An Evaluation of J-R Curve Testing Using Three Point Bend Specimens.
Research and Development rept.,
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER ANNAPOLIS MD SHIP MATERIALS ENGINEERING DEPT
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This investigation concerns the accuracy of load line deflection measurement techniques used in J integral-R curve testing of three point bend specimens bendbars. Four methods of load line deflection measurement were investigated. One method employed a calibrated transducer that gave a direct reading of load line deflection. The other three methods mathematically related load line deflection to some other displacement i.e. crack mouth opening displacement, cross head displacement measured during testing. Photographs taken at regular intervals during loading provided an absolute measure of load line deflection. In comparison to this reference, the other methods had equal accuracy with varying degrees of precision. In no case, however, did the measurements from the laboratory techniques deviate from the photographic reference by more than 0.052 mm 0.002 in. on average. The small differences between the load line deflections measured by the various laboratory techniques cause less scatter in the J-R curves and J sub IC values than attributable to material variability. Further, J-R curves over the first 1.75 mm of crack extension from both bendbars and compacts were shown to be coincident for the alloys tested. Author