Study of the Influence of Metallurgical Factors on Fatigue and Fracture of Aerospace Structural Materials
Final rept. 1 Jan 1983-31 Dec 1985
SOUTHWEST RESEARCH INST SAN ANTONIO TX
Pagination or Media Count:
This report summarizes the results of a two-phase study involving 1 experimental characterization and analytical modeling of fatigue crack tip micromechanics in aerospace structural Al and Ti alloys, and 2 identification and modeling of key factors controlling subcritical crack growth and unstable fracture in single crystal nickel-base superalloys. Fatigue crack growth at near-threshold rates has been modeled using micro-structurally- controlled micromechanical crack tip parameters. The model is based on the concept of crack opening by means of local slip lines whose length and dislocation density are controlled by the alloy microstructure. Crack tip opening displacement, crack tip strain, and the increment of crack advance are micromechanical parameters which depend on the number, spacing, and orientation of the slip lines. Fatigue crack growth mechanisms in Ni-base superalloy single crystals were examined as a function of crystallographic orientation, stress state and slip character. Using compact-tension and tubular specimens, fatigue crack growth in Mar-M200 single crystals of various crystallographic orientations was determined in both unidirectional and multiaxial cyclic loads, at temperatures where the slip character was either localized 25 C or homogeneous 980 C.
- Fabrication Metallurgy