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Iskalni niz: "polno besedilo" AND "organizacija" (Inštitut za kovinske materiale in tehnologije) .

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1.
Ladle melt treatment of high sulfur stainless steels
Jaka Burja, 2024, objavljeni znanstveni prispevek na konferenci

Povzetek: The influence of sulfur on both slag and melt is very important in steelmaking. This is especially true for highsulfur machining steels. Machinability is achieved by alloying high sulfur contents, above 300 ppm. These are steels that form small chips and shavings during mechanical processing by cutting, which is more appropriate and favorable for both the workpiece and the processing tool and machine. However, the secondary steelmaking slag is typically designed for desulfurization. This means that the sulfur content rapidly falls after sulfur additions. This is especially true for high machinability stainless steel grades where S contents can exceed 1000 ppm. This causes the sulfur wire yield to vary greatly in each charge, making the process unreliable. Some aspects of understanding the interaction between the steel melt and slag and the effect on casting are presented in this work. Based on industrial charges, we analyzed the yield of sulfur additions and the influencing factors on the efficiency of the sulfur addition. The lower slag basicity was linked to lover sulfur distribution rations, and lover sulfur distribution rations were linked to higher sulfur yields. Melt and slag samples were analyzed. Slag entrapment during ingot casting was linked to the high sulfur contents.
Ključne besede: desulfurization, sulfur, stainless steel, steelmaking
Objavljeno v DiRROS: 28.02.2024; Ogledov: 77; Prenosov: 23
.pdf Celotno besedilo (526,82 KB)
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2.
High temperature oxidation of EN AW 7075 aluminium alloy
Nejc Velikajne, Tilen Balaško, Jaka Burja, Matjaž Godec, Irena Paulin, 2024, objavljeni znanstveni prispevek na konferenci

Povzetek: Aluminium alloys are highly valued for their exceptional strength-to-weight ratio, making them a preferred choice in structural applications. Among these alloys, EN AW 7075 stands out for its superior mechanical properties, finding widespread use in industries such as aerospace, mechanical engineering, and sports equipment. This study investigates the high-temperature oxidation behavior of EN AW 7075 alloy. The gathered results can provide valuable insights into the behavior of the mentioned alloy during the selective laser melting (SLM) process. These results can contribute to a better understanding of how the alloy responds to specific conditions and parameters. SLM is an additive manufacturing technique. The process involves the sequential steps of preheating, melting, and rapid cooling of metal powder. To minimize the influence of oxygen, the build chamber is filled with inert gas. A protective argon atmosphere is continuously maintained. However, despite these precautions, oxidation can still occur, leading to potential issues in the final product. Hence, we examined the oxidation kinetics of the EN AW 7075 alloy in an oxygen atmosphere in the temperature range of 300-500 °C. The findings of this investigation significantly contribute to an understanding of the behavior of the alloy during high-temperature oxidation, particularly for ongoing studies focused on processing Al-Zn-Mg-Cu alloys using the selective laser melting technique. Thermogravimetry was employed to analyze the oxidizing behavior, with three samples subjected to a 6-hour exposure in an oxidizing atmosphere at temperatures of 300, 400, and 500 °C. Surprisingly, no oxidation occurred, as indicated by the negligible and negative changes in mass observed across all samples.
Ključne besede: EN AW 7075, high-temperature oxidation, oxide film, selective laser melting
Objavljeno v DiRROS: 28.02.2024; Ogledov: 73; Prenosov: 25
.pdf Celotno besedilo (897,18 KB)
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3.
Enhancing ductility of hot-work tool steel through isothermal bainitic transformation
Anže Bajželj, Aleš Nagode, Tilen Balaško, Barbara Šetina, Jaka Burja, 2024, objavljeni znanstveni prispevek na konferenci

