Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Ballistic impact of fragment-simulating projectiles on steel targets: A multi-approach study
No full textPenetration mechanics, a subfield of terminal ballistics, examines the impact of projectiles (penetrators) on targets (obstacles) [1–3]. This study investigates the ballistic impact of fragment-simulating projectiles (FSPs) on homogeneous steel plates, a topic relevant to assessing the efficiency of fragmentation warheads and projectiles, as well as target vulnerability and protection. Three complementary approaches—experimental, analytical, and numerical—are employed to analyze the penetration process.
Extensive experimental research has been conducted [4, 5] and supplemented with new results. Two steel target plates, 1.25 mm and 2.20 mm thick, were perforated using blunt, deformable cylindrical projectiles with a diameter of 4.70 mm and two distinct masses—1.090 g and 1.912 g. Given the geometric characteristics and material properties of both the penetrator and the target, the dominant penetration mechanism was identified as plugging. Impact and residual velocities of the FSPs were measured, alongside the geometric properties of deformed penetrators and perforation holes in the target plates.
Various analytical models describing the plugging perforation process were examined. Additionally, a numerical model was developed in Abaqus using a Lagrangian framework with explicit time integration. The Johnson-Cook constitutive and failure models were employed to characterize dynamic stress and material failure. The analytical and numerical results were validated against experimental data, showing good agreement. This validation enables key conclusions regarding the influence of penetrator mass on residual velocity and provides an evaluation of the ballistic limit velocity.NITRA: 451-03-137/2025-03/200105 od 4.2.2025. god
THE ROLE AND SIGNIFICANCE OF PRIMARY WASTE SEPARATION IN SUSTAINABLEWASTE MANAGEMENT
No full textPrimary waste separation plays a crucial role in both environmental protection and public safety. In Serbia, over 90% of
waste ends up in landfills, with minimal recycling—opposite to EU standards. Such practices reduce landfill lifespan and waste
resource potential. Introducing source-level separation supports circular economy principles and aligns with the waste hierarchy,
where disposal is a last resort. Key steps include prevention, reuse, recycling, and energy recovery. Waste management begins at the
point of generation, making citizen education essential. This paper examines the importance of primary separation and the impact of
public awareness on municipal waste reduction
Drying Kinetics and Stability of Fatty Acids in Grape Pomace Seeds Under Mild Thermal Conditions
No full textGrape pomace, a significant by-product of the wine industry, is rich in
health-promoting compounds, including polyunsaturated fatty acids,
dietary fiber, and polyphenols, and holds strong potential for use in
functional foods and nutraceuticals. This study investigates the effects of
low-temperature convective drying at 40°C on the drying behavior and
fatty acid composition of grape seeds from ten Vitis vinifera L. cultivars.
To model the drying process, six thin-layer drying models were applied.
Among them, the Logarithmic model provided the best fit for most
cultivars, showing excellent agreement between predicted and
experimental drying curves. Effective moisture diffusivity values varied
considerably among cultivars, reflecting differences in pomace structure
and seed composition. Fatty acid analysis via gas chromatography
revealed that polyunsaturated fatty acids—particularly linoleic acid—were
the predominant lipid class in fresh grape seeds. After drying, a moderate
reduction in polyunsaturated fatty acids was observed, accompanied by a
corresponding increase in saturated fatty acids. Despite these changes,
certain cultivars, such as Prokupac and Merlot, retained favorable
nutritional profiles. The results support the application of mild drying
protocols to preserve the functional quality of grape seeds while improving
energy efficiency. This research contributes to the sustainable valorization
of grape pomace and highlights its potential applications, such as
functional oil ingredients, antioxidants in skincare, and encapsulated
nutraceutical formulations.Contract No. 451-03-137/2025- 03/200116 and Contract No. 451-03-137/2025-03/ 20010
A Note on the Fathers of Escalators: Ames, Souder, Reno, Wheeler, Seeberger
No full textEscalators (moving stairways) are machines which belong to the group of continuous conveying machines according to their principle of operation, but at the same time they are, together with elevators, classified as the machines for vertical transportation. In their historical evolution they have some points of contact, mostly because the manufactures of both equipment are the same; however, escalators differ substantially from elevators, which basic principles were formulated several centuries ago. The basic design employed has not varied from those patented more than a century ago. All relevant patents as a base for modern escalators have been developed in the second half of the 19th century. Individuals and engineers, who invented those first patents, are considered as fathers of escalators. In accordance with the sequence of inventions the key persons in the history of escalators are Nathan Ames, Leamon Souder, Jesse Reno, George Wheeler and Charles Seeberger. Brief notes from their life and work and their inventions are presented in chronological order.MSTDI of Serbia funded project “Integrated research in the fields of macro, micro and nano mechanical engineering”, contract number: 451-03-65/2024-03/200105, Faculty of Mechanical Engineering, University of Belgrade
VAT PHOTOPOLYMERIZATION RISK ASSESSMENT USING THE KINNEY METHOD
No full textAdditive manufacturing technologies are becoming increasingly prevalent across industries, educational institutions, and even households. Their primary application lies in the production of prototypes and components with intricate geometries. However, despite their widespread adoption, the potential risks these technologies pose to occupational safety and human health remain insufficiently explored. This paper presents a risk assessment of one of the most widely used additive manufacturing processes—Vat Photopolymerization. The evaluation was conducted using the Kinney risk assessment method to identify potential hazards associated with the technology. Based on the findings, appropriate safety measures were proposed to mitigate risks and enhance workplace safety
