Mechanical Behavior of Advanced Aerospace Materials
Abstract
The effect of microstructure, environment, and coatings on mechanisms of fatigue and fatigue crack initiation and growth in TiAl intermetallic alloys has been investigated. For a gamma titanium aluminide alloy, the coarse and refined lamellar materials with colony sizes equal to 700 and 280 micrometers, respectively, have substantially greater crack growth resistance than does the fine duplex material with approximately 20 micrometers grain size. The influence of laboratory air on a wrought gamma TiAl alloy produces crack growth rates more than an order of magnitude higher than those observed in ultra high vacuum environment at temperatures ranging from ambient to 800 deg C. A twophase glass coating that exhibits a reduction in oxidation rate of an orthorhombic titanium aluminide, which was used as the matrix in a composite, fails to produce any enhancement in fatigue life. An extensive investigation involving fatigue, fatigue crack growth, mechanisms, modeling, and metallurgy of titanium matrix composites (TMC) is being conducted. Life models for isothermal and thermomechanical fatigue and crack propagation have been developed using concepts based on the maximum fiber stress, life fraction for time and cycle dependent response, matrix stress-life behavior, and fiber bridging. A model was developed for deformation, damage evolution, and failure of unidirectional TMC under sustained load. Effects of heat treatments on tensile and creep behavior of an orthorhombic neat matrix and on several continuous SiC fibers have been evaluated. Thermally induced stresses and damage progression in ceramic matrix composites due to fatigue and fracture are being studied. In monolithic materials, effects of stress ratio on FCG in an Al-alloy in the absence of closure and prediction of residual stress in Ti-6Al-4V generated by laser shock peening have been investigated.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1997
- Accession Number
- ADA370465
Entities
People
- Brian D. Worth
- Noel E. Ashbaugh
- Reji John
- W. J. Porter
Organizations
- University of Dayton