Fatigue Strength of Threaded Steel Rods

摘要

An investigation was made to determine the fatigue strength of several types of threads suitable for use on 105 mm Howitzer Recoil Mechanism piston rods. Fatigue tests, which simulated the loading of the piston rods were conducted with 124 threaded specimens. The specimens were 1.125 and 1.250 inches diameter and had conventional UNF ground, large root radius UNJF ground, and large root radius UNJF rolled threads. Specimens of both sizes with large root radius rolled threads had an average of 34 percent greater fatigue strength than specimens with ground threads of the same profile. Specimens with large root radius ground threads had an average of 7 percent greater fatigue strength than those with conventional UNF ground threads. Considering all three types of threads, the 1.250 inch diameter specimens, with 27 percent more stress area, were only 9 percent stronger than the 1.125 inch diameter specimens. Limited tests at minus 65F showed that the fatigue strength of the specimens was greater at this temperature than at temperatures from 60 to 90 F. (Author)