Analysis of fatigue properties and failure mechanisms of Ti6Al4V in the very high cycle fatigue regime using ultrasonic technology and 3D laser scanning vibrometry

• Published in: Ultrasonics Vol. 53; no. 8; pp. 1433 - 1440
• Main Authors: Heinz, Stefan, Balle, Frank, Wagner, Guntram, Eifler, Dietmar
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2013
• Subjects: Amplitudes; Fatigue (materials); Fatigue failure; High cycle fatigue; Lasers; Stresses; Subsurface cracks; S–Nf curve; Three dimensional; Ti6Al4V; Titanium base alloys; Ultrasonic fatigue; VHCF; Subsurface cracks; VHCF; Ultrasonic fatigue; Ti6Al4V; S–Nf curve; S–N(f) curve
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2013.03.002

•Ultrasonic technology was used for accelerated fatigue experiments of Ti6Al4V.•Subsurface failures were observed in the Very High Cycle Fatigue regime.•Inhomogeneous phase distribution was found around the internal crack initiation site.•3D scanning vibrometry was used to describe the fatigue state of the specimen.•Non-contact strain measurements were realized at high frequently vibrating specimen. Accelerated fatigue tests with Ti6Al4V were carried out using a 20kHz ultrasonic testing facility to investigate the cyclic deformation behavior in the Very High Cycle Fatigue (VHCF) regime in detail. Beside parameters like the ultrasonic generator power and the displacement of the specimen, a 3D laser scanning vibrometer was used to characterize the oscillation and fatigue behavior of the Ti-alloy. The course of the S–Nf curve at the stress ratio R=−1 shows a significant decrease of the bearable stress amplitude and a change from surface to subsurface failures in the VHCF regime for more than 107 cycles. Microscopic investigations of the distribution of the α- and β-phase of Ti6Al4V indicate that inhomogeneities in the phase distribution are reasons for the internal crack initiation. High resolution vibrometry was used to visualize the eigenmode of the designed VHCF-specimen at 20kHz in the initial state and to indicate local changes in the eigenmodes as a result of progressing fatigue damage. Non-contact strain measurements were realized and used to determine the stress amplitude. The determined stress amplitudes were correlated with strain gauge measurements and finite element analysis.