Povzetek: Hot-work tool steels are extensively used in industrial applications that require high resistance to mechanical and chemical degradation at elevated temperatures. To meet these requirements, hot-work tool steels must exhibit good mechanical properties, including high tensile strength, hardness, wear resistance, and tempering resistance, as well as high thermal conductivity and ductility. This study investigates the ductility of the hot-work tool steel HTCS-130, which suffers from low ductility due to the presence of stable molybdenum-tungsten carbides (M6C) on the prior austenite crystal grain boundaries. Increasing austenitisation temperatures or prolonging the dwelling time at temperature can promote intensive migration of grain boundaries, leading to negative effects on the mechanical properties of the steel. To address this issue, isothermal transformation in the bainitic area between 350 and 500 °C was performed. Isothermal transformation at around 350 °C leads to the formation of lower bainite, which has similar hardness to tempered martensite. As the temperature of isothermal transformation increases, the hardness of the material decreases, due to the formation of upper bainite. The hardness analysis was measured using the Vickers method, the impact toughness of the steel samples was measured using a Charpy test with V-notched samples. The microstructure characterization was performed using optical and scanning electron microscopy. The improvement of ductility can be achieved by controlling the isothermal transformation of bainite and adjusting the heat treatment conHot-work tool steels are extensively used in industrial applications that require high resistance to mechanical and chemical degradation at elevated temperatures. To meet these requirements, hot-work tool steels must exhibit good mechanical properties, including high tensile strength, hardness, wear resistance, and tempering resistance, as well as high thermal conductivity and ductility. This study investigates the ductility of the hot-work tool steel HTCS-130, which suffers from low ductility due to the presence of stable molybdenum-tungsten carbides (M6C) on the prior austenite crystal grain boundaries. Increasing austenitisation temperatures or prolonging the dwelling time at temperature can promote intensive migration of grain boundaries, leading to negative effects on the mechanical properties of the steel. To address this issue, isothermal transformation in the bainitic area between 350 and 500 °C was performed. Isothermal transformation at around 350 °C leads to the formation of lower bainite, which has similar hardness to tempered martensite. As the temperature of isothermal transformation increases, the hardness of the material decreases, due to the formation of upper bainite. The hardness analysis was measured using the Vickers method, the impact toughness of the steel samples was measured using a Charpy test with V-notched samples. The microstructure characterization was performed using optical and scanning electron microscopy. The improvement of ductility can be achieved by controlling the isothermal transformation of bainite and adjusting the heat treatment conditions. These findings provide useful insights into the design and optimization of heat treatment processes for hot-work tool steels.ditions. These findings provide useful insights into the design and optimization of heat treatment processes for hot-work tool steels.
Ključne besede: hot-work tool steel, austempering, bainitic transformation, ductility, dilatometry
Objavljeno v DiRROS: 28.02.2024; Ogledov: 69; Prenosov: 24
.pdf Celotno besedilo (1,02 MB)
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4.
Effect of heat treatment on thermal conductivity of additively manufactured AISI H13 tool steel
Samo Tome, Blaž Karpe, Irena Paulin, Matjaž Godec, 2024, objavljeni znanstveni prispevek na konferenci

Povzetek: AISI H13 is commonly used for tooling, where higher wear resistance, thermal fatigue resistance, or hot toughness is required. Such examples include forging dies, plastic molds, hot shear blades, high-pressure die casting, and extrusion dies. Thus, thermal conductivity is one of the most important factors for hot work tools. Typically, the work cycle of a hot work tool designed for forging consists of four main phases: the forging stroke, with which the die imparts its shape onto the part, a brief pause while the die is reset to its original position, a lubrication phase, and a post lubrication dwell phase. During the forging phase, a significant amount of heat is transferred to the die while it is in contact with the part. This heat must then be dispelled for the part to return to a working temperature. While somewhat different, other hot work processes mentioned above are similar in that the hot work tool gets heated to a high temperature due to the contact with the object of deformation. The process of additive manufacturing (AM) promises better, more efficient tool production with features like conforming cooling channels, which would reduce the thermal fatigue of tools, prolonging tool life. However, the powder bed fusion (PBF) method creates a columnar microstructure, which has a detrimental effect on the thermal conductivity of H13 tool steel. Our investigation focused on the beneficial effect of heat treatment, specifically annealing at different temperatures, on the thermal conductivity of AM-produced H13 parts.
Ključne besede: SLM, thermal conductivity, tool steel, heat treatment
Objavljeno v DiRROS: 28.02.2024; Ogledov: 65; Prenosov: 27
.pdf Celotno besedilo (655,96 KB)
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5.
Development of the recycling procedure for rapid antigen tests
Rebeka Rudolf, Darja Feizpour, Žiga Jelen, Peter Majerič, Tilen Švarc, Matej Zadravec, Timi Gomboc, Aleksandra Kocijan, 2024, izvirni znanstveni članek

Ključne besede: rapid antigen tests, recycling, characterization, nanogold, plastic
Objavljeno v DiRROS: 28.02.2024; Ogledov: 74; Prenosov: 32
.pdf Celotno besedilo (1,74 MB)
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6.
A numerical study of gas focused non-Newtonian micro-jets
Rizwan Zahoor, Saša Bajt, Božidar Šarler, 2024, izvirni znanstveni članek

Ključne besede: serial crystallography, micro jets, multiphase flow, fluid rheology, non-Newtonian fluid, flow focusing
Objavljeno v DiRROS: 28.02.2024; Ogledov: 63; Prenosov: 28
.pdf Celotno besedilo (11,78 MB)
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7.
A hybrid radial basis function-finite difference method for modelling two-dimensional thermo-elasto-plasticity : Application to cooling of hot-rolled steel bars on a cooling bed
Gašper Vuga, Boštjan Mavrič, Umut Hanoglu, Božidar Šarler, 2024, izvirni znanstveni članek

