Iskanje po katalogu digitalne knjižnice

Opis: Knowledge of defect formation mechanisms in the manufacturing process helps improve product quality. In this study, defect formation due to re-melting of each layer in selective laser melting of Ti-6Al-4V demonstrated the physical behavior in the manufacture of metallic parts. The re-melting strategy was based on scanning with low energy density (ED) and increased ED with various combinations of laser processing parameters. The increased EDs and their parameters, namely laser power, scanning speed, and hatch distance, were selected based on the previous research experience by the authors. The concept of selecting a low ED followed by a high ED was to reduce the spattering of the powder material during the process. The low ED caused partial sintering of the powder, while the high ED caused the melting of the material, resulting in different metallurgical properties of the manufactured parts. Densities, pore properties, porosity in the initial layers, surface morphologies, and microstructures in the defective areas of the samples were studied to determine the effects of re-melting. Advantages and disadvantages were found with respect to the range of applications of the products
Ključne besede: re-melting, pore properties, defect, surface morphology, Ti-6Al-4V, selective laser melting
Objavljeno v DKUM: 14.03.2025; Ogledov: 0; Prenosov: 1
Celotno besedilo (16,16 MB)

Opis: This study addresses the inherent shortcomings of poly (lactic acid) (PLA), a biodegradable polymer widely used in industries such as packaging and biomedical applications. The principal challenge of PLA resides in its low crystallinity, which detrimentally affects its mechanical properties and thermal stability. Additionally, PLA is prone to water and hydrolysis, which compromises its chemical resistance and can lead to degradation over time. To overcome surmount these limitations, the study focuses on the development of hybrid films through the blending of PLA with poly (l-lactide-co-ethylene adipate) (pLEA) block copolymers. The objective is to augment the crystallinity, mechanical performance, and chemical resistance of the resulting materials. The study employs a range of analytical techniques, including Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Polarised Light Microscopy (PLM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA), to thoroughly characterize the copolymers and blend films. By systematically selecting blending ratios and processing methodologies, the study demonstrates enhancements in the properties of the resultant hybrid films compared to neat PLA. Specifically, the structure of films significantly changed from amorphous to crystalline in a short duration - 5 min, of annealing., leading to better tensile strength, modulus and reduced wettability, which are crucial for applications requiring durability and resistance to environmental factors. Films made from 30 wt% of pLEA 97.5/2.5 with 70 % of PLA by fast cooling exhibited outstanding mechanical properties, with a tensile strength 20 MPa higher than that of neat PLA films. Additionally, the chemical resistance may be improved, as evidenced by a decrease in wettability by approximately 15° and a reduction in the polar component of the surface free energy by about 7 mN/m. Hydrophobic, water-repellent materials resist penetration by water and other polar solvents, reducing exposure to corrosive substances and enhancing chemical resistance through barrier protection. Overall, this research addresses the limitations of PLA through innovative copolymerization and blending strategies, offering valuable insights into optimizing the material's properties for various practical applications.
Ključne besede: Poly(lactic acid), Poly(l-lactide-co-ethylene adipate), copolymer, blend, crystallinity
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 2
Celotno besedilo (10,53 MB)
Gradivo ima več datotek! Več...

Opis: This study investigates the predictive modelling of weld bead geometry in wire arc additive manufacturing (WAAM) through advanced machine learning methods. While WAAM is valued for its ability to produce large, complex metal parts with high deposition rates, precise control of the weld bead remains a critical challenge due to its influence on mechanical properties and dimensional accuracy. To address this problem, this study utilized machine learning approaches—Ridge regression, Lasso regression and Bayesian ridge regression, Random Forest and XGBoost—to predict the key weld bead characteristics, namely height, width and cross-sectional area. A Design of experiments (DOE) was used to systematically vary the welding current and travelling speed, with 3D weld bead geometries captured by laser scanning. Robust data pre-processing, including outlier detection and feature engineering, improved modelling accuracy. Among the models tested, XGBoost provided the highest prediction accuracy, emphasizing its potential for real-time control of WAAM processes. Overall, this study presents a comprehensive framework for predictive modelling and provides valuable insights for process optimization and the further development of intelligent manufacturing systems.
Ključne besede: wire arc additive manufacturing, WA AM, predictive modelling, machine learning, weld bead geometry, XGBoost
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 0
Celotno besedilo (3,54 MB)

Opis: Poly(ethylene 2,5-furan dicarboxylate) (PEF) based nanocomposites containing different nanoparticles like Ag, TiO2, ZnO, ZrO2 Ce-Bioglass, have been synthesized via in-situ polymerization techniques targeting food pack aging applications. Zeta potential measurements showed an increase in the negative zeta potential value due to an increase in the surface charge density of the nanocomposites. Thermogravimetric analysis results proved that, except PEF-ZnO nanocomposite, all the other nanocomposites exhibited good resistance to thermal degradation without serious mass loss until 330 ◦C. Thermal decomposition kinetic analysis and the dependence of activation energy on the degree of conversion (α), indicated that the presence of ZnO nanoparticles influences, the degradation mechanism of PEF. In contrast, the presence of Ce-Bioglass nanoparticles leads to a slower degra dation process, contributing to the enhanced resistance to thermal degradation of the PEF-Bioglass nano composite. The thermal degradation mechanism of PEF nanocomposites analyzed by pyrolysis‒gas chromatography/mass spectrometry (Py-GC/MS) indicated that the primary thermal degradation mechanism for the studied nanocomposites was β-hydrogen bond scission, while to a lesser extent, α-hydrogen bond scission products were noted in PEF-TiO2 and PEF-ZrO2 nanocomposites.
Ključne besede: bio based polymers, Poly(ethylene 2, 5-furan dicarboxylate), nanoparticles, thermal properties, nanocomposites, decomposition mechanism
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 3
Celotno besedilo (1,89 MB)
Gradivo ima več datotek! Več...

Opis: This paper explores a computational approach to model multiphase heat transfer and fuid fow in a natural circulation loop utilizing nanofuids. We propose and implement an Euler–Euler framework in a CFD environment, incorporating an innovative boundary condition to preserve mass conservation during thermophoretic particle fux. The model’s accuracy is verifed through a one-dimensional example, by comparing results against both an Euler–Lagrange model and an in-house fnite volume solution. Experimental validation is conducted with aluminum oxide nanofuids at varying nanoparticle concentrations. We prepared the nanofuids and measured their thermophysical properties up to 60◦C. We assess the thermal performance of the nanofuid in natural circulation loop at diferent heating powers via experiment and numerical simulations. The fndings reveal that the heat transfer enhancement ofered by the nanofuid is modest, with minimal diferences observed between the proposed Euler–Euler approach and a simpler single-phase model. The results underscore that while the Euler–Euler model ofers detailed particle–fuid interactions, its practical thermal advantage is limited in this context.
Ključne besede: CFD · Euler–Euler, multiphase fow, nanofluid, natural circulation loop, thermophoresis
Objavljeno v DKUM: 12.03.2025; Ogledov: 0; Prenosov: 3
Celotno besedilo (2,88 MB)