STP711: Significance of Crack Arrest Toughness (KIa) Testing

    Crosley, PB
    Associate director of research and president, Materials Research Laboratory, Inc., Glenwood, Ill.

    Ripling, EJ
    Associate director of research and president, Materials Research Laboratory, Inc., Glenwood, Ill.

    Pages: 17    Published: Jan 1980


    Abstract

    The statically calculated value of crack arrest toughness, KIa, is shown to be specimen-insensitive. The values of KIa fall within the same scatterband when the quantity is measured with tapered double cantilever beam (T-DCB) specimens, single-edge notched specimens, or modified compact specimens.

    The large amount of data collected from the ASTM Cooperative Test Program made it possible to statistically describe the dependence of KIa on crack jump length and KQ In a collection of data in which both KQ and KIa scatter, KIa will decrease in systematic fashion with increased crack jump length, and decreasing KQ, because of an ordering of the scattered data. This trend was found in the cooperative program data.

    Probably the most unequivocal method to determine the invariance of KIa is to examine it as a function of KQ. Thirty-five data points obtained by 12 different laboratories on two different types of compact specimens were available at the time this report was written. The standard deviation in KIa was less than 10 percent even though KQ varied by a factor of almost 2.5 to 1.

    Measurements of crack velocity and strains on T-DCB specimens justified the use of a static analysis for calculating KIa. Most of the time required for a run-arrest segment of crack extension is used in slowly decelerating the crack toward zero velocity. The strain measurements during this decelerating period are close to statically calculated values.

    The Reference Stress Intensity Factor, KIR, is conservative relative to KIa for SA533B Grade 1 steel at temperatures near and below the reference nil-ductility temperature (RTNDT). At mildly elevated temperatures, the curve appears to be nonconservative.

    Keywords:

    crack arrest, stress-intensity factor, pressure vessel steel, compact (, K, Ia, ) specimen, wedge loading, brittle weld, crack jump, fracture toughness


    Paper ID: STP27455S

    Committee/Subcommittee: E08.93

    DOI: 10.1520/STP27455S


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