CALIBRATION OF AN ACPD MONITORING-SYSTEM FOR SMALL CRACK-GROWTH IN CORNER CRACK SPECIMENS

The development of an ACPD technique was essential to support stress c orrosion and corrosion fatigue crack growth studies in an Al-Zn-Mg all oy. The present paper reports calibration of the system for small part -through cracks in a small section corner crack specimen geometry. The calibration was carried out by empirical and analytical methods. Resu lts show that the relationship between normalised PD and crack length is a power law. The calibration curves depend on the spacing of the PD probe wire with higher resolution achieved at a smaller span. However , induced PD causes shifts in the voltage which also have to be consid ered. Corrections can be made by relating optical measurements of init ial and final crack lengths to the respective PD values. Fatigue resul ts confirm the effectiveness of the ACPD technique and the calibration procedures for quantifying small part-through crack lengths.