Quantification of Drill Hole Damages in CFRP Laminates Using High-Resolution Ultrasonic Testing

This work investigates the detection and quantification of the damages incurred during the drilling process on a carbon fiber-reinforced polymer (CFRP) composite using nondestructive evaluation techniques of full waveform captured ultrasonic testing (UT) and comparing the damage quantification with X-ray micro-computed tomography ( $\mu $ CT) scan data. A methodology is presented to extract the 3-D damage surface from the captured UT data obtained from a 20-MHz spherically focused transducer, which can be later used for a structural simulation for the load reduction due to the presence of delaminations. Three samples are fabricated to demonstrate the methodology as well as the damage profile from different fabrication methods. Two samples are prepared using a precision drill press, while the third sample is drilled with a programmable drilling machine with a controlled feed rate. An immersion inspection system utilizing a spherically focused ultrasound transducer is used to capture the full waveform data from which the maximum effective radius of the drilled hole as well as the drilling-induced damage is extracted. The effective damage radius is measured through the thickness of the sample and compared to the $\mu $ CT data sets. A relation between the drilling practices as well as the sample quality to the average error between the analyzed UT and $\mu $ CT data sets is presented, with an absolute relative error between 1.2% and 6.0%.