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    Use of the Direct-Current Electric Potential Method to Monitor Large Amounts of Crack Growth in Highly Ductile Metals

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    The direct-current electric potential method is receiving increasing attention for monitoring crack extension in J-resistance curve testing. Among its advantages over the unloading-compliance method are: (1) no time-consuming unloadings are required, (2) a continuous record of crack extension versus displacement can be obtained, and (3) the method can be used at higher strain rates where unloading compliance cannot be used.

    Despite the advantages of the direct-current electric potential method, questions persist regarding its ability to monitor large amounts of crack growth in highly ductile materials where large displacements and large amounts of plastic strain occur. This paper presents details of an experiment conducted on a 3T planform-size compact specimen of 25.4 mm thickness to assess the ability of the direct-current electric potential method to accurately measure crack extension in a highly ductile material. The material selected was Type 304 austenitic stainless steel. It was found that the Johnson expression, often used to calculate crack extension from direct-current electric potential data, significantly underestimated the actual amount of crack extension. However, a simple modification of the Johnson expression resulted in excellent agreement between calculated and measured crack extensions.


    electric potential, crack growth, austenitic stainless steel, Johnson equation

    Author Information:

    Marschall, CW
    Battelle, Columbus, OH

    Held, PR
    Battelle, Columbus, OH

    Landow, MP
    Battelle, Columbus, OH

    Mincer, PN
    Battelle, Columbus, OH

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP19015S