Volume 35, Issue 1 (January 2007)
Influence of the Calibration Points on the Spb Parameter Behavior
The present work studies the separability parameter Spb behavior to estimate crack lengths when two or three calibration points are used. A set of precracked and blunt notched specimens with three-point bend ASTM-SE(B) geometry were prepared from three materials: AA 6061-T6 aluminum alloy with different side groove ratio, high-strength low-alloy welded steel, and 2.25Cr-1Mo steel. For each precracked specimen, initial and final crack length were measured on the crack surface. Intermediate crack lengths were determined by two methodologies: the standard elastic unloading and the Spb parameter method using two and three calibration points. The Spb crack lengths were very close to those estimated using the standard methodology; differences between them were less than 15 % Δa, suggested as a difference limit value in ASTM E 1820-99 to alternative methods for measuring crack extension. The performance of Spb parameter was evaluated using two and three calibration points. J-R curves were constructed. The JIQ values obtained by the standard methodology and the Spb method were similar.