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Sequenced Axial and Torsional Cumulative Fatigue: ... 181

early growth and may therefore predict cumulative damage accumulation where observable
cracking does not appear until late in the cyclic life. However, methods based on crack
propagation arguments would seem to be more likely to produce good correlations where
significant cracking develops early in life. Some method of transitioning between these
regimes is required for reliable estimates of Cumulative fatigue damage under complex loading
conditions.

CONCLUSIONS
The following conclusions are drawn from this study of the cumulative fatigue behavior of
Haynes 188 at 538°C:
1) Neither the LDA nor the DCA have predicted the interactions in these experiments
particularly well. Predictions by the LDA have been generally conservative (under
predicted life), whereas the DCA predictions have been generally non-conservative (over
predicted life).
2) There appears to be a transition that occurs at or about an initially imposed life fraction of
0.4 in the set of experiments conducted. Below this level the material adheres to a linear
damage rule. Above this level, the damage accumulation appears to be non-linear.
3) The fatigue life data indicate a transition behavior that is linked to the extent of work
hardening imposed by the initial load level: the greater the life fraction expended in lower
amplitude loading, the greater the chance of having a sum of life fractions more than unity.
4) The stabilized (half-life) stress response in the second load level does not show any
correlation with damage accumulation for the loading conditions imposed.

REFERENCES

1. Kalluri, S. and Bonacuse, P. J. (2000), “Cumulative Axial and Torsional Fatigue: An
Investigation of Load-Type Sequencing Effects,” In: STP 1387 -- Multiaxial Fatigue and
Deformation: Testing and Prediction, pp. 281-301, S. Kalluri and P. J. Bonacuse (Eds),
ASTM, West Conshohocken, PA.
2. Miner, M. A. (1945), “Cumulative Damage in Fatigue,” Journal ofApplied Mechanics 12,
No. 3, (Trans. ASME, Vol. 67), pp. A159-A164.
3. Manson, S. S. and Halford, G. R. (1981), “Practical Implementation of the Double Linear
Damage Rule and Damage Curve Approach for Treating Cumulative Fatigue Damage,”
Int. J. Fracture 17, pp. 169-192.
4. Bui-Quoc, T., (1982), “Cumulative Damage with Interaction Effect due to Fatigue Under
Torsion Loading,” Experimental Mechanics, pp. 180- 187.
5. McGaw, M. A., et al., (1993). “The Cumulative Fatigue Damage Behavior of Mar-M 247
in Air and High Pressure Hydrogen,” In: ASTM STP 1211, Advances in Fatigue Lqetime
Predictive Techniques: Second Volume, pp. 117-131, M. R. Mitchell and R. W. Landgraf,
(Eds.), ASTM.
6. Halford, G. R., (1997), “Cumulative fatigue damage modeling - crack nucleation and early
growth,” Int. J. Fatigue 19, Supp. No. 1, pp. S253-S260.