The Fatigue Strength of Large Single-Pinned and Double-Pinned Connections Made from Alloy Steel FV520B

Abstract

Fatigue tests have been conducted on single-pinned and double-pinned lugs made from alloy steel FV520B and loaded by means of 2 in diameter pins. The effects of pin fit for both clearance and interference and of various treatments were investigated. The treatments included side relieving the lug hole, bushing the bore, applying the Sulfinuz process to the lug or overstraining the lug bore. Two conditions of mean stress were investigated, namely, pulsating or repeated tension and 15 tons/in2mean tension.Basing comparison on the fatigue strength at 30 × 106cycles, the untreated lugs with close fit pins showed the lowest strength of all. Both clearance and interference fits were beneficial and by appropriate choice, the fatigue strength could be at least doubled and in some cases trebled. Lugs which had side relief, had been bushed, Sulfinuz treated or which had overstrained bores also gave worthwhile increases in fatigue strength and the strength ratios were generally in excess of 2.An increase in mean stress significantly reduced fatigue strength for all lugs tested, except for those with close fit or clearance fit pins.Comparing the present results with those obtained on lugs one-quarter the size, a considerable size effect is evident for some conditions, large lugs being weaker than small lugs.