Actual and Predicted Fatigue Lives of D6AC Steel in Very Dry and Fully Water Saturated Air Environments.
Abstract
Under the four-load-range (standard) program loading sequence used in this investigation, the total fatigue lives in a fully water-saturated air environment were about 35% of those in very dry air. Other tests in which the two highest-load-range cycles in each program of 2594 cycles in the sequence were omitted (truncation) reduced the total fatigue lives by about 40% and 50% respectively in the wet and dry air environments. In wet air the crack initiation life under the standard program was about half that in dry air, and the propagation life to failure about one-third of that in dry air. The average crack propagation rate in wet air was up to three times faster than that in dry air. This indicates that the environment has a greater effect on the crack propagation phase than on the crack initiation phase of the fatigue process. Fatigue life predictions for the programmed loading cases were made using the constant-amplitude fatigue data and the simple Palmgren-Miner linear cumulative damage hypothesis. For both environments, the predicted program lives were less than the actual lives, the ratio predicted/actual being about 0.36 under dry air and about 0.33 under wet air conditions. Thus, under the particular sequence of loads and environments used, the predictive method was conservative.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1977
- Accession Number
- ADA060804
Entities
People
- D. S. Kemsley
- J. Y. Mann