EFFECT OF CRACK CLOSURE ON ULTRASONIC DETECTION OFFATIGUE CRACKS AT FASTENER HOLES

摘要

The ultrasonic response from closed fatigue cracks grown in aluminium alloy specimensusing a representative aircraft spectrum loading has been characterised as a function of tensile appliedload using pulse-echo 45° shear-wave ultrasonic C-scans with focused immersion transducers.Observed trends with crack size and applied load are described and compared to results for artificialmachined defects. The results demonstrate that crack closure significantly reduces the ultrasonicresponse compared to open cracks or machined defects.