Normalization Method for Developing J-R Curves with the LMN Function

Abstract The normalization method has been used to develop J-R curves directly from load versus load-line displacement data without the need for on-line crack length measurement. This method, based on the original key curve-method, used the principal of load separation and an assumed functional form for the deformation function to determine a calibration equation for each specimen being evaluated. Originally the functional form was a power law with two unknown constants. A new functional form (the LMN function) containing three unknown constants is proposed for use in the method of normalization. This function requires three calibration points, one more than was needed by the power law function. The LMN function is described in this paper, and the method for determining the three needed calibration points is given in detail. The procedure for using this new normalization method is describedin a step-by-step manner. Some results are included which show that this approach to normalization gives a J-R curve which agrees well with those developed from the elastic compliance method used in the ASTM test standards.