加工硬化した鋼材の疲労(第9報)

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The Ono type rotary bending fatigue limits are shown about three groups of specimens of 0.53% carbon steel. The first group of specimens, having circular groove of 1.0mm radius, were deformed by statical tensile or compressive stresses of 36.0 kg/mm^2 and 56.0kg/mm^2 beyond the yield point before bending fatigue test. The second group were deformed by statical uniform bending moment of about 3% maximum strain. The third group were deformed by statical torsional shear strain of 3%, 10% and 21%. These plastic deformations have produced the work hardening and the residual stress, and the effect of residual stress upon the fatigue limit is shown by comparing with the effect of the work hardening only in previous work (8th report). The experimental results are as follows : (1) The fatigue limit of notched specimens, pre-worked by tensile stress of 36.0kg/mm^2, rises by 6% as compared with the annealed state, and falls by 10% for compressive pre-working of the same degree. These results indicate that the fatigue limit increases by the residual compressive stress induced at the root of notch, and decreases by the residual tensil stress. Accordingly, the influence of the residual stress upon the fatigue limit is quite appreciable. (2) The fatigue tests on the notched specimens, pre-worked by large stress of 56.0kg/mm^2, indicate that the work hardening have a greater effect on the fatigue strength than the effect of residual stress. (3) The effect of residual stress upon the fatigue strength can not be found by the fatigue of specimens pre-worked by plastic bending. The fatigue fracture -is always due to the progressive spreading of fatigue crack started from bending tension side, that is, at side having the residual compressive stress. (4) Comparing with the annealed state, the fatigue limit obtained by specimens after plastically deformed by torsion falls about 8% for 3% shearing strain, and rises about 20% for large strain of about 21%. This tendency is similar to that obtained by specimens of the work hardening only (8th report). The effect of residual stress upon the fatigue limit can not be found. (5) The effect of residual stress upon the fatigue strength appears to depend on the mechanical property of material and constrained condition of the residual stress. The fatigue strength of the hard materials are affected appreciably by the residual stress.
宇宙航空研究開発機構の論文
1955-02-25

加工硬化した鋼材の疲労(第9報)

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