Structure-Property Relations in Aluminum-Lithium Alloys
Abstract
This work describes the effect of microstructure on the behaviour of small fatigue cracks in the two Aluminum-Lithium-Copper-Magnesium-Zirconium alloys 8090 and 8091. The slip distribution in these alloys was varied through thermo-mechanical processing. Although slip distribution affected tensile, cyclic and long fatigue crack behaviour, it did not affect small fatigue crack behaviour due to low levels of closure and reduced slip reversibility near to a free surface. Similarly, underageing and coverageing had no effect on small fatigue crack behaviour. Therefore, small fatigue crack growth is concluded to be insensitive to precipitate size and distribution. Due to differences in grain size, small fatigue cracks in 8091 were observed to propagate twice as slowly as in 8090. Small fatigue cracks grew more rapidly than long fatigue cracks under the same nominal Delta(k) and displayed no threshold behaviour. This was shown to be due to the combined effects of the low closure levels, high applied stresses and proximity to the surface. Low cycle fatigue behaviour was shown to be related to small fatigue crack behaviour and similar microstructural effects were observed. Total rather than plastic strain was identified as the critical parameter when comparing small fatigue crack and LCF behaviour. Theses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1989
- Accession Number
- ADA219183
Entities
People
- David J. Nicholls
Organizations
- Air Force Institute of Technology