Nondestructive evaluation of micro-cracks in a ceramic ferrule by resonant ultrasound spectroscopy

We performed a nondestructive evaluation of micro-cracks in ceramic ferrules for optical fiber connectors by resonant ultrasound spectroscopy (RUS). The ferrules were cylinders 10 mm in length and 2.5 mm in diameter. The acceptable ferrules had no cracks or ones below 5 μm and the defective ferrules had cracks from 5 to 25 μm in length. The acceptable ferrules could be distinguished from the defective ones statistically, even those with cracks of 5 μm, by comparing the differences between the resonant frequencies for both specimens.