Crack Tip Plasticity Associated with Corrosion Assisted Fatigue.
Annual rept. Jun 76-Jun 77,
SOUTHWEST RESEARCH INST SAN ANTONIO TEX
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The plasticity associated with propagation of a fatigue crack was found to be altered by a moist air environment, as compared to a dry nitrogen environment. Subcell size distribution and size of the plastic zone are the parameters altered, with the moist air causing a smaller plastic zone with the resulting redistribution of subcell sizes. The energy for crack propagation has been determined by the combination of subcell size and work per cycle required to give that subcell size. This calculation indicates a decrease of 67 in the energy for crack propagation is caused by the moist environment. The moist air environment also alters fracture surface features in a manner consistent with the plasticity results. Hydrogen is believed to be responsible for these changes, in that it can 1 make dislocation motion more difficult, and 2 decrease the strain to fracture. An effort was made to directly detect hydrogen by ion microprobe, but the results were inconclusive. Author
- Properties of Metals and Alloys