Correlation of residual fatigue life with quantified NDE measurements

Quantified metrics from nondestructive evaluation (NDE) data were used to predict residual fatigue life of corroded AA2024-T3 specimens. The specimens were corroded under a wide range of conditions to achieve a range of corrosion morphologies, including a mix of pitting, intergranular, and general corrosion. Ultrasonic testing (UT), white light interference microscopy (WLIM), and microradiography images were then analyzed to extract damage metrics. The corroded specimens were then fatigued to failure. The resulting data were used to obtain an excellent correlation between the NDE metrics and the residual fatigue life using multiple linear regression (MLR). While there are several important metrics that can be extracted from UT and WLIM, the correlation with microradiography metrics was weak in this damage range. Residual life models including WLIM surface roughness measurements performed better for lightly damaged specimens than those using only UT measurements. However, the addition of microradiography metrics resulted in no significant improvement to the correlation models.