STP856

    Measurement of Stable Crack Growth Including Detection of Initiation of Growth Using the DC Potential Drop and the Partial Unloading Methods

    Published: Jan 1985


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    Abstract

    The ability of the DC potential drop method and the partial unloading technique to measure crack growth and to detect initiation of crack growth has been investigated using a number of steels and aluminum alloys. It was found that within the range of parameters investigated both of these methods can be recommended for the determination of the R curve; however, since at small amounts of crack growth, the DC potential drop method gave more consistent results, it is therefore considered to be superior. The initiation values Jo of the J integral determined by fractography were compared with JIc as obtained by current practice. It was found that ductile fracture toughness JIc is poorly related to initiation or to a specific amount of crack growth. A modification of the JIc procedure is proposed.

    Two contacting arrangements of the DC potential drop method were checked for initiation detection: one indicates initiation by a potential minimum (related to a J value Jmin), the other by the intersection of the R curve with the blunting line (related to a J value Jint).

    Keywords:

    fracture tests, cracks, crack propagation, DC potential drop method, partial unloading technique, initiation of crack growth, fracture toughness , J, Ic, multiple-specimen method


    Author Information:

    Schwalbe, K-H
    Head of department and research engineers, GKSS Research Center,

    Hellmann, D
    Head of department and research engineers, GKSS Research Center,

    Heerens, J
    Head of department and research engineers, GKSS Research Center,

    Knaack, J
    Head of department and research engineers, GKSS Research Center,

    Müller-Roos, J
    Head of department and research engineers, GKSS Research Center,


    Paper ID: STP34534S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP34534S


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