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Estimation of the Fatigue Life of High Strength Steel  Under ._.   195

             After determination of the damage degree at an observation time To according to Eqs (38)
          and (39), we calculated the fatigue life (stage 8)






          or if we have time observation in blocks, we obtain calculated fatigue life in number of blocks
          Nb,cal





          where S (Nb)  is the damage degree accumulated in a single block of Nb cycles.
          Then the calculated number of cycles is equal to







          COMPARISON OF THE CALCULATED AND ACTUAL FATIGUE LIVES

          In  order  to  assess  the  algorithm  for  fatigue  life  calculation  under  proportional  variable-
          amplitude tension with torsion, presented in Fig.4, we must verify particular assumptions of
          that algorithm. At first we should verify the algorithm for constant amplitude loading. From the
          constants of the regression model for torsion, Eq. (2) and from Eqs (10) and (1 1)  we obtain
          bt = -0.066 and z'~ 937 MPa.
                        =
            Table  2 shows the fatigue lives under constant amplitude torsion calculated according to
          Eq.(41). The calculated and experimental fatigue lives are also compared in Fig5 From Table
          2 and Fig. 5 it appears that the proposed model gives correct results of the fatigue life calcula-
          tions for pure torsion. All the resuits are in the scatter band of the factor 3.

            Table 2. Calculated and experimental fatigue lives under constant amplitude torsion


                          'Tat     Neal               Nexp
                        [MPaI     [cycle]             [cycle]
                         450       27854           33000,35000
                         430       53326              60000
                         400      149842          130000,280000
                         370      456377      390000,600000,1100000
                         350      1009463         700000,900000
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