Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Tensile properties of pure PLA polymer dedicated for additive manufacturing
No full textThis research aims to provide comprehensive data on PLA polymer tensile properties via conducted tensile tests on 100 % infill density specimens (for 0.3; 0.2; 0.1 mm layer height), and all possible lower infill results (i.e., from 90 to 10 %, with a 10 % increment) obtained by interpolation of previous research findings. Tensile tests are performed using dedicated ISO 527-2 standard. Next, the FEM analysis is performed for the 100 % case to verify the FEM model. Thus, the implemented constitutive models of this thermoplastic material and FEM simulations match the experimental data
Digitalization of Strategic Decision-Making in Manufacturing SMEs: A Quantitative SWOT-TOWS Analysis
No full textThe transition of contemporary manufacturing processes from digital to post-digital paradigms within the framework of Industry 5.0 necessitates the integration of both technological advancements and human-centered perspectives. This shift demands a high degree of customization and personalization in production processes, impacting both core and supporting operations. This study investigates the development of a software application designed to facilitate strategic goal-setting in manufacturing Small and Medium-sized Enterprises (SMEs) by leveraging a digitalized Strengths, Weaknesses, Opportunities, Threats (SWOT) analysis. The research focuses on the use of this tool to collect, compare, and rank SWOT factors provided by employees and managers, in order to support data-driven strategic decision-making. The initial phase of the study involved a sample of 520 entrepreneurs and business owners from Poland, Slovakia, the Czech Republic, Hungary, and Serbia, which led to the identification of an extensive list of 83 strengths, 92 weaknesses, 78 opportunities, and 86 threats. These factors were stored in a Google Cloud Database, enabling subsequent comparisons with new data. A further 63 senior decision-makers tested the application by entering their own SWOT factors, comparing them with existing ones in the database, and ranking their significance for strategic planning. The rankings were calculated automatically, with the top-ranked factors forming the basis for further analysis. In the final stage, these rankings were reviewed by five experts from the research consortium, who conducted pairwise comparisons and employed Analytic Hierarchy Process (AHP) analysis to develop a Threats, Opportunities, Weaknesses, and Strengths (TOWS) matrix. This matrix identified potential strategic actions to optimize operations within the investigated region. The findings demonstrate the potential of the software tool to enhance strategic decision-making and improve organizational performance in manufacturing SMEs. The results offer practical insights for decision-makers seeking optimal strategies for operational optimization in their organizations
New results on finite-time stability of nonlinear fractional-order multi-time delay systems: Delayed Gronwall inequality approach
No full textIn this paper, finite time stability (FTS) analysis of fractional-order nonlinear multi-time delay
systems is studied. By use of a fractional Gronwall inequality with time delay, new FTS criteria for proposed systems are established. Two numerical examples are given to illustrate the effectiveness of the obtained theoretical results
Green Ship Solutions for Sheltered Maritime Waters and Inland Waterways in the Western Balkans
No full textSince its introduction, the Green Deal and its incentives have encouraged a shift from road to waterborne transport to reduce greenhouse gas emissions and traffic congestion. In response, numerous initiatives have been undertaken to design ships and boats whilst incorporating green technologies. This study assesses existing and proposes new waterborne ship concepts that employ green and innovative technical solutions for the navigation in sheltered maritime waters and inland waterways of the Western Balkans. Despite their apparent differences, inland waterways, such as the Danube and Sava rivers in Serbia, and sheltered maritime waters and lakes, such as the Bay of Kotor and the Lake Skadar in Montenegro, share several characteristics: a limited range of navigation, reduced speeds to minimize ship-induced large disruptive waves, and the absence of significant weather-induced waves. These conditions make ideal testing ground for electric and hybrid vessel solutions. Despite challenges such as regulatory barriers, safety concerns, and the limitations of still-maturing technologies, this work demonstrates that some solutions are viable for such environments. Achieving this requires defining precise navigation conditions and ship requirements, while adhering to established principles of naval architecture
Impact properties of FDM-grade PLA material relative to infill density
No full textOne interesting feature of Additive Manufacturing (AM) is the ability to manipulate the internal structure of fabricated objects. In FDM (Fused Deposition Modeling) technology, the heated nozzle deposits the melted thermoplastic material onto a build platform. Namely, both the filling pattern and density can be controlled here. Depending on the slicer software, the filling pattern can be arranged in triangles, hexagons, cross lines, etc. The density can vary between 10-100%, with an increment of 10%. This research paper will focus on the influence of infill density on the impact properties of FDM-grade PLA material, i.e., how properties degrade with lower infill percentages. The full infill density spectrum (abovementioned) will be presented here. The authors’ previous research findings show the benefits of low layer thicknesses, in terms of result repeatability and impact strength values. Thus, the employed layer thickness here is 0.1 mm, the lowest resolution for most FDM machines. The impact tests are performed on an Instron CEAST 9050 instrumented Charpy test rig, mounted with a 5J hammer (see Fig. 1). The specimens are prepared according to the ISO 179-1:2010 standard, with seven specimens per condition
