Characteristics relevant to ductile failure of bimetallic welds and evaluation of transferability of fracture properties

Anssi Laukkanen (Corresponding Author), Pekka Nevasmaa, Ulla Ehrnstén, Rauno Rintamaa

    Research output: Contribution to journalArticleScientificpeer-review

    27 Citations (Scopus)

    Abstract

    Life management and structural integrity assessment of bimetallic welds in its state-of-the-art form relies on practical methods derived on the basis of years of experience in operation and simplistic strength of materials analyses. The complex conditions and properties of the weldment, as resulting from the elaborate interaction of different microstructures with gradients in material properties, have limited the ability of currently existing methods to construct the assessment on the basis of actual failure mechanisms of bimetallic welds. Current work addresses the assessment procedure by combining experimental and numerical fracture mechanics comprising a micro-mechanical evaluation of the relevant damage mechanisms. The studied dissimilar ferrite (SA508)-austenite (AISI 304) circumferencial weld is one with a Ni-enriched buttering layer. The experimental work comprises tensile and fracture mechanical characterization of the different microstructural zones of the bimetallic weld. Tensile properties are determined with microstructure specific flat bar specimens as well as round bar specimens enabling better inference of true stress-strain curves. Fracture resistance curves are established by applying small-specimen testing techniques. Different crack configurations are modeled by finite element analysis (FEA) to assess the relationships between fracture types, toughness and local near crack tip constraint parameters. Transferability and characterization question are considered by determining J-Q-trajectories and employing small-scale yielding corrections (SSYCs). On the basis of the experimental and numerical results and a fractographical investigation, the micromechanics of fracture are interpreted. Differences in strain hardening capacities of microstructural zones are found to most severely affect the toughness transitions of the weld and the associated failure modes. Two prime failure types are noted, one for cracks located at outer heat affected zone (HAZ) resulting in an unstable crack deflection towards the fusion line (FL) and another type associated with cracks positioned near the fusion line, wherein a low-toughness ductile fracture process results. Small fracture mechanics specimen is found applicable for fracture resistance determination of bimetallic weldments.
    Original languageEnglish
    Pages (from-to)1-15
    JournalNuclear Engineering and Design
    Volume237
    Issue number1
    DOIs
    Publication statusPublished - 2007
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    Welds
    toughness
    cracks
    crack
    fracture mechanics
    evaluation
    Toughness
    Cracks
    fracture strength
    Fracture mechanics
    fusion
    Fracture toughness
    Fusion reactions
    micromechanics
    microstructure
    heat affected zone
    strain hardening
    tensile properties
    failure modes
    crack tips

    Keywords

    • welding
    • welds
    • bimetallic welds
    • failure
    • failure analysis
    • failure mechanisms
    • ProperTune

    Cite this

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    title = "Characteristics relevant to ductile failure of bimetallic welds and evaluation of transferability of fracture properties",
    abstract = "Life management and structural integrity assessment of bimetallic welds in its state-of-the-art form relies on practical methods derived on the basis of years of experience in operation and simplistic strength of materials analyses. The complex conditions and properties of the weldment, as resulting from the elaborate interaction of different microstructures with gradients in material properties, have limited the ability of currently existing methods to construct the assessment on the basis of actual failure mechanisms of bimetallic welds. Current work addresses the assessment procedure by combining experimental and numerical fracture mechanics comprising a micro-mechanical evaluation of the relevant damage mechanisms. The studied dissimilar ferrite (SA508)-austenite (AISI 304) circumferencial weld is one with a Ni-enriched buttering layer. The experimental work comprises tensile and fracture mechanical characterization of the different microstructural zones of the bimetallic weld. Tensile properties are determined with microstructure specific flat bar specimens as well as round bar specimens enabling better inference of true stress-strain curves. Fracture resistance curves are established by applying small-specimen testing techniques. Different crack configurations are modeled by finite element analysis (FEA) to assess the relationships between fracture types, toughness and local near crack tip constraint parameters. Transferability and characterization question are considered by determining J-Q-trajectories and employing small-scale yielding corrections (SSYCs). On the basis of the experimental and numerical results and a fractographical investigation, the micromechanics of fracture are interpreted. Differences in strain hardening capacities of microstructural zones are found to most severely affect the toughness transitions of the weld and the associated failure modes. Two prime failure types are noted, one for cracks located at outer heat affected zone (HAZ) resulting in an unstable crack deflection towards the fusion line (FL) and another type associated with cracks positioned near the fusion line, wherein a low-toughness ductile fracture process results. Small fracture mechanics specimen is found applicable for fracture resistance determination of bimetallic weldments.",
    keywords = "welding, welds, bimetallic welds, failure, failure analysis, failure mechanisms, ProperTune",
    author = "Anssi Laukkanen and Pekka Nevasmaa and Ulla Ehrnst{\'e}n and Rauno Rintamaa",
    year = "2007",
    doi = "10.1016/j.nucengdes.2006.03.022",
    language = "English",
    volume = "237",
    pages = "1--15",
    journal = "Nuclear Engineering and Design",
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    TY - JOUR

