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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
Klasične analogije transporta količine toplote, supstancije i količine kretanja za slučaj strujanja fluida preko ravne ploče
No full textpo Ugovoru 451-03-136/2025-03/ 200105 оd 04.02.2025. god
The effect of natural aging on the tensile properties of PETG-CF filament
No full textParts manufactured using additive technology have been an excellent choice for prototyping for some time now. Certain materials, such as PETG, have shown a degree of similarity to metallic materials in terms of relationship between mechanical properties. These materials have demonstrated significant plasticity and toughness in the filaments, as well as the ability to form a "neck" during tensile testing.
Considering all of the above, the question arises as to whether PETG-CF can be used for manufacturing structural elements for smaller loads. In addition to standard tests, which have been performed many times, the question of aging has also emerged, i.e., the degradation of the mechanical properties of manufactured parts after a certain period.
This paper analyzes the change in strength between new samples and samples manufactured 10 months ago from the same PETG-CF filament
Advances in theapplication of Digital Image Correlations for evaluating bond strength between PMMA teeth and denture base
No full textFailure resistance represents a key mechanical property determining the durability of artificial teeth used in acrylic dentures. This study aimed to examine the biomechanical behavior at the interface between PMMA teeth and the denture base under different loading angles. Real-time measurements of force, strain, and displacement were conducted using the Digital Image Correlation (DIC) technique. Three groups of samples were tested: teeth with an unmodified basal surface, sandblasted surfaces, and bases with retention holes. Each group was subjected to loading at 45° and 90°, simulating clinically relevant angles that correspond to mandibular movements during mastication. To assess the effect of material ageing, half of the specimens underwent artificial thermal ageing prior to testing. The results demonstrated clear differences in force response, strain distribution, and displacement patterns among the groups, indicating distinct biomechanical behavior. Both loading angle and surface treatment significantly affected the bond strength between the PMMA teeth and the denture base. Deformation was mainly localized in the incisal region, while the highest strain values were observed in the lower parts of the specimens. Thermal ageing did not show a statistically significant effect on fracture resistance. Overall, PMMA teeth with mechanically prepared bonding surfaces exhibited higher fracture resistance compared to unmodified samples. The use of DIC provided detailed, spatially resolved insight into strain and displacement fields, offering a better understanding of interfacial mechanics between PMMA teeth and the denture base
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
ILC-MPC CONTROLLER FOR ROBOTIC MANIPULATORS BASED ON THE ULTRA-LOCAL MODEL
No full textThis research explores the possibility of simplifying model predictive control strategy for robotic manipulators and improving the control system’s performance with data-driven learning controllers. The main goal is to synthesize a controller that will be feasible for embedded hardware. Simplifying the robot dynamics is done using the ultra-local model method, and then new equations of motion are used to solve a nonlinear optimization problem in model predictive control. An iterative learning controller with a serial structure is added for increased performance when the given task is repetitive. Test simulation is carried out in Matlab to verify the feasibility of the proposed control system. Results of the simulation show that the proposed controller indeed manages to attenuate external disturbances and improve performance through the learning processNo. 451-03-137/2025-03/200105 from 04.02.2025;
No. 451-03-136/2025-03/20006
Primena i dimenzionisanje hidrociklona u papirnoj industriji
No full textKonstantni deo papir mašine je deo pripreme papirne mase između rezervoara u kome se skladišti razvlaknjena papirna masa i natočnog korita. Sastoji se od više tehnoloških celina koje obavljaju različite funkcije kao što su izdvajanje nečistoća, rafinacija, deaeracija (uklanjanje vazduha) i razvodnjavanje mase, tj. kontrola koncentracije čvrste materije, pre nego što papirna masa bude ravnomerno raspodeljena po širini papir mašine u natočnom koritu. Dobro projektovan sistem obezbeđuje kontinuirani protok suspenzije sa stalnom koncentracijom, kvalitetom i protokom, pri konstantnom pritisku, ka natočnom koritu. Poželjno je da varijacije protoka mase budu manje od 1% u odnosu na nominalnu vrednost. Hidrocikloni imaju ključnu ulogu u sistemu pripreme papirne mase jer poboljšavaju njenu čistoću pre nego što ona stigne do natočnog korita. Oni predstavljaju posebnu vrstu centrifugalnih prečistača koji uklanjaju neželjene čestice iz suspenzije, kao što su: pesak, druge čvrste čestice mineralnog porekla, metalne čestice, ostaci boje, plastika. Princip rada hidrociklona zasniva se na tangencijalnom ubrizgavanju papirne mase velikom brzinom, pri čemu se u uređaju stvara vrtložno kretanje. Zahvaljujući centrifugalnim silama, teže čestice (nečistoće) se potiskuju ka spoljnim zidovima i izlaze kroz otvor/priključak u donjem delu uređaja, dok tečna faza manje gustine, tj. prečišćena suspenzija izlazi kroz otvor/priključak u gornjem delu uređaja i nastavlja ka natočnom koritu. U ovom radu je analizirana primena hidrociklona u papirnoj industriji i prikazana je metodologija za dimenzionisanje i izbor ovih uređaja
OCCUPATIONAL HEALTH AND SAFETY RISK EVALUATION OF PM2.5 AIR POLLUTION DURING THE HEATING SEASON IN BELGRADE, SERBIA
No full textBelgrade has faced persistent air pollution for decades, with particulate matter concentrations frequently exceeding World Health Organization (WHO) limits during the heating season. Among major pollutants, fine particulate matter smaller than 2.5 μm (PM2.5) poses particular risks to health and has gained increasing attention in occupational safety and health research. This study examined the frequency of low-wind-speed days and the distribution of PM2.5 concentrations under such conditions to assess monthly risk levels during the heating season. Results show that October, December, and January are periods of elevated occupational health and safety risk. These findings highlight the need for preventive measures, such as shorter outdoor shifts, increased rest breaks, and task rotation, to reduce worker exposure to hazardous PM2.5 levels.under Contract No. 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
Evaluation of Firing Reliability and Penetration Depth of 3D Printed PLA Projectiles for 9x19 mm Ammunition
No full textRecent advances in 3D printing technologies and polymer materials have opened new possibilities in various engineering fields, including the defense industry. Among these developments, the concept of 3D printed ammunition has attracted growing attention due to its low cost, rapid prototyping potential, and material flexibility. However, this trend is also raising concerns regarding the reliability, safety, and possible misuse of such ammunition, especially given the limited
research available in this domain. In this study, several series of bullet projectiles were produced using an FDM 3D printer with PLA filament, designed according to NATO standards and integrated into live 9×19 mm ammunition. An experiment was conducted to evaluate firing reliability, weapon function, and target penetration behavior using a wooden board as a simplified terminal medium. All shots were successfully fired and analyzed in terms of operational consistency and penetration depth. Based on the experimental results, a preliminary analytical model was developed to support future research and enhance the predictive understanding of such projectiles. The results indicate promising potential for further development of 3D printed ammunition, with practical implications for both research and controlled applications