| 1. |
- Dimitrios, Nikas, et al.
(författare)
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Effect of annealing on microstructure in railway wheel steel
- 2022
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Ingår i: 42Nd Riso International Symposium On Materials Science. - : Institute of Physics Publishing (IOPP). ; 1249
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Konferensbidrag (refereegranskat)abstract
- Railway wheels are commonly made from medium carbon steels (similar to 0.55 wt.% C), heat treated to a near pearlitic microstructure with 5-10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 degrees C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.
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| 2. |
- Stekovic, Svjetlana, 1967-, et al.
(författare)
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Effect of Nitriding on Microstructure and Mechanical Properties on a Ti64Alloy for Aerospace Applications
- 2022
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Ingår i: ICAS PROCEEDINGS. - Bonn.
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Konferensbidrag (refereegranskat)abstract
- Titanium is 40% lighter than steel and is very strong in relation to its low weight, which makes it veryinteresting for lightweight applications. However, the use of titanium in certain aircraft components islimited because titanium is a relatively soft metal that quickly deteriorates when mechanically stressed.In this research, a nitriding heat treatment has been developed for Ti64 (Grade 5) alloy with the aimto improve wear properties without negative effect on fatigue and strength. The mechanical propertieswere studied through hardness and wear tests performed at room temperature in laboratory air onuntreated and treated Ti64. Different measurements techniques were used to evaluate hardness onsurface as well as polished cross-sections due to uncertainties in hardness measurements of thinfilms. The wear properties were investigated with pin-on-disc tests. The microstructures and nitridedsurfaces were also investigated by optical microscopy, scanning electron microscopy (SEM) andsurface profilometry. The analysis has shown that the nitriding process has led to the formation of anuneven compound layer and a diffusion zone beneath it. The energy dispersive X-ray spectroscopy(EDS) mapping showed a high concentration of nitrogen in the compound layer and aluminium in thediffusion zone. The microhardness measurements and nanoindentation have revealed the formationof an approximately 2.5 μm thick diffusion zone. The wear tests results showed a large difference infriction behaviour between the nitrided specimens, which has been associated with the failure of thenitrided layer and the wear rate.
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| 3. |
- Cabo Rios, Alberto, 1990, et al.
(författare)
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Sintering anisotropy of binder jetted 316L stainless steel: part I–sintering anisotropy
- 2022
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 65:4, s. 273-282
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Tidskriftsartikel (refereegranskat)abstract
- In Binder Jetting (BJ) Additive Manufacturing (AM), green components are usually subjected to sintering process to reach required properties. Owing to the inherent low green density, binder jetted (BJ) parts undergo shrinkages up to 20%. In addition, anisotropic dimensional evolution during sintering is characteristic for BJ, generally caused by the specifics of the arrangement of particles during the printing process. In this study, the multi-axial dimensional evolution of 316L stainless steel cubic samples (10 × 10 × 10 mm3), manufactured using BJ, was characterised by dilatometry experiments. Dilatometry tests were conducted up to sintering temperatures of 1300°C and 1370°C, with a heating rate of 10°C/min and 5°C/min, respectively. Dilatometry results and final dimension measurements showed anisotropic shrinkage behaviour during sintering with about 15% larger shrinkage along the building direction. Shrinkages along the other two orthogonal directions were relatively similar, but a slightly larger final shrinkage along the printhead movement direction was observed. Relative density of 85.0% and 96.4% was obtained after sintering tests at 1300°C and 1370°C, respectively.
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| 4. |
- Areitioaurtena, Maialen, et al.
(författare)
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Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel
- 2022
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 96
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Tidskriftsartikel (refereegranskat)abstract
- The usage of induction hardening in the industry has increased in the last years due to its efficiency and repeatability. Induction hardening produces a hard martensitic layer on the specimen surface, which is accompanied by the generation of compressive residual stresses in the hardened case and tensile stresses in the untreated core. Residual stresses generated by induction hardening greatly impact on fatigue performance, as they act as crack growth retardants. In this work, a multiphysical coupled finite element model is developed to simulate induction hardening and compute the final residual stress state of the specimens along the microstructural transformations and hardness evolution. The impact of the transformation induced plasticity strain in the stress-state of the specimen during the process is also studied. The experimental validation shows that considering the transformation induced plasticity in induction hardening simulations improves the residual stress predictions, concluding that this effect should be included to achieve good residual stress predictions, especially in the subsurface region.