    T1 - Characteristics relevant to ductile failure of bimetallic welds and evaluation of transferability of fracture properties

    AU - Laukkanen, Anssi

    AU - Nevasmaa, Pekka

    AU - Ehrnstén, Ulla

    AU - Rintamaa, Rauno

    PY - 2007

    Y1 - 2007

    N2 - Life management and structural integrity assessment of bimetallic welds in its state-of-the-art form relies on practical methods derived on the basis of years of experience in operation and simplistic strength of materials analyses. The complex conditions and properties of the weldment, as resulting from the elaborate interaction of different microstructures with gradients in material properties, have limited the ability of currently existing methods to construct the assessment on the basis of actual failure mechanisms of bimetallic welds. Current work addresses the assessment procedure by combining experimental and numerical fracture mechanics comprising a micro-mechanical evaluation of the relevant damage mechanisms. The studied dissimilar ferrite (SA508)-austenite (AISI 304) circumferencial weld is one with a Ni-enriched buttering layer. The experimental work comprises tensile and fracture mechanical characterization of the different microstructural zones of the bimetallic weld. Tensile properties are determined with microstructure specific flat bar specimens as well as round bar specimens enabling better inference of true stress-strain curves. Fracture resistance curves are established by applying small-specimen testing techniques. Different crack configurations are modeled by finite element analysis (FEA) to assess the relationships between fracture types, toughness and local near crack tip constraint parameters. Transferability and characterization question are considered by determining J-Q-trajectories and employing small-scale yielding corrections (SSYCs). On the basis of the experimental and numerical results and a fractographical investigation, the micromechanics of fracture are interpreted. Differences in strain hardening capacities of microstructural zones are found to most severely affect the toughness transitions of the weld and the associated failure modes. Two prime failure types are noted, one for cracks located at outer heat affected zone (HAZ) resulting in an unstable crack deflection towards the fusion line (FL) and another type associated with cracks positioned near the fusion line, wherein a low-toughness ductile fracture process results. Small fracture mechanics specimen is found applicable for fracture resistance determination of bimetallic weldments.

    AB - Life management and structural integrity assessment of bimetallic welds in its state-of-the-art form relies on practical methods derived on the basis of years of experience in operation and simplistic strength of materials analyses. The complex conditions and properties of the weldment, as resulting from the elaborate interaction of different microstructures with gradients in material properties, have limited the ability of currently existing methods to construct the assessment on the basis of actual failure mechanisms of bimetallic welds. Current work addresses the assessment procedure by combining experimental and numerical fracture mechanics comprising a micro-mechanical evaluation of the relevant damage mechanisms. The studied dissimilar ferrite (SA508)-austenite (AISI 304) circumferencial weld is one with a Ni-enriched buttering layer. The experimental work comprises tensile and fracture mechanical characterization of the different microstructural zones of the bimetallic weld. Tensile properties are determined with microstructure specific flat bar specimens as well as round bar specimens enabling better inference of true stress-strain curves. Fracture resistance curves are established by applying small-specimen testing techniques. Different crack configurations are modeled by finite element analysis (FEA) to assess the relationships between fracture types, toughness and local near crack tip constraint parameters. Transferability and characterization question are considered by determining J-Q-trajectories and employing small-scale yielding corrections (SSYCs). On the basis of the experimental and numerical results and a fractographical investigation, the micromechanics of fracture are interpreted. Differences in strain hardening capacities of microstructural zones are found to most severely affect the toughness transitions of the weld and the associated failure modes. Two prime failure types are noted, one for cracks located at outer heat affected zone (HAZ) resulting in an unstable crack deflection towards the fusion line (FL) and another type associated with cracks positioned near the fusion line, wherein a low-toughness ductile fracture process results. Small fracture mechanics specimen is found applicable for fracture resistance determination of bimetallic weldments.

    KW - welding

    KW - welds

    KW - bimetallic welds

    KW - failure

    KW - failure analysis

    KW - failure mechanisms

    KW - ProperTune

    U2 - 10.1016/j.nucengdes.2006.03.022

    DO - 10.1016/j.nucengdes.2006.03.022

    M3 - Article

    VL - 237

    SP - 1

    EP - 15

    JO - Nuclear Engineering and Design

    JF - Nuclear Engineering and Design

    SN - 0029-5493

    IS - 1

    ER -