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  1. Article: Investigation and Tailoring of Rotating Squares' and Rectangles' Auxetic Structure Behavior through Computational Simulations of 6082T6 Aluminum Alloy Structures.

    Elsamanty, Mahmoud / Elshokrofy, Hassan / Ibrahim, Abdelkader / Järvenpää, Antti / Khedr, Mahmoud

    Materials (Basel, Switzerland)

    2023  Volume 16, Issue 24

    Abstract: Auxetic structures, renowned for their unique lateral expansion under longitudinal strain, have attracted significant research interest due to their extraordinary mechanical characteristics, such as enhanced toughness and shear resistance. This study ... ...

    Abstract Auxetic structures, renowned for their unique lateral expansion under longitudinal strain, have attracted significant research interest due to their extraordinary mechanical characteristics, such as enhanced toughness and shear resistance. This study provides a systematic exploration of these structures, constructed from rigid rotating square or rectangular unit cells. Incremental alterations were applied to key geometrical parameters, including the angle (θ) between connected units, the side length (
    Language English
    Publishing date 2023-12-11
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma16247597
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: Friction Stir Welding of Dissimilar Al 6061-T6 to AISI 316 Stainless Steel: Microstructure and Mechanical Properties.

    Newishy, Mohamed / Jaskari, Matias / Järvenpää, Antti / Fujii, Hidetoshi / Abdel-Aleem, Hamed Ahmed

    Materials (Basel, Switzerland)

    2023  Volume 16, Issue 11

    Abstract: The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using ...

    Abstract The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead.
    Language English
    Publishing date 2023-05-30
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma16114085
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article: Tensile Properties and Deformation of AISI 316L Additively Manufactured with Various Energy Densities.

    Jaskari, Matias / Ghosh, Sumit / Miettunen, Ilkka / Karjalainen, Pentti / Järvenpää, Antti

    Materials (Basel, Switzerland)

    2021  Volume 14, Issue 19

    Abstract: Additive manufacturing (AM) is an emerging fabrication technology that offers unprecedented potential for manufacturing end-to-end complex shape customized products. However, building products with high performance by AM presents a technological ... ...

    Abstract Additive manufacturing (AM) is an emerging fabrication technology that offers unprecedented potential for manufacturing end-to-end complex shape customized products. However, building products with high performance by AM presents a technological challenge. Inadequate processing parameters, fabrication environment or changes in powder properties may lead to high defect density in the part and poor mechanical properties. Microstructure, defect structure, and mechanical properties of AISI 316L stainless steel pieces, additively manufactured by the laser powder bed fusion method using three different volume energy densities (VEDs), were investigated and compared with those of a commercial wrought AISI 316L sheet. Scanning and transmission electron microscopies were employed for characterization of grain and defect structures, and mechanical properties were determined by tensile testing. It was found that the number of defects such as pores and lack of fusion in AM specimens did not affect the strength, but they impaired the post-uniform elongation, more significantly when processed with the low VED. Twinning was found to be an active deformation mechanism in the medium and high VED specimens and in the commercially wrought material in the later stage of straining, but it was suppressed in the low VED specimens presumably because the presence of large voids limited the strain attained in the matrix.
    Language English
    Publishing date 2021-10-04
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma14195809
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article: Dissimilar Laser Welding of Austenitic Stainless Steel and Abrasion-Resistant Steel: Microstructural Evolution and Mechanical Properties Enhanced by Post-Weld Heat Treatment.

    Hietala, Mikko / Jaskari, Matias / Ali, Mohammed / Järvenpää, Antti / Hamada, Atef

    Materials (Basel, Switzerland)

    2021  Volume 14, Issue 19

    Abstract: In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical ... ...

    Abstract In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical properties, and effect of post-weld heat treatment (PWHT) at 250 °C of the dissimilar joints. The welding processes were conducted at different energy inputs (EIs; 50-320 J/mm). The microstructural evolution of the fusion zones (FZ) in the welded joints was examined using electron backscattering diffraction (EBSD) and laser scanning confocal microscopy. The hardness profiles across the weldments and tensile properties of the as-welded joints and the corresponding PWHT joints were measured using a microhardness tester and universal material testing equipment. The EBSD results showed that the microstructures of the welded joints were relatively similar since the microstructure of the FZ was composed of a lath martensite matrix with a small fraction of austenite. The welded structure exhibited significantly higher microhardness at the lower EIs of 50 and 100 J/mm (640 HV). However, tempered martensite was promoted at the high EI of 320 J/mm, significantly reducing the hardness of the FZ to 520 HV. The mechanical tensile properties were considerably affected by the EI of the as-welded joints. Moreover, the PWHT enhanced the tensile properties by increasing the deformation capacity due to promoting the tempered martensite in the FZ.
    Language English
    Publishing date 2021-09-26
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma14195580
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article: The Effect of Severe Shot Peening on Fatigue Life of Laser Powder Bed Fusion Manufactured 316L Stainless Steel.