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| 5. |
- Balafendiev, Rustam, et al.
(författare)
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Wire metamaterial filled metallic resonators
- 2022
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 106:7
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study electromagnetic properties of a resonator recently suggested for the search of axions-a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of a wire medium works for this resonator without mesoscopic corrections, and that the resonator quality factor Q at the frequency of our interest drops versus the growth of the resonator volume V until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands-an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve wire medium loaded resonators.
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| 6. |
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| 7. |
- Bengtsson, Felix, et al.
(författare)
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Dataset: Alkali Ion diffusion and structure of chemically strengthened TiO2 doped soda-lime silicate glass
- 2022
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Annan publikationabstract
- Diffusion kinetics and structural properties of chemically strengthened titania-doped soda-lime silicate glasses were studied by depth-resolved X-ray photoelectron spectroscopy, Raman spectroscopy and spectrophotometry.Chemical strengthening (CS) is frequently used to strengthen thin glasses. CS of glass is based on ion exchange of larger ions from a molten salt into glass. Both the ion and counter ion are conventionally monovalent alkali ions.Diffusion kinetics and structural properties of chemically strengthened titania-doped (TiO2) soda-lime silicate (SLS) glasses were studied by depth-resolved X-ray photoelectron spectroscopy, Raman spectroscopy and spectrophotometry. The glasses were ion exchanged, whereby Na+ in the glass was replaced by K+ in a molten salt bath, at four different treatment temperatures between 350 and 500 °C.The following samples were prepared and analyzed by X-ray Photoelectron Spectroscopy (XPS): (1) SLS, (2) 4.7% TiO2, and (3) 9.9% TiO2. The ion exchange procedure was performed for 5 h at four different temperatures below Tg (350, 400, 450 and 500 °C). Before XPS measurements, the samples were wet-etched using hydrofluoric (HF) acid to produce samples with six different etching depths.The Raman scattered light was detected in the backscattering configuration employing linear polarization and 2400 lines/mm grating, and a 100x objective lens. Depth profile spectra were collected at six different depths of 0, 10, 20, 30, 40, and 50 µm for each glass sample, employing 12 scans with a 10 s exposure time for each scan.Spectrophotometric measurements were conducted before and after K+/Na+ ion-exchange treatmeatment for 5 h at 500 °C, collected between 300 and 2500 nm.
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| 8. |
- Heiskari, Janne, et al.
(författare)
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On the thickness determination of rectangular glass panes in insulating glass units considering the load sharing and geometrically nonlinear bending
- 2022
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Ingår i: Thin-Walled Structures. - : Elsevier BV. - 0263-8231. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- The number and size of windows has increased in large cruise ships, especially on the top decks. They have therefore become a weight and stability-critical component of the structure. Their thickness is determined according to the classification rules which are generalized for all type of passenger ships. That is, the provided formulae are based on linear-elastic, small deformation, plate theory and therefore more suitable for smaller windows in non-weight critical applications. However, majority of the windows are large insulating glass units (IGUs) that exhibit two e ects that the rules do not currently consider: development of membrane stresses in the glass panes at large deflections due to the von Karman strains (geometric nonlinearity) and interaction of the glass panes due to the internal cavity pressure between them (load sharing). Both increase the load bearing capacity of the IGUs. Therefore, extension to the thickness determination is needed for achieving the lightweight design. This paper uses nonlinear Finite Element Method to study the IGUs static response under uniformly distributed load considering the e ects. The response consists of principal stress and deflection of the panes, and the cavity pressure. Validation is carried out by experimental results from scientific literature. Case study on typical panes from cruise ships indicate that considering the two beneficial effects, the thickness of the glass panes in the IGUs may potentially be reduced between 26-54 % with respect to the classification rule-based design. That is, by using the same allowable principal stress criterion between the linear and nonlinear predictions.
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| 9. |
- Karlsson, Stefan, 1984-, et al.
