Volume 23, Issue 2 (March 1995)
A Full Field DC Potential Drop Calibration for an Asymmetrically Cracked M(T) Specimen
A direct current (DC) potential drop (PD) calibration tool, in the form of a computer program, is provided that can determine the PD response at any point in an M(T) specimen containing either a symmetric or asymmetric crack. Results from the program were verified using data in the literature and results from an analog simulation. If a standard PD calibration is applied to the PD response for an asymmetric crack, the total crack length will be underestimated which leads to significant stress intensity factor errors for even small amounts of asymmetry. Using the PD response of an asymmetric crack from an analog simulation, three methods to predict individual crack lengths are evaluated. The methods use a two-dimensional (2-D) iterative procedure to solve for crack length given voltages from at least two sets of probes located at different positions on the specimen. Any of the different methods, which use different probe locations as the calibration inputs, yield good crack length predictions for crack length to specimen width ratios a/W greater than 0.25. However, the most numerically robust method resulting in the least error over a large crack length range uses the PD from a centerline probe and the PD difference from two offset probes to predict the crack length. These predictions result in a crack length error that does not exceed ±0.004 W and consequently result in insignificant stress intensity factor errors.