Volume 2, Issue 6 (June 2005)
A New Method for Opening Load Determination from Compliance Measurements
A brief review of the most popular compliance based methods for determination of the crack opening load is included in the introduction. This review reveals the demand for a noise resistant method that is especially needed in the near-threshold region where a partial crack closure prevails and the existing ASTM method does not calculate the correct opening load. With this in mind, a new technique was developed (‘Q’ method). It uses integration instead of differentiation of the compliance data. It also accounts for the partial crack closure situations. The derivation of the Q method is discussed together with its relation to the ASTM procedure, and both methods were used to analyze experimental data of 2324-T39 and 7475-T7351 Al alloys tested at 0.1 and 0.9 load ratios. On average the crack opening load values from the Q method are smaller by the factor of about 2/π in comparison to those obtained from the ASTM procedure.