Fabrication of artificial defects to study internal fatigue crack propagation in metals

Fatigue specimens designed with controlled internal defects were obtained by diffusion bonding of Ti-6Al-4V sheets containing femtosecond laser drilled notches. Crack initiation from the internal defect occurred systematically. The cracks were characterised by in situ synchrotron X-ray tomography. Propagation rates are lower than those of surface cracks of comparable sizes in the same material and fall between experimental data obtained for fatigue cracks propagating in air and in vacuum.