EVALUATION OF SPECIMEN GEOMETRY FOR RELIABLE MECHANICAL TESTING OF THERMOPLASTIC ALIGNER MATERIALS
No full textA thorough understanding of the variuos mechanical properties of thermoplastic materials is crucial for effective aligner treatment. The appropriate testing parameters and specimen shape for mechanical testing of aligners must be determined in order to obtain reliable results and accurate testing conditions. The aim of this study was to evaluate whether the rectangular shaped specimens, as proposed in previous studies, are suitable for Digital Image Correlation (DIC) testing. In this experimental study, a single type of material was used: Leone aligner PET-G sheet. Material was used in its original, uniformed, and flat form without thermoforming process prior to testing. Rectangular specimens of 1 mm thickness were laser cut to 20x5 mm. A total of five specimens were tested. Each specimen was spray painted with white and black acrylic paint to generate high contrast spots. All specimens were tested individually after fixing them manually in the universal testing machine. The tensile test was performed at speed of 1 mm/min. The specimens’ behaviour under load was evaluated using DIC method. The results showed that rectangular specimens did not consistently fracture in the central region where the stress was expected to be the highest. Instead, fractures occurred in the clamping areas, indicating that the stress concentrations were introduced by the fixation, rather than the material itself. Based on these results, rectangular specimens are not recommended for mechanical testing of aligner materials, as they showed inconsistent fracture locations and non-uniform strain distribution
Kinematic Modeling of the End-Effector of a Plum-Picking Robot Using the Rodrigues’ Rotation Formula
No full textThis paper presents the kinematic analysis of a designed end
effector for a plum-picking robot. The study includes solving both the
direct and inverse kinematics problems to determine the position and ori
entation of the gripper relative to the end-effector’s base. The kinematic
analysis is performed using Rodrigues’ transformation formula, ensuring
an accurate representation of rotational motion. All robot parameters
are derived from the designed model in SolidWorks, providing a realis
tic basis for the mathematical model. In addition, a workspace analysis
is performed to evaluate the reachability and efficiency of the robotic
system in the fruit picking process. The results obtained offer insight
into the capabilities of the system and contribute to the optimization of
robotic harvesting by ensuring precise motion control.451-03-137/2025 03/200105 from 04.02.202
Investigating the Ability of Turbulence Models to Predict Stall
No full textA detailed numerical study of the flows around the airfoil NACA 23012 near stall, at angles-of-attack ranging between 12.4° and 16.2°, Mach number M = 0.18 and Reynolds number Re = 1.8 million, was conducted by Reynolds-averaged Navier–Stokes (RANS) equations closed by the commonly employed Menter’s k–ω shear stress transport (SST) turbulence model in contrast to the wall-modelled large eddy simulation (WMLES). All these flow simulations were performed in ANSYS FLUENT on the same, sufficiently refined computational mesh with dimensionless wall distance y + ≈ 30. The comparison of the obtained numerical and available experimental results points to the inability of RANS modeling to adequately capture the flow in the post-stall region whereas it performs satisfactorily in the attached, pre-stall region. Although relative errors of lift and drag coefficients remain within an acceptable range, the numerical stall seems delayed or not predicted at all. On the other hand, WMLES manages to reproduce the expected trend of aerodynamic coefficients, while the actual numerical values appear underrated in comparison to the measured values. Both modeling approaches are critically evaluated with regard to the flow separation phenomenon appearing at airfoils at high angles-of-attack and some conclusions are provided
Impact properties of FDM-grade PLA polymer relative to infill density
No full textThis research paper focuses on the influence of infill density on the impact properties of FDM-grade PLA material, i.e., how impact properties degrade with lower infill percentages. Most FDM machines' infill density can vary between 10 % and 100 %. Here, we include the full infill density spectrum with an increment of 10 % (10 specimen groups). The authors’ previous research findings show the benefits of smaller layer heights regarding repeatability of results and impact strength values. Thus, the employed layer thickness here is 0.1 mm, the lowest resolution for most FDM machines. Tests were conducted at room temperature and a controlled humidity level of around 50 % on the Charpy instrumented pendulum.contract No.451-03-136/2025-03/200213 (from February 4, 2025)
Measuring the semantic priming effect across many languages
No full textSemantic priming has been studied for nearly 50 years across various experimental manipulations and theoretical frameworks. Although previous studies provide insight into the cognitive underpinnings of semantic representations, they have suffered from small sample sizes and a lack of linguistic and cultural diversity. In this Registered Report, we measured the size and the variability of the semantic priming effect across 19 languages (n = 25,163 participants analysed) by creating the largest available database of semantic priming values using an adaptive sampling procedure. We found evidence for semantic priming in terms of differences in response latencies between related word-pair conditions and unrelated word-pair conditions. Model comparisons showed that the inclusion of a random intercept for language improved model fit, providing support for variability in semantic priming across languages. This study highlights the robustness and variability of semantic priming across languages and provides a rich, linguistically diverse dataset for further analysis. The Stage 1 protocol for this Registered Report was accepted in principle on 15 July 2022. The protocol, as accepted by the journal, can be found at https://osf.io/u5bp6 (registration) or https://osf.io/q4fjy (preprint version 6, 31 May 2022).br. 451-03-65/2024-03/20010