EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In this work, we present a method to produce fatigue samples with controlled internal defects which are used to induce internal crack initiation. Diffusion bonding of metal sheets containing defects created by femto laser machining is used to produce sharp notches in the bulk of samples whose geometry and size enable to perform synchrotron tomography in situ fatigue tests (sample diameter section of the order of 1 mm). Ti-6Al-4V ELI alloy is chosen for its ability to initiate internal cracks (in the very high cycle fatigue regime), and also because this material can be joined by diffusion bonding . In situ experiments show that internal cracking systematically occurs at the notch. The propagation of those internal cracks is characterized in 3D. After approximately 50% of the fatigue life (for the stress level investigated) the cracks acquire a very regular quasi circular shape (Fig. 1), which is typically observed for internal cracks. The da/dN curves obtained are discussed with respect to crack growth literature data of the same material for tests performed in various environments.