Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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INFLUENCE OF LUBRICANT CONTAMINATION ON BALL BEARING RATING LIFE
No full textThis paper examines the service life of deep groove ball bearings, emphasizing a systems approach to service life calculation according to ISO 281. The contamination in the lubricant can accelerate wear and fatigue on the contact surfaces of bearings, leading to shortened service life. The paper investigates the influence of lubricant contamination on the service life of bearings using empirical data and established standard formulas. The resulting diagrams analytically show how service life varies depending on bearing size and operating conditions, such as lubricant viscosity, sealing efficiency, and load levels. The study's findings offer a more accurate understanding of ball bearing service life estimation under real operating conditions.Grant number: 451-03-137/2025-03/20010
CAVITATION RESISTANCE OF TALC-REINFORCED PYROPHYLLITE CERAMICS
No full textThe paper describes the effects of changing the properties of pyrophyllite ceramics reinforced with different
proportions of talc (%): 10; 20; 30. Pyrophyllite powders with a grain size of 20 μm and talc powders with
a grain size of 15 μm were homogenized, pressed and sintered at a temperature of 1200⁰C. The cavitation
resistance of the sintered samples was determined by the ultrasonic vibration method with a stationary
sample according to the ASTM G32 standard. The evolution of surface morphology and damage was
examined by scanning electron microscopy (SEM). The aim of the research was to obtain a compact
ceramic with improved properties of resistance to wear and cavitation. The quality of the sintered samples
was evaluated according to the values of cavitation rates and the analysis of the surface damage
THE CALIBRATION PROCESS OF THE “TRIMBLE - YIELD MONITORING” SYSTEM FOR THE PURPOSE OF YIELD MAPPING DURING THE TECHNOLOGICAL OPERATION OF BARLEY AND WHEAT HARVESTING
No full textThe application of modern technologies such as sensors and GPS as well
as the collection, analysis and management of production data have become standard in
precision agriculture. Yield, the main goal of production, is not only the post-harvest value,
but also provides important information when measured spatially and analysed accurately.
Yield mapping involves collecting data from multiple locations within a plot and creating
a spatial representation of yield variation. This approach provides information about
the heterogeneity of the field and enables informed decisions and planning of subsequent
management measures. The experiment was conducted during the wheat and barley harvest
in 2024 in the South Banat region. A New Holland CR 7.90 combine harvester was equipped
with a Trimble Yield Monitoring System, which includes an optical mass flow sensor and
an Ag Leader moisture sensor to record yield data. The recorded parameters of grain
moisture, harvested mass and hectolitre weight were then used to calibrate the system. The
calibration reduced measurement errors to around 2% for harvested mass and 0.2% for grain
moisture, ensuring high accuracy of yield data. This paper presents the entire process of
installing and calibrating the yield mapping system.contract registration number: 451-03-137/2025-03/20010
SMOOTHING OF DRAFT FORCE SIGNAL DURING PLOWING BY SAVITZKY - GOLAV FILTER
No full textThe measurement of draft force and soil resistance during plowing can be
performed using a strain transducer. They are placed on the lower tractor links, two sensors
on each side. After calibrating the sensors, acquiring and processing the data, the draft force
Fout and Fin are obtained, which correspond to the measurements on the two sensors on the
outside of the arms and the measurements on the sensors on the inside of the lower links.
Extreme values of the force signal as a function of time are extremely pronounced due to
changing conditions during the measurement. This paper investigates the influence of one
of the possible Savitzky-Golav smoothing signal filters. First, the appearance of the force
maps is shown in the experimental field of dimensions 120x60 on which the force effect is
most uniform. The corresponding diagram is also given with a display of the signal based on
the sensor measurements. Then, the data is filtered and the appearance of the new signal
diagram is given. Descriptive statistics finally provides a measure of the influence of the
applied filter. Statistical parameters have shown that the influence of the investigated filter
is minimal.contract registration number: 451-03-137/2025-03/20010
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
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
Feedrate profile generation with axis constraints using NURBS toolpaths for a Delta-KEOPS parallel kinematics machine
No full textIn numerical control feedrate profile defines the end effector or tool velocity tangent to the desired toolpath. By generat ing an appropriate feedrate profile smooth motion trajectories can be generated. Numerous papers propose a solution to this problem but most consider 3 and 5 axis cartesian machines. In this paper a computationally efficient feedrate profile generation algorithm is proposed for a Delta-KEOPS parallel kinematics machine with linear motor axes. The algorithm
generates a feedrate profile for complex shaped toolpaths defined by Non-Uniform Rational B-Splines (NURBS) while respecting the limitations of velocity, acceleration and jerk in the machines axes. This is a difficult task due to highly nonlinear kinematics of the Delta-KEOPS machine and complex shaped toolpaths. The algorithm was implemented in a PC-based real-time controller. Experimental results are presented which verify the capabilities and computational efficiency of the presented method on an actual machine
Risk assessment for hydrogen installations
No full textHydrogen is increasingly being adopted as a clean energy carrier across various industries, including transportation, power generation, and chemical processing. However, due to its unique physical and chemical properties—such as high flammability, low ignition energy, and wide flammability range—hydrogen poses specific safety challenges that must be carefully assessed and managed. This study presents a comprehensive risk assessment for hydrogen installations, focusing on identifying potential hazards, evaluating the likelihood and consequences of hazardous events, and assessing the effectiveness of existing safety barriers
APPLICATION OF LOGISTIC REGRESSION FOR IDENTIFICATION OF DROSS FORMATION CONDITIONS IN CO2 LASER CUTTING
No full textDross formation is an issue of multifold importance in laser cutting. In this study, based on data from two crossed experimental designs with 52 trials, a machine learning model, that is, multiple binary logistic regression, was developed to identify dross formation conditions in CO2 laser cutting. The model inputs were laser power, cutting speed, and oxygen pressure, and the corresponding dependent variable took the value of 1 (in the case of dross formation) or 0 (in the case of no dross formation). Statistical indicators showed a good predictive ability of the developed logistic regression model to discriminate between dross formation and no dross formation classes. It was revealed that the most decisive input regarding dross formation is the cutting speed. Upon the development of the logistic regression model, laser cutting process windows were created, and further analysis and interpretation of the experimental results were performed
The role of AI in architecture: fantasies and reality
No full textThe field of artificial intelligence (AI) has recently attracted the attention of many disciplines due to the exceptional accomplishments and rapidly emerging possibilities. Architecture, a discipline traditionally skeptical of new technologies, is intrigued by the results achieved with generative neural networks.
The emergence of new technologies in the field of generative artificial intelligence has led to numerous scenarios among architects about possible applications of these technologies in their practice. A large number of these scenarios are based on the functionality of commercially available Large Language Models and their application to text to image and image to image transformations. A smaller number of scenarios are based on specific applications of AI technologies through the development of real software solutions. The paper critically analyzes existing scenarios through a review of existing research and a description of software solutions. The focus is on the application of Generative Neural Networks and the paper provides an overview of the functioning of the basic classes of neural networks that make up this technology.
An analysis of how artificial neural networks work shows that they all depend on the data set used to train them. Today's neural networks use an enormous amount of data, but even that is limited to what is available in electronic format. The main source of general knowledge is online encyclopedias, while expert knowledge is provided by published articles that have a certain level of reliability. Architects who are mistrustful of this technology need to understand that better results can only be achieved through higher-quality training data sets and that their protectively guarded knowledge also comes from studying the work of other architects