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

Fatigue Behavior of Axially Loaded Weldments in HY-80 Steel

Bureau of Ships, U.S. Navy.Contract NObs 77137Index No. NS-021-20

Effect of Welding on the Axial Fatigue Properties of High Strength Structural Steels

The effect of welding on the axial fatigue properties of a quenched and tempered steel in the life range between 100,000 and 2,000,000 cycles has been investigated on a zero-to-tension and partial tension-to-tension stress cycle. Included in the studies are the effect of surface geometry and the metallurgical changes imparted by the welding. The test results indicate that the introduction of a transverse butt weld in this steel decreases the fatigue strength corresponding to 2,000,000 cycles by approximately 40 percent. On a zero-to-tension stress cycle, no significant increase has been found in the fatigue strength of welds in the quenched and tempered steel over comparable welds in ASTH A-7 or A-242 steels. The quenched and tempered steel has also been found to be more notch sensitive in fatigue and highly susceptible to even the most minor internal discontinuities. The data indicate that the superiority of the quenched and tempered steel lies in its ability to resist high mean stresses and is thus eminently suited for applications where high dead to live lead ratios are encountered.The Engineering FoundationAmerican Iron and Steel InstituteChicago Bridge and Iron FoundationThe Welding Research Counci