGS
No full textThis study aims to obtain a computational model for the fatigue life estimation of cylindrical roller
bearings. For this objective, the maximum contact pressure, equivalent static Von Mises stress, and equivalent dynamic Von Mises stress were calculated. The effect of design parameters such as geometrical parameters, material parameters and loading parameters on the fatigue failure of rolling bearings was simulated. Equivalent dynamic Von Mises stresses were determined by considering both the alternating stress and mean stress. The fatigue life of cylindrical roller bearings was estimated by using Basquin’s equation. The results indicate that increasing the roller element radius and length reduces contact pressure and Von Mises stress, leading to an extended fatigue life. Conversely, higher elastic modulus and applied load increase stress levels and shorten bearing life. The findings provide insights for optimizing bearing design, highlighting the importance of selecting appropriate dimensions and materials to enhance durability and reliability.Contract No. 51-03-137/2025-03/ 20010
DEVELOPMENT OF A 2-AXIS SCARA ROBOT MOTION CONTROLLER BASED ON MCU
No full textThe robot systems are designed and developed in such a way that they can successfully realize the specified task. Robot control systems must enable control of robot movement and all other activities necessary for completing the programmed tasks. One of the most important parts of any robot is its motion, and precise control in real-time. This paper proposes the development of a robot motion controller based on the MIKROE MINI-M4 development board with the STM32F415RG microcontroller. Research related to the field of motion controller development presented in this paper includes the realization of interpolation tasks in joint coordinates (PTP control) and interpolation of linear path segments in world coordinates (CP control). To perform these tasks, a mathematical model of interpolation in joint and world coordinates of a two-axis robot with non-trivial kinematics is introduced. The interpolator model is developed so that the joints' or the end-effector's velocities have a trapezoidal profile. To achieve the required trapezoidal velocity profile, synchronized control sequences are generated as a series of pulses with appropriate frequencies for each axis. As a verification, before implementing the mathematical model into the motion controller, simulations of the mathematical model itself and the robot's motion in the joint and world coordinates are performed in the MATLAB environment. The motion controller is implemented on the aforementioned development board with a microcontroller (MCU) using the MIKROC programming environment. The series of pulses with appropriate frequencies is tested on an oscilloscope as the first verification method of the realized motion controller. Reference points of movement defined in joint or world coordinates are obtained by interpreting the program in the MATLAB environment and transferred via serial communication to the MCU with integrated motion control using the MIKROE EasyPIC V7 development board. Experimental verification of the developed motion controller was performed by laser engraving the programmed trajectory of the robot end-effector according to the desired PTP or CP motion control
Procedure for Integration of an Articulated Robot Model in а Game Engine Environment
No full textThe versatility and power of modern game engine platforms provide the potential for their use in creating real-time simulation environments within the robotics domain, particularly suitable for immersive and interactive experiences. Equipped with the comprehensive toolsets, extensive toolkits, and built-in features, these integrated development environments support the creation of real-time robot simulation models. Recently, Extended-Reality technology has been used in the development of human-machine interfaces in industrial robotics, in applications such as robot programming, system engineering, and personnel training. In this paper, the procedure for the integration of a vertically articulated robot’s model in the Unity game engine is presented. The main goal of the procedure is to generate a 3D GameObject robot in Unity, starting from a 3D model of the robot obtained using 3D design software. Positioning of robot joints’ local frames in a CAD environment for integration of a robot with Unity is described. The Articulation Body class from Unity’s built-in physics engine, Nvidia PhysX, is used to integrate robot dynamics. Specific XML formats following open-source standards, equipped with elements and attributes specific to robot kinematic and dynamic structure and suitable add-ons, have been used. The procedure is verified using the 6DoF vertically articulated robots RL15 and AD100
DIGITAL TWINS IN FRACTURE ANALYSIS OF PIPELINE MATERIALS: A REVIEW OF CURRENT APPROACHES AND METHODOLOGIES
No full textThis paper presents a review of recent research focused on the application of digital twins for fracture propagation analysis in ring-shaped specimens that simulate the behavior of thin-walled pipeline materials under loading. The emphasis is placed on the integration of the finite element method with fracture mechanics principles to predict stress intensity factors, J-integral values, and crack growth under complex geometries and loading conditions. The reviewed studies utilize numerical tools such as Simulia Abaqus, Ansys, and other commercial and open-source software, along with experimental methodologies for validating digital models. Special attention is given to iterative model calibration, the influence of geometry, material properties, and loading scenarios on prediction accuracy, as well as challenges related to standardizing procedures for structural integrity assessment. The paper identifies key directions for future research, including the development of comprehensive datasets for training AI-based models, advancement of multiphysics simulations, and the broader implementation of digital twins in real-world pipeline systems across the energy, petrochemical, and fluid transport sectors. This review contributes to a deeper understanding of the current state and potential of digital twins in fracture analysis and risk management in engineering practice
APPLICATION OF RULE BASED PARAMETRIC COMPUTER PRODUCT DESIGN
No full textThe use of Computer-Aided Design (CAD) systems is now ubiquitous in modern industry. Virtually no manufacturing company develops new products without some level of computer assistance. However, conventional constraint-based CAD modelling can be time-consuming—particularly in the context of Industry 4.0, where speed and automation are increasingly critical. This challenge is especially evident in companies that produce families of similar parts, where designers must repeatedly generate models from scratch.
