Development of a Procedure for the Calculation of J-R Curves From Pressed-Notch Drop Weight Tear Test Specimens

Abstract

Over the last few years, there have been ongoing efforts funded by TransCanada PipeLines Limited to develop a more fundamentally based procedure to extract a true measure of the dynamic steady-state fracture toughness of linepipe steels. As part of this effort, considerable research has focused on the drop-weight tear test (DWTT) specimen as the baseline specimen to be used in this development. Using instrumented DWTT test equipment, dynamic load-displacement histories were extracted from the experiments. In addition, a visual measure of the crack growth, and the crack-tip-opening angle (CTOA) were obtained from high-speed video equipment. A procedure has been developed using detailed three-dimensional finite element analyses that calculate the J-integral as a function of crack growth for these dynamic experiments. The results from these analyses have been verified using published procedures on similar scale specimens. This paper presents the development of a procedure for calculating the dynamic J-R curve from the load-displacement trace of a pressed-notch DWTT specimen. The slope of the JM-R curves generated provides technical insight into the range of steady-state propagation that occurs during these experiments. The slope of the JM-R curve (dJM/da) is compared to the visually measured CTOA values and conclusions about the relationship between these parameters and the steady-state propagation energy are made. These results are key in the development of a procedure to predict steady-state fracture propagation from laboratory specimen data.