An investigation into cold dwell fatigue behaviour in Ti6246 and other aerospace alloys

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Whittaker, Richard James (2011). An investigation into cold dwell fatigue behaviour in Ti6246 and other aerospace alloys. University of Birmingham. Eng.D.

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Abstract

The susceptibility of Ti6246 to cold dwell fatigue behaviour has been assessed as part of a wider investigation into the relationship between optical microstructure, crystallographic texture, mechanical behaviour and material processing for various common titanium aerospace alloys.
Assessment of the full range of production microstructures for Ti6246 has shown acceptable maximum texture intensities and crystallographic unit size variations. Debit on cold dwell fatigue life has only been observed at very high proportions of the ultimate tensile strength of the material. Heat treatment to eliminate potential ‘good’ factors in the dwell response of conventional microstructures was also noted not to produce a large cold dwell fatigue life debit. The absence of dwell effects may be attributed to one or more factors, including susceptibility of large colony microstructures to other failure modes to the extent that they are activated before the mechanism leading to cold dwell fatigue facet formation.
Characterisation of optical microstructures and textures has revealed a range of structures associated with different titanium alloys and product forms. It has been noted that common crystallographic features may be observed in very different microstructures in these alloys. It is concluded from this work that the optical microstructure should not be taken as an accurate indication of the effective structural unit size in titanium alloys.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

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