The purpose of this study was to determine the stress concentration factor in a shoulder under a cyclic tensile load. The test specimens were models of a propeller blade root section similar to the blade design now employed in the fans of the Cooperative Wind Tunnel. All specimens were given a 5 microinch finish and all were made of 76S-T aluminum alloy taken from an actual propeller blade forging. Two series of tests were conducted. One series consisted of a cyclic tensile load varying from zero to maximum over a nominal stress range from 21,000 psi to 28,000 psi. The other series consisted of a cyclic load, wherein the amplitude of the cyclic stress was varied from 20 to 50 percent of the maximum developed stress. These two conditions would correspond respectively to the "start-stop" cycle of wind tunnel operation and to constant speed tunnel operation.
It was found that the stress concentration factor determined from the fatigue test results closely approximated the results obtained from the three dimensional static tests of the actual blade.
This work was carried out by the authors at the Guggenheim Aeronautical Laboratory, California Institute of Technology, under the supervision of Dr. E. E. Sechler.