Povzetek: This paper represents Part 2 of the parallel paper Part 1, where the strong form hybrid RBF-FD method was developed for solving thermo-elasto-plastic problems. It addresses the industrial application of this novel meshless method to steel bars cooling on a cooling bed (CB) where the formation of residual stress is of primary interest. The study investigates the impact of the distance between the bars and the distance to the heat shield above the CB on radiative heat fluxes and, consequently, on thermo-mechanical response. The thermal model is solved on bars cross-section with a RBF-FD method where augmented polyharmonic splines are used for the local approximation. View factors, computed with a Monte-Carlo method, are included in radiative heat fluxes. The thermal solution is incrementally applied on a mechanical model that assumes a generalised plane strain state and captures bars bending. The study employs a hybrid RBF-FD method to resolve a nonlinear discontinuous mechanical problem successfully. The simulation of the process shows how different process parameters influence the thermo-mechanical response of the bars.
Ključne besede: steel bars, cooling bed, thermo-mechanical modelling, hybrid radial basis function, generated finite differences, residual stresses
Objavljeno v DiRROS: 28.02.2024; Ogledov: 52; Prenosov: 28
.pdf Celotno besedilo (8,55 MB)
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8.
A hybrid radial basis function-finite difference method for modelling two-dimensional thermo-elasto-plasticity, Part 1 : method formulation and testing
Gašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, izvirni znanstveni članek

Povzetek: A hybrid version of the strong form meshless Radial Basis Function-Finite Difference (RBF-FD) method is introduced for solving thermo-mechanics. The thermal model is spatially discretised with RBF-FD, where trial functions are polyharmonic splines augmented with polynomials. For time discretisation, the explicit Euler method is employed. An extension of RBF-FD, the hybrid RBF-FD, is introduced for solving mechanical problems. The model is one-way coupled, where temperature affects displacements. The thermo-elastoplastic material response is considered where the stress field is generally non-smooth. The hybrid RBF-FD, where the finite difference method is used to discretise the divergence operator from the balance equation, is shown to be successful when dealing with such problems. The mechanical model is introduced in a plane strain and in a generalised plane strain (GPS) assumption. For the first time, this work presents a strong form RBF-FD for GPS problems subjected to integral form constraints. The proposed method is assessed regarding h-convergence and accuracy on the benchmark with heating an elastoplastic square. It is proven to be successful at solving one-way coupled thermo-elastoplastic problems. The proposed novel meshless approach is efficient, accurate, and robust. Its use in an industrial situation is provided in Part 2 of this paper.
Ključne besede: thermo-mechanical modelling, von Mises small strain plasticity, hybrid radial basis function generated finite differences, polyharmonic splines
Objavljeno v DiRROS: 28.02.2024; Ogledov: 61; Prenosov: 23
.pdf Celotno besedilo (2,69 MB)
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9.
Formulation of the method of fundamental solutions for two-phase Stokes flow
Zlatko Rek, Božidar Šarler, 2024, izvirni znanstveni članek

Povzetek: The method of fundamental solutions with a subdomain technique is used for the solution of the free boundary problem associated with a two-phase Stokes flow in a 2D geometry. The solution procedure is based on the collocation of the boundary conditions with the Stokeslets. It is formulated for the flow of unmixing fluids in contact, where the velocity, pressure field, and position of the free boundary between the fluids must be determined. The standard formulation of the method of fundamental solutions is, for the first time, upgraded for the case with mixed velocity and pressure boundary conditions and verified on a T-splitter single-phase flow with unsymmetric pressure boundary conditions. The standard control volume method is used for the reference solution. The accurate evaluation of the velocity derivatives, which are required to calculate the balance of forces at the free boundary between the fluids, is achieved in a closed form in contrast to previous numerical attempts. An algorithm for iteratively calculating the position of the free boundary that involves displacement, smoothing and repositioning of the nodes is elaborated. The procedure is verified for a concurrent flow of two fluids in a channel. The velocity and velocity derivatives show fast convergence to the analytical solution. The developed boundary meshless method is easy to code, accurate and computationally efficient since only collocation at the fixed and free boundaries is needed.
Ključne besede: Stokes equations, two-phase flow, free boundary problems, method of fundamental solutions, subdomain technique
Objavljeno v DiRROS: 28.02.2024; Ogledov: 61; Prenosov: 32
.pdf Celotno besedilo (3,40 MB)
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10.
An improved local radial basis function method for solving small-strain elasto-plasticity
Gašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, izvirni znanstveni članek

Povzetek: Strong-form meshless methods received much attention in recent years and are being extensively researched and applied to a wide range of problems in science and engineering. However, the solution of elasto-plastic problems has proven to be elusive because of often non-smooth constitutive relations between stress and strain. The novelty in tackling them is the introduction of virtual finite difference stencils to formulate a hybrid radial basis function generated finite difference (RBF-FD) method, which is used to solve small-strain von Mises elasto-plasticity for the first time by this original approach. The paper further contrasts the new method to two alternative legacy RBF-FD approaches, which fail when applied to this class of problems. The three approaches differ in the discretization of the divergence operator found in the balance equation that acts on the non-smooth stress field. Additionally, an innovative stabilization technique is employed to stabilize boundary conditions and is shown to be essential for any of the approaches to converge successfully. Approaches are assessed on elastic and elasto-plastic benchmarks where admissible ranges of newly introduced free parameters are studied regarding stability, accuracy, and convergence rate.
Ključne besede: Von Mises elasto-plasticity, radial basis function, finite differences, polyharmonic splines, two dimensions, hybrid discretization
Objavljeno v DiRROS: 28.02.2024; Ogledov: 63; Prenosov: 32
.pdf Celotno besedilo (5,24 MB)
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