Page 453 - Biaxial Multiaxial Fatigue and Fracture

A Damage Model for Estimating Low Cycle Fatigue Lives Under Nonproportional Multiaxial Loading 437

become the appropriate model for LCF life prediction under complex nonproportional straining.
In Fig9 (b) where the life prediction is made by ASME strain instead of the nonproportional
strain parameter, some of the data under nonproportional straining are obviously underestimated
by more than a factor of two. The larger scattering of the data can be seen for the largerfNp tests,
such as Case 10, 12 and 14. The maximum scattering of the data almost reached a factor of 20.
In the data correlation for S45C. on the other hand, several data are correlated too
conservatively and the scattering of the data tends to be larger with increasing fatigue life. The
longer fatigue lives in the experiments can bee seen in the results of pure cyclic torsion tests.
Conservative life estimation in pure torsion tests under a constant Mises’ equivalent strain
condition were also reported for 304SS cruciform specimen C20j and tube specimen subjected to
tension/torsion [21].

CONCLUSION

This paper developed a simple damage model for the evaluation of LCF lives under complex
biaxial/multiaxial loadings. This model was developed by combining the equivalent strain,
based on the maximum principal strain, as the nonproportional LCF strain parameter with
Miner’s law. The model was able to correlate most of all the fatigue data for different materials
within a factor of two scatter band and was demonstrated to be effective for the nonproportional
LCF data correlations of various materials.

REFERENCES

1. ASME Code Case N-47 (1978), Case of ASME Boiler and Pressure Vessel Code, Case N-47,
Class 1, Section 3, Division 1.
2. Nitta A., Ogata T. and Kuwabara K. (1987), The Effect of Axial-Torsional Strain Phase on
Elevated-Temperature Biaxial Low-Cycle Fatigue Life in SUS304 Stainless Steel, J. Society
of Materials Science, Japan, 36,376. (Japanese).
3. Socie D. F. (1987), Multiaxial Fatigue Damage Models, ASME J. of Engng. Mater. Tech.,
109,293.
4. Itoh T, Sakane M, Ohnami M. and Socie D. F. (1995), Nonproportional Low Cycle Fatigue
Criterion for Type 304 Stainless Steel, ASME J. of Engng. Mater. Tech., 117,285.
5. Hamada N. and Sakane M. (1997), High Temperature Nonproportional Low Cycle Fatigue
Using Fifteen Loading Paths, Proc. of 5th Inf. Con. on Biaxial/ Multiaxial Fatigue and
Fructure, I, 25 1.
6. Wang C. H. and Brown M. W. (1993), A Path-Independent Parameter for Fatigue Under
Proportional and Non-proportional Loading, Fatigue and Fract. Engng. Mater. Sfruct., 16,
1285.
7. Chen X, Xu S. and Huang D. (1999), A Critical Plane-Strain Energy Density Criterion for
Multiaxial Low-Cycle Fatigue Life under Nonproportional Loading, Fatigue Fract. Engng.
Mater. Srruct., 22,679.