An Investigation into Impacting Techniques for Simulating Foreign Object Damage and Their Influence on the Fatigue Limit Strength of Ti-6Al-4V
Abstract
Foreign objects ingested into a gas turbine engine can cause a severe degradation of the fatigue properties of the impacted engine airfoils. Even small objects, such as sand, can cause damage that can reduce the fatigue capability of the material. Several factors have to be considered when evaluating the residual fatigue strength of an impacted material: a) the geometry of the impact damage such as the shape or stress concentration of a crater or dent, b) the role of residual stresses imparted to the material during the impact event, and c) the actual damage in terms of cracking or other microstructural damage. Ballistic impact was used as a baseline since it most closely represents an actual FOD event in an operating engine. To further understand the role of type of impact on the dynamic behavior of the material, other techniques were used to impart damage to the material. Specifically, quasi-static and low-speed pendulum impacts were used. Damage was imparted by these methods using the depth of the ballistic impacts as a reference. The baseline specimen used for this program was a diamond cross-section axial fatigue specimen with edges that were of similar geometry to the leading edge of a turbine engine airfoil. These leading edge specimens, machined from Ti-6Al-4V forged plate material in STOA condition, were fatigue tested in tension using a step loading technique. Half of the specimens were stress relief annealed prior to testing (post-impact) to eliminate residual stresses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2005
- Accession Number
- ADA469564
Entities
People
- Dennis J. Buchanan
- John J. Ruschau
- Steven R. Thompson
- Theodore Nicholas
- William J. Porter
Organizations
- Air Force Research Laboratory