University of Illinois Engineering Experiment Station. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
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
