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A comparative study on the tensile properties of 3D printed ABS filament and resin: Effects of aging
No full textThis study investigates the effects of environmental aging on the tensile properties of 3D printed specimens using Fused Deposition Modelling (FDM), Stereolithography (SLA) and Digital Light Processing (DLP) technologies. Specimens are printed from Acrylonitrile Butadiene Styrene (ABS) filament and ABS-based resin. Tensile testing is conducted on samples directly after printing and then following aging periods of one month and two months in a controlled environment (23 °C, 55 % RH). Statistical analysis is performed using ANOVA to evaluate the influence of the printing method, material type, and aging time on tensile strength, Young’s modulus, and elongation at break. The tensile performance of FDM-printed specimens generally decreases over time, which is evident from the comparative analysis. Specimens aged for two months exhibit significantly reduced tensile strength compared to both unaged and one-month aged SLA specimens. Interestingly, one-month aged specimens show a slight improvement in tensile performance com-pared to unaged samples which is an unexpected outcome. On the other hand, DLP specimens display a clear sensitivity to the aging process, with a marked degradation in performance when subjected to tensile load over time. This highlights a lack of tolerance to aging in DLP 3D printed materials under mechanical stress.contract no. 451-03-136/2025-03/20010
STRUCTURAL MODIFICATION OF THE CARGO HOLD DOUBLE BOTTOM FOR A MULTI-PURPOSE VESSEL
No full textIncreasingly, modern maritime vessels must demonstrate sructural flexibility to accommodate the growing
need for transporting various cargo types in response to evolving industry demands. As a result, regulatory
bodies, and their respective rules, regulations and standards, require that novel structural solutions are to be
verified through advanced structural assessments, including finite element analysis (FEA). Therefore, this
study focuses on FEA-based structural assessment and optimization of the double bottom and underdeck
reinforcement structure in the two cargo holds of a multi-purpose vessel originally designed for bulk cargo.
However, the vessel now also needs to carry standard 20-foot high cube containers, imposing a significantly
different loading scenario. While bulk cargo results in nearly uniform load distribution, containerized cargo
introduces concentrated point loads. The analysis accounted for container weights, gravity, and accelerations
due to ship motion. Von Mises stress criteria were used to evaluate the structural response, according to the
rules and regulations of two major regulatory bodies: Lloyd’s Register and International Association of
Classification Societies. The results indicated that the original structure could not withstand the new loading
demands according to the regulatory standards. Consequently, structural modifications were proposed and
implemented. The study highlights that even multi-purpose vessels, which are assumed to be suitable for
various cargo types by design, require structural modifications to safely accommodate containerized cargo.
The presented solution demonstrates how targeted reinforcements can ensure compliance with modern
classification society rules while enabling operational flexibility.Project no. 451-03-137/2025-03/200105 from 4 February 202
PSO-BASED RESONANT CONTROLLER FOR TRAJECTORY TRACKING OF ROBOT MANIPULATOR
No full textThis paper addresses the problem of path following for robotic systems. Specifically, a robot manipulator with three degrees of freedom must consecutively track an elliptic curve in space while adhering to a prescribed velocity law. Given that robots are highly nonlinear mechanical systems, achieving this objective is a complex task. Therefore, the mathematical model of the robot manipulator is transformed into a more manageable linear form, based on the actuator dynamics. To achieve high-accuracy path following, a model-based resonant controller is proposed. While this type of controller is not novel within the control community, its application in robotics remains relatively unexplored. To minimize tracking error, a particle swarm optimization (PSO) algorithm is employed, with an appropriate objective function designed to achieve the desired goal. The primary contribution of this paper lies in the integration of this metaheuristic algorithm with the complex resonant controller. Extensive simulations are conducted for various velocities of the robot’s end-effector, and the results are consistent with the expected dynamic behavior.451-03- 137/2025-03/200105 from 04.02.2025
451-03-137/2025-03/20010
New Trends in Engineering Research 2024
No full textThis book is a collection of high-quality peer-reviewed research papers presented at the International Conference of Experimental and Numerical Investigations and New Technologies (CNNTech2024) held in Belgrade, Serbia, from 24 June to 27 June 2024. The book discusses various industrial, engineering and scientific applications of engineering techniques. Researchers from academia and industry present their original work and exchange ideas, experiences, information, techniques, applications and innovations in mechanical engineering, materials science, chemical and process engineering, experimental techniques, numerical methods and new technologies
Decision Support System for Ranking Risk Mitigation Measures at Mining Operator’s Workplace
No full textThe research work involved the development of a decision support system for
mitigating the risks of mining machinery operators. In this research, in contrast
to existing research, the prioritization of mitigation measures for risks in the
workplace was considered using the Risc Score analysis. Based on the ratio coefficient,
which is calculated as the quotient of the future value and the present
value of the risk, the effectiveness of the recommended mitigation measure. In
the paper, by applying the decision support system based on AHP structuring,
the prioritization of mitigation measures was carried out based on the ratio coefficient
as a weighting coefficient of the influential criterion of the effectiveness of
the proposed measure. Other influential factors in the AHP DSS model include
other criteria: the urgency of mitigation measures, pre-event/post-event, impact
on strategy, company policy, and others. The aim of the research is to emphasize
the importance of risk score analysis in the prioritization of mitigation measures
