Abstract
We studied the effects of the speed of cyclic stressing and the shape of notches on the time-strength of 0.5per sent carbon steel by means of Ono's rotating beam fatigue machine. Unnotched specimens, notched specimens with circumferential semicircular groove and with circumferential 60deg V-shaped groove were tested at 1700 and 63rpm respectively. Rotating-beam fatigue tests were mainly run at 6 different nominal stresses from 80 to 40kg/mm2, which were greater than the yield point of the material as found under static tension. We used 5 specimens at each stress level.
Summary of the results is as follows:
(1) In notch tests, the average value of the fatigue life of 5 specimens at 63rpm is 25 to 14per sent less than that at 1700rpm and all the test results have fallen within the individual scatter band of the fatigue life, indicating the apparent effect of testing speed.
(2) However, in unnotch tests, probably attributing to harmful internal heating, the test results both at 1700 and 63rpm are almost fallen within the same scatter band, indicating no apparent effects of testing speed.
(3) Below about 65kg/mm2, the fatigue life decreases as the stress concentration factor becomes greater. However, above 65kg/mm2, the fatigue life of the semicircular notched specimens becomes greater than that of the unnotched specimens. Hence it appears that the effect of notches on the time-strength may not always be harmful.
