An investigation into the multiaxial fatigue behavior of IMI 829 titanium alloy
This document studies the effect that multiaxial stress fields have on the fatigue behavior of IMI 829 titanium alloy, a material often used for compressor disks in gas turbine engines. Experimentation in this study has included the cyclic testing of rotating disk specimens of varying geometries as well as ASTM E-647 crack growth testing employing standard compact tension specimens. Fractographic and microstructural examinations were also conducted. It was observed that the disk specimens demonstrated lower crack growth rates for a given stress intensity range than did the compact tension specimens. This behavior was explained by considering the effect of the multiaxial stress field on the crack tip opening displacement. Any loads parallel to a given crack will effectively reduce the crack tip opening displacement due to the Poisson effect, resulting in a smaller crack tip plastic zone which has been previously related to crack growth rate. Fractographic examination of the disk and compact tension specimens indicated that the disk specimens were much more likely to form striations than did the compact tension specimens. This was explained by the fact that the test conditions differed between the disk and compact tension specimens. Due to mechanical limitations, the cyclic frequency of the disk specimens was considerably lower than the cyclic frequency of the compact tension tests. Differences in test temperature may also have influenced the change in fracture surface between the specimens. The effect that microstructure had on the fatigue crack growth in the disk specimens was investigated as well. It was observed that crack generally followed a transgranular path. It was also noted that when possible, the crack would attempt to cross prior beta grain boundaries at right angles. The existence of grain boundary aligned alpha was found to influence this behavior.
- Research Organization:
- Utah Univ., Salt Lake City, UT (United States)
- OSTI ID:
- 6465955
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
33 ADVANCED PROPULSION SYSTEMS
GAS TURBINE ENGINES
FATIGUE
TITANIUM ALLOYS
CRACK PROPAGATION
GRAIN BOUNDARIES
CRACKS
FRACTOGRAPHY
FRACTURING
MICROSTRUCTURE
STRESS INTENSITY FACTORS
ALLOYS
ENGINES
HEAT ENGINES
INTERNAL COMBUSTION ENGINES
MECHANICAL PROPERTIES
360103* - Metals & Alloys- Mechanical Properties
330103 - Internal Combustion Engines- Turbine