for mining mechanization operators, and it is transferable to other technical systems
as well
TRANSIENT MODELING OF IMPINGING HEAT TRANSFER FROM AN ACOUSTICALLY MODULATED TURBULENT AIR JET TO A NORMALLY POSITIONED FLAT SURFACE
No full textThe subject of this study is the numerical investigation of the impingement of an axisymmetric turbulent air jet on a flat surface, the influence of acoustic modulations on the coherent structures that form around the jet, and the effects on the heat transfer from the jet to the heated surface. The study showed how controlled acoustic perturbations influence the exit velocity profile from the nozzle and the formation of vortices in the boundary-layer of the jet. Since vortices are responsible for the redistribution of thermal energy transferred from the jet to the surface in impinging jet flow configurations, it is crucial to investigate whether their for-mation and evolution can be controlled. The results of the numerical simulations indicated very good agreement with experimentally measured velocity field. How-ever, a problem arises in the prediction of the heat transfer because the standard k-ε model overestimates the values of the heat transfer coefficient in the stagnation zone because they were theoretically developed to use shear stresses for the gen-eration of the turbulent kinetic energy, while in reality normal stresses are responsible for their generation in this flow situation. Due to the unstructured mesh used for the calculations, there are discrepancies in the results at larger edge distances. The complex flow at the impingement surface, the occurrence of secondary vortices and re-circulation zones and their direct effect on the heat transfer cannot be fully captured by the mathematical model, even if the numerical errors are acceptable compared to experiments
APPLICATION OF ULTRASOUND FOR DIFFERENT PURPOSES WITH EXAMPLES
No full textIn the last decade application of ultrasound has been increasing. The reason for this is that a wide range of frequencies can be utilized for various purposes. Different scientific fields describe ultrasound in their own way, and from an engineering point of view, the use of ultrasound is quite interesting. The purpose of this paper is to provide an overview of how ultrasound can be applied in diagnostics and welding, including practical examples. Also, during this research dependency between the measured echo of ultrasound wave and depth of founded irregularity is given
Аssessment of welded joints impact on structural integrity of a pressure vessel
No full textPrevious experience with integrity assessment of welded structures and elements had confirmed
the usefulness of numerical simulations, among other things in terms of how rigidity and geometry of such structures affect the stress distribution. This approach worked well for elastic calculations for welded structures, efficiently providing accurate results which were easy to compare with the yield stress levels of selected materials. In the case where stresses are above yield stress levels, the differences in mechanical properties of individual weld regions become a crucial factor in terms of influence on the integrity of the observed structure, unlike the elastic region, where this influence was negligible. In order to obtain proper input data (mechanical tensile properties of all welded joint
regions), previouslu developed methodology, that combines experimental and numerical method, is
used. Herein the experimental approach provided the strain fields (as obtained by digital image correlation) while specimen was subjected to tensile testing, which were used to improve numerical
computational models. In this way, it was possible to accurately determine the mechanical properties of all individual weld regions in an iterative manner. Using the previously described input data, two computational models of a pressure vessel were developed, with and without welded joints. During typical exploitation conditions under service operations, there was no difference between the two models, as the stresses were still in the elastic area. However, once the stresses reached plasticity, considerable differences between these models were observed in the welded joints area. Noticeable stress concentration was present in the zone of welded joints (in a computational model containing welded joints), increasing the stresses by around 50% (stress concentration factor of 1.5) in comparison to computational model without welded joints and without stress concentration. This had shown good agreement with previous research, which involved the application of this methodology to a pipeline, and these two cases were similar, since they involved welded structures made of shell elements loaded with internal pressure, causing membrane stresses.Project no. 451-03-137/2025-03/ 200105 from 04.02.202
NUMERICAL SOLUTIONS OF COMPRESSIBLE GAS FLOW IN MICROTUBE IN THE CONTINUUM REGIME
No full textUgovor br. 451-03-136/2025-03/ 200105 оd 04.02.2025. god
Analysis of rarefied gas flow in microchannels in slip and early transition regimes
No full textIn this paper, an analytical solution of two-dimensional, isothermal, compressible, subsonic and rarefied gas flow in a microchannel with slowly varying cross-section is considered. In order to increase the accuracy of the solution for the slip flow regime as well as to obtain solution for the initial part of the transition regime, the second order boundary condition is applied along with governing system of equations. The analytical solution of the differential equation was achieved by expressing the pressure in terms of the local values of the Knudsen number and the channel height, which enable the separation of variables. Thus, the distribution of pressure and velocity field is obtained indirectly based on the distribution of the local value of the Knudsen number. This approach highlights the significance of the Knudsen number as the main characteristic of the rarefied gas flow. The obtained analytical solution is significant because it allows for the accurate calculation of gas flow through microchannels of variable cross-section and can serve as a
benchmark for assessing the accuracy and reliability of numerical and experimental approaches to rarefied gas flow problems in microchannels.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The results presented here are the result of the research supported by the Ministry of Science, Technological Development, and Innovation, Republic of Serbia, Grant No. 451-03-65/202403/200105 (2024)