A Feasibility Study for Verification of Fatigue Reliability Analysis
Final technical rept. 16 Mar-15 Jun 1970
BOEING CO RENTON WA COMMERCIAL AIRPLANE GROUP
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Experimental data have been developed and analyzed that provide some substantiation of the analytical concepts used in the fatigue reliability analysis previously performed. Extreme failure data were derived from constant- amplitude fatigue tests of large panels containing 300 identical and independent details, namely, circular holes. These tests simulate a fleet of separate details under controlled operation. Based on finite element analyses and photoelastic experiments, an acceptable panel configuration was determined, providing a virtually identical stress field around each hole of a large number of equally stressed holes. A Boeing-developed crack monitoring system, which uses conductive paint, detected the cracks when they reached 0.02 in. in length. This permitted the cracked holes to be reworked by oversizing and cold working such that the influence on the stress fields of surrounding holes was kept at a minimum. Estimates of the characteristic life and the log-average life were derived from constant-amplitude fatigue tests of small, single-hole specimens loaded under the same conditions as the large panels and showing a hole stress field identical to that in the large panel. These estimates were used to predict the median time to first failure in the large panel. The constant-amplitude fatigue tests establish the feasibility of testing single specimens with a large number of identically stressed details to examine the time-to-failure distribution characteristics of the population of details.
- Test Facilities, Equipment and Methods