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    Crack Growth Resistance Measurement by Crack Opening Displacement Methods

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    In a previous investigation, tests had been conducted on compact specimens made of A508 Class 2A steel to study specimen geometry effects on JR-Curve behavior. No particular geometry effects were shown in specimens ranging in size from ½T to 10T when conditions for J-controlled growth were satisfied. These same specimens had been instrumented to develop crack opening displacement (COD) toughness values using a plastic hinge model. The COD-type R-Curve behavior was examined herein for specimen geometry effects and crack opening angle (COA) behavior.

    Plastic hinge (the position of a center of plastic rotation), COD, and COA were determined using a frame-type fixture that had been originally introduced by Andrew. The smallest specimen included herein was 1T and the largest was 10T. COD inferred from the plastic hinge model was determined at the original crack tip position (δ0) and at the advancing crack tip position (δt).

    Experimental COD and COA data and some theoretical evaluation schemes indicated that there is geometry-dependent δt versus Δap type R-Curve behavior. It was therefore concluded that JR and experimentally measured COD are incompatible with respect to geometry independence of R-Curve behavior. It was shown that the plastic hinge ratio is strongly influenced by ligament dimensions and that this hinge ratio ultimately controls the δt and δ0 values of COD once the plastic displacement becomes significant with respect to total displacement.


    cracks, crack opening displacement, crack opening angle, plastic hinge, JR, -Curve, compact specimens

    Author Information:

    McCabe, DE
    Westinghouse R&D Center, Pittsburgh, Pa.

    Ernst, HA
    Westinghouse R&D Center, Pittsburgh, Pa.

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP32578S