Effect of Notches on the Axial Fatigue Properties of Structural Steels

The effect of the stress concentration on the zero-to-tension axial fatigue strength of notched members of four structural steels has been studied. For each of the four steels a critical notch severity was found at which a transition in behavior takes place. When the theoretical stress concentration exceeds this critical value the fatigue strength increases instead of continuing to decrease as would normally be expected. The maximum effective stress concentration determined from these tests corresponds to a critical notch severity which is dependent on the material) the geometry of the specimen) and the cyclic conditions of stress. Microscopic examinations of the roots of the notched specimens which did not fail revealed cracking in most cases. Some of the cracks apparently were nonpropagating cracks but the test lives in most cases were insufficient to isolate such cracks positively as non-propagating. A study of other data on non-propagating cracks revealed that the laws governing their formation are not yet fully understood. However, there are indications that the increase in fatigue strength obtained above the critical notch severity is coincident with the formation of non~propagating cracks.The Engineering FoundationAmerican Iron and Steel InstituteChicago Bridge and Iron FoundationThe Welding Research Counci