抄録
Using the values of deflections which can be measured easily during the rotatory bending fatigue test of a specimen, and considering also the stress distribution on the cross section of the specimen, the authors have devised a method to analize quantatively the plastic and quasi-elastic strain energies per cycle and their accumulation.
In this paper a report is made of the devised method as applied to fatigue tests of two kinds of carbon steels including different pearlite patches.
The main results obtained from the research are as follows:
(1) The pearlite patch not only causes structural changes by fatigue but prevents propagation of cracks.
(2) The change in quasi-elastic energy accumulation with the fatigue process can be expressed in Σqq=1(IRRAD.E)q=AqK up to the occurrence of micro-cracks on the surface of the steel specimen including gross patches and fracture of the specimen including fine patches.
(3) If the plastic strain energy accumulation is plotted against the number of cycles on a log-log paper, four nodal points appear dividing the process of fatigue in five stages. The second nodal point in the initial fatigue appears to have relation with the yield of materials. Then, a fine slip appears in the vicinity of second nodal point, a slip band at about third nodal point and a intrusion at about fourth nodal point. The energy quantities at the third and the fourth points were a constant to the respective point, independent of the stress amplitudes and of the pearlite patches. The energy quantity required for the fracture of specimen was a constant to each stress amplitude.
