The definition and measurement of crack closure

The theory supporting the conventional method of measurements of closure by using compliance measurements of Delta K(eff) and K(clo) is reviewed. It is shown that the conventional method of measurement of Delta K(eff) is equivalent to a calculation of Delta K via the change in compliance or energy release rate of the specimen. However, the use of Delta K(eff) involves certain simplifying assumptions which become unnecessary if Delta K is calculated from the energy change directly. This leads to the introduction of a new parameter, K(true), the use of which makes it possible to resolve some anomalies in the experimental data.