Parametric modelling offers a solution by enabling automation in the development of new products. It allows external data tables to drive CAD models, making them interactive and accessible through web-based applications (e.g., via the World Wide Web). Such systems empower users without CAD expertise to interact with product models, thanks to embedded design rules that enforce constraints and automate calculations. These rules ensure product parameters remain within predefined limits or are derived from existing values.
In this study, a parametric CAD model of a universal press was developed using the commercial software Autodesk Inventor. The model integrates custom design rules and maintains full associativity with data stored in an external table. Automated regeneration of the assembly model was tested by altering input parameters, and the system's rule-enforcement functionality was validated. If rule conditions were violated, the CAD system triggered a user-defined notification window designed by the product developer.
This approach demonstrates a practical method for automating product development workflows, which can be customized to meet specific client requirements
On two inequalities of G. V. Milovanović and I. Ž. Milovanović and their applications
No full textIn this paper will be presented certain infinite dimensional generalizations of
two inequalities introduced by G. V. Milovanović and I. Ž. Milovanović [A
generalization of a problem given by D. S. Mitrinović, Publ. Elektroteh. Fak.,
Univ. Beogr., Ser. Mat. Fiz. 602–633, 129–132.], and some its applications.451-03-137/2025-03/ 200105 - 4.2.2025
“I mean, what are you talking about? You have the morals of an alley cat” – the negative evaluations of the political opponent in the 2024 US presidential debates
No full textThe paper focuses on the rhetoric of the two US presidential debates held in 2024 between the Republican and Democrat presidential nominees, the first between Joseph Biden and Donald Trump, and the second one between Kamala Harris and Donald Trump. We investigate the strategies of discrediting the political opponent, such as insults, pronoun-based oppositions, repetitions and three-part lists, and metaphors. It is shown that both the Republican and Democrat nominees abundantly used these devices and relied on similar argumentative strategies in the debates, which may have had an evaluative and persuasive function and deepened the political polarization. This has contributed to the impression of the predominantly hostile and polarizing rhetoric employed in the 2024 debates.br. 451-03-137/2025-03/20010
A Novel Grain Configuration for Dual Thrust Solid Rocket Motor Using Two Propellants
No full textThis paper presents the design of a propellant grain for a dual-thrust solid rocket motor, combining slotted and end-burner grain geometries with two propellants of different burn rates. This novel approach achieves a high thrust ratio between the two-phases while ensuring nearly neutral burning throughout motor operation. Key performance parameters, such as chamber pressure and thrust, can be predicted analytically, with experimental tests demonstrating excellent agreement with theoretical models. The proposed design offers several advantages: neutral burning in both phases, a highly flexible and high thrust ratio, rapid pressure reduction during phase transition, minimal sliver formation, and quick motor extinction at the end of the second phase. Additionally, the use of thermoplastic propellant technology allows for the integration of multiple propellants within a single grain, providing versatility in using cylindrical-shaped grains for various applications