Use of Femtosecond Laser Technique for Studying Physically Small Cracks

Since small crack propagation behavior is strongly affected by microstructure, very small artificial notches with a length in the submillimeter range are needed for a systematic study of microcrack behavior. Laser processing technique with ultrashort pulses is a micromachining tool which will not cause any serious mechanical damage in metallic materials. Small artificial starter notches were manufactured in medium carbon steels with this technique and some fatigue tests were carried out. Laser affected zones could be observed at the notch boundary but cracks were initiated from the notch tips and propagated steadily. The crack paths were very tortuous like natural small cracks. The experimental results showed that the femtosecond laser processing technique is useful to introduce a small notch and allows systematic investigation of microcrack behavior.