The Fatigue of Powder Metallurgy Alloys.
Final scientific rept. 1 Dec 80-30 Nov 84,
CONNECTICUT UNIV STORRS DEPT OF METALLURGY
Pagination or Media Count:
One of the important conditions in qualifying high strength powder metallurgy alloys is their resistance to fatigue crack propagation. The results of the present investigation indicate that the fatigue crack propagation resistance of high strength PM aluminum alloys is equivalent to that of a comparable ingot metallurgy alloy in the near-threshold region. The ingot alloy exhibits a slightly lower crack growth rate in the intermediate region. However the higher strength of the PM alloys 550 MPa YS, 600 MPa UTS as compared to the ingot alloy 450 MPa, 550 MPa results in a reduction of fracture toughness with the result that the crack growth rates at high Delta k levels are higher in the PM alloys. If exactly equivalent tensile properties were present in both PM and IM materials perhaps this difference would not occur since nothing characterizable as a defect was found in the PM alloys. A procedure for the analysis of the growth of short cracks from notches based upon crack closure considerations has also been formulated. Short crack behavior is important in establishing inspection intervals in retirement for cause applications, for example. The rate and extent at which crack closure develops in the wake of a newly formed crack can be used not only in the treatment of short crack behavior, but also to account for the notch size effect in fatigue as well as for fatigue notch sensitivity.
- Metallurgy and Metallography