    Rautio, Timo / Jaskari, Matias / Gundgire, Tejas / Iso-Junno, Terho / Vippola, Minnamari / Järvenpää, Antti

    Materials (Basel, Switzerland)

    2022  Volume 15, Issue 10

    Abstract: Severe shot peening (SSP) was used on additive manufactured 316L by laser powder bed fusion. The effect of the post processing on the surface features of the material was analyzed through residual stress measurements, tensile testing, hardness-depth ... ...

    Abstract Severe shot peening (SSP) was used on additive manufactured 316L by laser powder bed fusion. The effect of the post processing on the surface features of the material was analyzed through residual stress measurements, tensile testing, hardness-depth profiles, and fatigue testing by flexural bending. The results showed that SSP can be utilized to form residual stresses up to -400 MPa 200 μm below the surface. At the same time, a clear improvement on the surface hardness was achieved from 275 HV to near 650 HV. These together resulted in a clear improvement on material strength which was recorded at 10% improvement in ultimate tensile strength. Most significantly, the fatigue limit of the material was tripled from 200 MPa to over 600 MPa and the overall fatigue strength raised similarly from a low to high cycle regime.
    Language English
    Publishing date 2022-05-13
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma15103517
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article: Effects of Wall Thickness Variation on Hydrogen Embrittlement Susceptibility of Additively Manufactured 316L Stainless Steel with Lattice Auxetic Structures.

    Khedr, Mahmoud / Hamada, Atef / Abd-Elaziem, Walaa / Jaskari, Matias / Elsamanty, Mahmoud / Kömi, Jukka / Järvenpää, Antti

    Materials (Basel, Switzerland)

    2023  Volume 16, Issue 6

    Abstract: In the present study, the hydrogen embrittlement (HE) susceptibility of an additively manufactured (AM) 316L stainless steel (SS) was investigated. The materials were fabricated in the form of a lattice auxetic structure with three different strut ... ...

    Abstract In the present study, the hydrogen embrittlement (HE) susceptibility of an additively manufactured (AM) 316L stainless steel (SS) was investigated. The materials were fabricated in the form of a lattice auxetic structure with three different strut thicknesses, 0.6, 1, and 1.4 mm, by the laser powder bed fusion technique at a volumetric energy of 70 J·mm
    Language English
    Publishing date 2023-03-22
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma16062523
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article ; Online: Contactless online characterization of large-area conductive thin films by thermography and induction.

    Remes, Kari / Järvenpää, Antti / Fabritius, Tapio

    Optics letters

    2019  Volume 44, Issue 10, Page(s) 2574–2577

    Abstract: Testing and characterization techniques intended for traditional electronics production are rarely compatible with modern large-area, thin film electronics manufacturing processes such as roll-to-roll fabrication. Online quality monitoring of conductive ... ...

    Abstract Testing and characterization techniques intended for traditional electronics production are rarely compatible with modern large-area, thin film electronics manufacturing processes such as roll-to-roll fabrication. Online quality monitoring of conductive thin films is necessary for upscaling and maintaining high-yield production. Thermography has already shown its usefulness in these kinds of applications, but has suffered from the lack of proper non-contact electrical heating. Now a fully contactless quality inspection technique based on thermal imaging and induction heating is implemented and evaluated. This approach is capable of discovering defected areas and estimating conductivity degradation online with full coverage over conductive thin films.
    Language English
    Publishing date 2019-05-14
    Publishing country United States
    Document type Journal Article
    ISSN 1539-4794
    ISSN (online) 1539-4794
    DOI 10.1364/OL.44.002574
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  8. Article: Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg.

    Ahmadkhaniha, Donya / Huang, Yi / Jaskari, Matias / Järvenpää, Antti / Sohi, Mahmoud Heydarzadeh / Zanella, Caterina / Karjalainen, L Pentti / Langdon, Terence G

    Journal of materials science

    2018  Volume 53, Issue 24, Page(s) 16585–16597

    Abstract: High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were ... ...

    Abstract High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing.
    Language English
    Publishing date 2018-08-13
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2015305-3
    ISSN 1573-4803 ; 0022-2461
    ISSN (online) 1573-4803
    ISSN 0022-2461
    DOI 10.1007/s10853-018-2779-1
    Database MEDical Literature Analysis and Retrieval System OnLINE

    Full text online

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  9. Article: Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

    Ahmadkhaniha, Donya / Huang, Yi / Jaskari, Matias / Järvenpää, Antti / Sohi, Mahmoud Heydarzadeh / Zanella, Caterina / Karjalainen, L. Pentti / Langdon, Terence G

    Journal of materials science. 2018 Dec., v. 53, no. 24

    2018  

    Abstract: High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were ... ...

    Abstract High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing.
    Keywords X-ray diffraction ; corrosion ; deformation ; dielectric spectroscopy ; grains ; hardness ; magnesium ; microstructure ; sodium chloride ; tensile strength ; texture
    Language English
    Dates of publication 2018-12
    Size p. 16585-16597.
    Publishing place Springer US
    Document type Article
    ZDB-ID 2015305-3
    ISSN 1573-4803 ; 0022-2461
    ISSN (online) 1573-4803
    ISSN 0022-2461
    DOI 10.1007/s10853-018-2779-1
    Database NAL-Catalogue (AGRICOLA)

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