Page 211 - Biaxial Multiaxial Fatigue and Fracture
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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