Nerazarajuća metoda određivanja sklonosti prema interkristalnoj koroziji nerđajućeg čelika X5CrNi18-10 (AISI 304) zasnovana na merenju električne provodljivosti
No full textU ovom tehničkom rešenju prikazano je ispitivanje stepena senzibilizacije na interkristalnu koroziju (IKK) i električne provodljivosti nerđajućeg čelika X5CrNi18-10 (AISI 304), da bi se dobila odgovarajuća korelacija. Stepen senzibilizacije određen je metodom elektrohemijske potenciokinetičke reaktivacije sa dvostrukom petljom (DL EPR), dok je električna provodljivost merena komercijalnim uređajem (nedestruktivna metoda). Nakon elektrohemijskog nagrizanja u oksalnoj kiselini, mikrostruktura površine uzoraka analizirana je skenirajućom elektronskom mikroskopijom (SEM). U slučaju kada je stepen senzibilizacije bio veći od ~ 0,5%, dobijena je jasna linearna zavisnost električne provodljivosti i stepena senzibilizacije, dok za niže stepene senzibilizacije postoji veće odstupanje od linearnosti. Pomenuta korelacija je razmatrana s gledišta kinetike taloženja Cr-karbida duž granica zrna i formiranja Cr-osiromašenih oblasti različitog stepena u blizini granica zrna. Cr-osiromašene zone tokom anodne polarizacije pokazuju manju otpornost prema obrazovanju pitova. Prisustvo Cr-osiromašenih zona u blizini granice zrna i smanjenje sadržaja ugljenika u austenitnoj kristanoj rešetki utiče na povećanje električne provodljivosti nerđajućeg čelika
Integracija aditivne tehnologije i mehaničke analize za epruvetu auksetičke strukture
No full textMaterijali sa negativnim Poasonovim koeficijentom su prepoznati kao auksetički materijali. Fleksibilna fotopolimerna smola je korišćena za uzorke, koji imaju auksetičku strukturu u vidu cilindrične školjke. Uzorci su štampani na LCD stampaču od fleksebilne smole koja strukturi daje elastična svojstva tokom testa sabijanja. Pomoću industrijske kamere dimenzionalne promene su zabeležene za dalja ispitivanja. Eksperimentalni rezultati metoda korelacije digitalne slike prikazuju različite scenarije za uzorke sa različitim dimenzijama strukture. Analizirani rezultati daju temelj za buduća istraživanja koja daju perspektivu potencijalnih aplikacija i proizvodnih varijacija auksetičkih struktura
Free Form Surface Machining – Comparation of Machining Strategies Using Commercial CAM Software
No full textFree-form surface machining is commonly performed using a ball end mill cutter on 3, 4, or 5-axis CNC machines. For this purpose, the use of commercial CAD/CAM software is indispensable, as it allows for the analytical description of the surface and the generation of NC code for machining. There are many commercial CAM software packages that facilitate tool path generation for free-form surface machining, enabling the use of various machining strategies according to the chosen CAM system.
This paper presents a comparison of machining strategies using Creo Parametric© software packages for free-form surface machining with a ball end mill cutter in 3-axis machining. For a generated CAD model of a free-form surface, a comparison of machining strategies was performed with special reference to machining time for different strategies, using the same input data to ensure consistent machining quality. High-speed milling (HSM) strategies were also included in the comparison.
In conclusion, it can be stated that the selected machining strategy has a significant impact, particularly on machining time, which in turn affects overall machining efficiency and cost
Tribological behaviour of hypereutectic Al-Si composites: A multi-response optimisation approach with ANN and Taguchi grey method
No full textAn optimisation model for small datasets was applied to thixocasted/compocasted composites and hybrid composites with hypereutectic Al-18Si base alloys. Composites were produced with the addition of Al2O3 (36 µm/25 nm) or SiC (40 µm) particles. Based on the design of experiment, tribological tests were performed on the tribometer with block-on-disc contact geometry for normal loads of 100 and 200 N, a sliding speed of 0.5 m/s, and a sliding distance of 1000 m. For the prediction of the tribological behaviour of composites, artificial neural networks (ANNs) were used. Three inputs were considered for ANN training: type of reinforcement (base alloy, Al2O3 and SiC), amount of Al2O3 nano-reinforcement (0 and 0.5 wt.%), and load (100 and 200 N). Various ANNs were applied, and the best ANN for wear rate (WR), with an overall regression coefficient of 0.99484, was a network with architecture 3-15-1 and a logsig (logarithmic sigmoid) transfer function. For coefficient of friction (CoF), the best ANN was the one with architecture 3-6-1 and a tansig (hyperbolic tangent sigmoid) transfer function and had an overall regression coefficient of 0.93096. To investigate the potential of ANN for the prediction of two outputs simultaneously, an ANN was trained, and the best results were from network 3-5-2 with a logsig transfer function and overall regression coefficient of 0.99776, but the predicted values for CoF in this case did not show good correlation with experimental results. After the selection of the best ANNs, the Taguchi grey multi-response optimisation of WR and CoF was performed for the same combination of factors as the ANNs. For optimal WR and CoF, the combination of factors was as follows: composite with 3 wt.% Al2O3 micro-reinforcement, 0.5 wt.% Al2O3 nano-reinforcement, and a load of 100 N. The results show that developed ANN, the Taguchi method, and the Taguchi grey method can, with high reliability, be used for the optimisation of wear rate and coefficient of friction of hypereutectic Al-Si composites. Microstructural investigations of worn surfaces were performed, and the wear mechanism for all tested materials was light abrasion and adhesion. The findings from this research can contribute to the future development of hypereutectic Al-Si composites
