Location of initiation sites in fracture toughness testing specimens-the effect of size and side grooves

Kim Wallin, Masamato Yamamoto, Ulla Ehrnstén

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

    2 Citations (Scopus)

    Abstract

    Cleavage fracture initiates usually at single locations in front of the fatigue crack in some position along the crack front. If the crack driving force along the crack front is uniform, one should expect the initiation sites to be randomly located along the crack front. Finite element analyses have, however, shown that the crack driving force varies along the crack front. Thus, the location of the cleavage initiation sites should reflect this variation in crack driving force. Fracture toughness specimens differ both in geometry and size. Also, the specimens may be side grooved or plane sided. All this can be expected to affect the local crack driving force along the crack front. The local crack driving force for cleavage fracture initiation can be divided into two components. The local KJ value describes the local effective stress intensity, whereas Q or Tstress describes the local constraint. To make things even more complicated, the local constraint is also affected by the local effective stress intensity. All of these are also affected by any ductile tearing occurring prior to cleavage initiation. The testing standards contain specific limitations on specimen sizes and their measuring capacity in order to ensure that the crack driving force in different specimens is sufficiently similar to make the results from different specimen types and sizes comparable. Classically, the fracture toughness test specimens have been comparatively large. Recently more and more work has been devoted to diminish the size of the specimens, to save material. One very promising specimen type is the miniature C(T) specimen with a 4 mm thickness and total height of 10 mm. Based on a recent international round-robin, the miniature C(T) specimen appears to provide compatible Master Curve T0 values as large specimens, but further validation regarding the similitude of the cleavage initiation is required, since the Master Curve is based on the assumption that specimen size does not affect this similitude. In this work, the location of cleavage initiation sites along the crack front are examined for different size and type of fracture toughness specimens, focusing on the miniature C(T) specimen. The location distributions are evaluated in terms of load level, specimen type, size and possible side grooving. It is shown that, as long as the standard requirements are fulfilled, the initiation location distributions for the miniature C(T) specimens are similar to larger conventional specimens. Side grooving is shown to have a minor effect on the initiator locations.
    Original languageEnglish
    Title of host publicationASME 2016 Pressure Vessels and Piping Conference
    Subtitle of host publicationCodes and Standards
    PublisherAmerican Society of Mechanical Engineers ASME
    Number of pages9
    Volume1B
    ISBN (Print)978-0-7918-5036-7
    DOIs
    Publication statusPublished - 2016
    MoE publication typeA4 Article in a conference publication
    EventASME 2016 Pressure Vessels and Piping Conference - Vancouver, Canada
    Duration: 17 Jul 201621 Jul 2016

    Conference

    ConferenceASME 2016 Pressure Vessels and Piping Conference
    CountryCanada
    CityVancouver
    Period17/07/1621/07/16

    Keywords

    • Testijng
    • Fracture toughness

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    Wallin, K., Yamamoto, M., & Ehrnstén, U. (2016). Location of initiation sites in fracture toughness testing specimens-the effect of size and side grooves. In ASME 2016 Pressure Vessels and Piping Conference: Codes and Standards (Vol. 1B). [PVP2016-63078] American Society of Mechanical Engineers ASME. https://doi.org/10.1115/PVP2016-63078