段付き丸棒のねじり疲労寸法効果について

Abstract

Some torsional fatigue tests were carried out to obtain the fundamental data of the fatigue notch effect and the fatigue size effect on the large steel shaft with shoulder fillet.Two kinds of materials were used for the tests. They were 0.37% carbon forged steel and chromium molybdenum forged steel, and their chemical compositions and mechanical properties are shown in Table 1 and Table 2. The working sections of the specimens are 50mm in diameter for the large shafts, and 7mm for the conventional small specimens, the forms and dimensions are shown in Fig. 1 and Table 3.As the tests results, the following aspects were obtained.(1) Good agreement was observed between the measured stress concentration factor α' (by means of electric resistance wire strain gauge) at fillet radii on large shafts and α presented by Peterson excepting a case of 1.5mm in fillet radius.(2) The fatigue limit strengths at 107 cycle are shown in Table 4. On the size effects, the reduction of the fatigue strength of 50∅ straight shaft compared with that of 7∅ was 13.5% for carbon steel, and 22% for chromium molybdenum steel. In case of the specimen with shoulder fillet, the reduction was 17% for carbon steel, and 13% for chromium molybdenum steel when α was about 1.5.(3) The reduction between the fatigue notch factor β2 (based on 7∅ straight shafts) and the stress concentration factor α is shown in Fig. 3. From this figure it seems that β2 is considerably smaller than α in case of carbon steel.(4) From the diagram of η (the fatigue notch sensitivity factor) plotted against notch radius as shown in Fig. 5, it seems that η of annealed carbon steel falls considerably lower than the average curve presented by Peterson.