Stress Ratio Effects on Small Fatigue Crack Growth in Ti-6Al-4V (Preprint)
Abstract
A systematic study of the effects of stress ratio on small fatigue crack growth in Ti-6Al-4V was conducted. Cylindrical fatigue specimens were tested axially at room temperature under a maximum stress of 690 MPa and with stress ratios (R) of 0.5, 0.1, and -1. Tests were periodically interrupted and a standard replication technique was used to monitor the growth of cracks artificially initiated from 30 to 40 micrometer micro-notches, which were milled into the specimen surface with a focused ion beam (FIB). Measurement of striation spacing from fracture surfaces was evaluated for determining small crack growth rates and showed good agreement with replication data, but is only possible for relatively high stress intensity factor ranges, delta-K, on the order of 10 MPa(square root m) or greater. A significant small crack effect is observed in this alloy, consistent with previous observations, where small cracks grew at stress intensity factor ranges below the long crack threshold and at higher rates than long cracks for equivalent delta-K levels.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2008
- Accession Number
- ADA502789
Entities
People
- M. E. Burba
- M. J. Caton
- R. John
- W. J. Porter
Organizations
- Air Force Research Laboratory