This paper reports the results of rotating cantilever-bending fatigue tests made on shafts having different size fillets connecting a 5 1/4-in-diam portion to a 6 9/16-in. section. These shafts were machined from normalized and tempered forgings of plain carbon steel of 0.52 per cent carbon content, conforming to S.A.E. 1050 steel. Ten shafts having polished fillets of 27/32 or 9/32 in. radius were tested to determine allowable design fatigue strength on the basis of 30,000,000 revolutions. Also seven shafts were tested having 9/32-in. fillets which were rolled with a single-roller burnishing tool. The endurance limit for the 27/32-in. polished fillet was found to be 25,500 psi, as compared with 18,500 psi for the 9/32 in. fillet. Rolling the 9/32 in. radius increased this value to 24,000 psi or an increase of 30 per cent over the not-rolled fillet. A comparison is also made between the results obtained on small specimens by other investigators with those on the larger members reported here.

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