STP868: Fracture Toughness Testing of Ductile Cast Irons

    Salzbrenner, RJ
    Sandia National Laboratories, Albuquerque, NM

    Van Den Avyle, JA
    Sandia National Laboratories, Albuquerque, NM

    Lutz, TJ
    Sandia National Laboratories, Albuquerque, NM

    Bradley, WL
    Texas A&M University, College Station, TX

    Pages: 17    Published: Jan 1985


    Abstract

    The fracture toughness of ferritic, spheroidal graphite ductile cast iron has been measured by a single-specimen J-integral technique. The method used a servohydraulic test frame in the displacement control mode, with overall test control and data acquisition managed by a minicomputer. Digitized load and displacement values were combined to calculate incremental crack lengths based on measured crack length-compliance calibrations. Plots of J versus change in crack length were generated, and values of JIc (and equivalent KIc) were determined using ASTM Test for JIc, a Measure of Fracture Toughness (E 813). This technique thus provided a means of determining the plane-strain fracture toughness (KIc) using small samples (2.5 cm thick) at temperatures from −150 to +25°C. Previous attempts to measure KIc directly on similar materials had produced invalid results for all tests except those performed at very low temperatures (−60°C and below).

    Two ductile cast irons were investigated that had similar volume fractions of graphite, graphite nodule sizes, and ferrite grain sizes, but one contained approximately 15% pearlite, while the other had less than 1% pearlite. The alloy with greater pearlite content exhibited higher strength and higher ductile-to-brittle transition temperature. Although cast irons are generally perceived as being low in toughness, the toughness values measured on fully ferritic nodular iron were quite high (KIc = 80 to 106 MPa√m [73 to 96 ksi√in.] on the upper shelf).

    Keywords:

    fracture toughness, J, -integral, ductile cast iron, microstructure, nodular cast iron, load-controlled, displacement-controlled, fracture (materials), fracture mechanics, crack propagation


    Paper ID: STP34261S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP34261S


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