(författare)
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Non-destructive testing of the glass strength in flat glass with indentationinduced cracks by Nonlinear Acoustic Wave method
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Glass is a unique but unfortunately brittle material whose strength is primarily limited by the presenceof cracks on the surface [1]. The strength of glass is limited by the fact that very high stresses arise atthe crack tips when subjected to tensile load. In principle, without the presence of surface cracks, glasswould have a strength far exceeding many other structural materials, e.g., steel. The size and thedistribution of surface cracks vary greatly, which results in the strength of glass exhibit a great variationand thus requires that large safety margins must be applied for glass in practical applications, e.g., whenused as a load bearing building material.Today, there are no methods to determine the strength of flat glass non-destructively. Instead, thestrength is determined by different experimental methods requiring >10 samples for sufficient statistics.This procedure requires both lots of glassy materials and time. The future aim is to investigate if the useof nonlinear acoustic waves (NAW) could be an alternative for developing a standardized designstrength value. Developing a non-destructive inspection method for determining the glass strength is ascientific breakthrough that will have a great industrial impact for the sustainable development of glassmanufacturing.With the use of NAW it is possible to detect and quantify the defects in materials [2,3]. The nonlinearwaves are transmitted through the object and the nonlinear effects, caused by the defects in thematerial, corresponds to the level of damage in the material. This work present result from samplescontaining relatively precise defects. The defects were created using a microindenter with a sufficientload to cause indentation induced cracking in the glass. The indentations were created using a Vickersdiamond tip in the middle of commercial 4 mm float glass samples of the dimensions 10x10 cm2. Theapplied loads were 0.5N, 1N, 2N, 5N and 10N. The “damage value” of the sample series was thenquantified using the NAW technique. The fracture strength of the samples was correlated destructivelyusing a conventional ring-on-ring setup.The results show that there is a clear correlation between the indenter load, the damage value from theNAW inspection and the fracture strength. We noted that the standard deviation for the ring-on-ringtests for the 1N, 2N, 5N and 10N was low while the 0.5N and the reference samples presented a highstandard deviation. A possible explanation for this observation is that for 0.5N not all indents give radialcracks but in some cases the indentation produces only plastic deformation. The main conclusion fromthe research is that is possible to detect realistically large defects in glass using the non-destructive NAWmethod and these defects cannot be seen with the naked eye. Moreover, the results can be directlycorrelated with the strength of glass [4].References[1] Veer, F.A. and Y.M. Rodichev, The structural strength of glass: hidden damage. Strength of Materials, 2011.43(3): p. 302-315. DOI: 10.1007/s11223-011-9298-5.[2] Persson, K., K. Haller, S. Karlsson, and M. Kozłowski, Non-destructive testing of the strength of glass by a nonlinearultrasonic method. Challenging Glass Conference Proceedings, 2020. 7. DOI: 10.7480/cgc.7.4498.[3] Haller, K., Doctoral Thesis: Acoustical measurements of material nonlinearity and nonequilibrium recovery.2008: Department of Mechanical Engineering, Blekinge Institute of Technology.[4] Karlsson, S., L. Grund Bäck, S. Andersson, K. Haller, M. Kozłowski, and K. Persson, Strength classification of flatglass for better quality – validation of method by well-defined surface defects and strength testing, in ÅForskReport,19-479. 2021: http://dx.doi.org/10.13140/RG.2.2.32992.40962.
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| 10. |
- Talebi, Nasrin, 1992, et al.
(författare)
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CRACK INITIATION CRITERIA FOR DEFORMED ANISOTROPIC R260 RAIL STEEL
- 2022
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Ingår i: CM 2022 - 12th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Conference Proceedings. ; , s. 857-864
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Konferensbidrag (refereegranskat)abstract
- Rail material selection and maintenance planning require accurate material failure criteria. While many of these criteria consider low-cycle fatigue of virgin materials, rail failure is known to occur after severe plastic deformations. It is, therefore, relevant to consider the applicability of such criteria during large plastic deformations. In this study, we simulate previously performed high-shear tension-torsion experiments using finite strain theory to evaluate the local stresses and strains. Based on these results, failure criteria are calibrated and validated. The Jiang-Sehitoglu criterion accurately fits and predicts failure. However, the identified parameter values are different from literature values for similar materials.
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