Some Studies on the Rotating Bending Fatigue of Large Mild Steel Specimens : Part 3,Fatigue Strength and Crack Propagation in Specimens with Shoulder Fillet

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The authors have made two kinds of fatigue test on shoulder fillet specimens (one is 135 mm dia. at the testing part and 15,25 and 40 mm in fillet radius, the other is 14 mm dia. having proportional sizes to the large one), for the purpose of obtaining fatigue notch factors on shoulder fillet by comparing their fatigue limits with those of 125φmm and 10φmm plain cylindrical specimens described in Part 1. On the other hand, the stress concentration factors have been determined on fillets of the large specimens by taking into account the effect of the ratio of gauge length to fillet radius. Furthermore, the authors have studied the relationship between the stress and the propagating speed of fatigue crack by analysing shelly patterns on fracture surfaces of shoulder fillet specimens. It has been disclosed from these tests that ; (1) The correcting factors are 1.06,1.018 and 1.006 where the above ratios are 0.60,0.36 and 0.225,respectively. Stress concentration factors given by R.E. Peterson are equal to the author's ones without correction. (2) Fatigue notch factors of large specimens are nearly equal to those of smaller ones, and coincide with the corrected concentration factors of equivalent stress besed upon Mises'criterion. (3) Fatigue crack decreases remarkably its propagating speed as the stress concentration factor on the fillet part becomes larger.
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