Bending fatigue test

[ganesh]

A spring steel ( SAE 9260) with UTS of about 1000 MPa in quenched and tempered condition was fatigue tested in three point bending mode ( Span 120 mm) thickness 6 mm. ( 150 X 50 X 6 ) mm cube. Stress ratio 0.1 and frequency 10 Hz. No failure is seen up to 40 lakh cycles even at 2000 MPa max stress. Ultimately It failed at 2300 MPs peak stress ( R: 0.1) after 2-3.5 Lakh cycles.
How could the specimen sustain such high loads in bending fatigie ( Almost two times its tensile UTS)
Can any body suggest me the science behind this behavior

regards

Ganesh

[ganesh]

A spring steel ( SAE 9260) with UTS of about 1000 MPa in quenched and tempered condition was fatigue tested in three point bending mode ( Span 120 mm) thickness 6 mm. ( 150 X 50 X 6 ) mm cube. Stress ratio 0.1 and frequency 10 Hz. No failure is seen up to 40 lakh cycles even at 2000 MPa max stress. Ultimately It failed at 2300 MPa peak stress ( R: 0.1) after 2-3.5 Lakh cycles (4 specimens):
How could the specimen sustain such high loads in bending fatigie ( Almost two times its tensile UTS)
Can any body suggest me the science behind this behavior

regards

Ganesh

[PinkertonD]

I think I am seeing double?? Damn, I need new glasses. Beer glasses that is .