Conditioning monitoring by microstructural evaluation of cumulative fatigue damage
- Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan). Research Labs.
- Electric Power Research Inst., Charlotte, NC (United States). O and M Cost Control Technology
- Pennsylvania State Univ., University Park, PA (United States). Coll. of Engineering
The objective of this work is to evaluate the damage induced below and above the fatigue limit ({Delta}{sigma}{sub t} = 360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue test bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 438549
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 27, Issue 12; Other Information: PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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