Effects of Crack Depth and Mode of Loading on theJ-RCurve Behavior of a High-Strength Steel

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Abstract
This paper describes an experimental program which had the objective of developing a series of J-R curve data from laboratory specimens of varied constraint. Constraint was varied by testing specimens with different thicknesses, crack lengths, and mode of loading. All specimens were relatively small and were kept simple in geometry and loading to allow estimation of the applied J integral. Crack length-to-width ratios were varied dramatically from a/W = 0.10 to a/W = 0.65 and the mode of loading ranges from three-point bending of deeply cracked edge-notched bars to pure tensile loading of double edge-notched strips. All tests were conducted on a single material, a high-strength structural steel, at ambient temperature, which is well up on the ductile upper shelf for this alloy.Results of these tests have shown that different constraint conditions can dramatically affect the JIc and the J-R curve for the full range of crack lengths and loading modes studied here, and these effects can be studied on relatively inexpensive laboratory specimens. Observed trends correspond to generally expected ideas of “increased constraint” or “decreased constraint” conditions, but since no factor is available to satisfactorily quantify constraint, an ability to utilize a data set such as this to predict the behavior of a material for a particular structural application is still lacking.
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