Effect of Non-Proportionality in the Fatigue Strength of 42CrMo4 Steel

Abstract:

The unexpected collapse of engineering structures is often caused by the fatigue phenomenon resulting from degradation of mechanical properties of materials due to multiaxial cyclic loadings. The interpretation of such degradation is a topic of intensive research in multiaxial fatigue. The fatigue strength is commonly evaluated by the equivalent stress based on the shear stress in the octahedral plane. However, the use of this kind of equivalent stress in the multiaxial fatigue criteria has been proven to be inappropriate. The degradation of mechanical properties of materials is dependent on several factors, e.g. the loading path has a strong influence on the fatigue strength. Non-proportional loadings cause higher damage in materials than proportional loadings for the same maximum equivalent stress. The purpose of this work is to study the effect of different multiaxial loadings on the 42CrMo4 steel and to improve the understanding about the relation between the fatigue strength and the sequential loading proportionality. The considered loadings were defined with the same history but with different load sequences and equivalent stress. To implement this work a biaxial servo-hydraulic fatigue machine was used. The fatigue life and crack angle were measured for each specimen. An analysis was made in order to correlate the crack initiation and fatigue life with the theoretical models, some remarks regarding these topics are presented.

• Periodical: Materials Science Forum (Volumes 730-732)
• Pages: 757-762
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.730-732.757
• Online since: November 2012
• Authors: Luís G. Reis, Vitor Anes, Bin Li, Manuel de Freitas
• Keywords: Fatigue Damage, Fractographic Analysis, Multiaxial Fatigue, Nonproportional Loadings

References

[1] Reis, L., Li, B., Freitas, M., "Evaluation of a Multiaxial Fatigue Models for a Structural Steel (42CrMo4)", proceedings of 8th Int. Conference on Multiaxial Fatigue & Fracture (2007).

[2] M de Freitas, L Reis and B. Li. Comparative study on biaxial low-cycle fatigue behaviour of three structural steels, Fatigue and Fracture of Engineering Materials and Structures, Vol. 29, (12), (2006) 992 – 999.

DOI: 10.1111/j.1460-2695.2006.01061.x

[3] L. Reis, B. Li and M. de Freitas. Analytical and experimental studies on fatigue crack path under complex multiaxial loading, Fatigue and Fracture of Engineering Materials and Structures, Vol. 29 (4), (2006) 281-289.

DOI: 10.1111/j.1460-2695.2006.01001.x

[4] L. Susmel, A simple and efficient numerical algorithm to determine the orientation of the critical plane in multiaxial fatigue problems, International Journal of Fatigue, Volume 32, Issue 11, (2010) 1875-1883.

DOI: 10.1016/j.ijfatigue.2010.05.004

[5] J. Araújo, A. Gonçalves, E. Mamiya, Multiaxial Fatigue: A Simple Stress Based Criterion for Hard Metals, International Journal of Fatigue, England, v. 27, (2005) 177-187.

DOI: 10.1016/j.ijfatigue.2004.05.006

[6] X. Chen, D. Jin and KS Kim Fatigue life prediction of type 304 stainless steel under sequential biaxial loading, I. J. of Fatigue, Vol 28, (2006) 289-299.

DOI: 10.1016/j.ijfatigue.2005.05.003

[7] M Robillard and G Cailletaud Directionally defined damage in multiaxial low-cycle fatigue experimental evidence and tentative modelling. In: Kussmaul K, McDiarmid D, Socie D, editors. Fatigue under biaxial and multiaxial loading, ESIS10. London: Mechanical engineering publications, (1991) 103-30.

DOI: 10.1016/s1566-1369(03)80023-7

[8] W. Zhang and KJ Miller, A study of cumulative fatigue damage under variable loading mode conditions. Fatigue Fract Eng Mater Struc. (1996) 229-239.

DOI: 10.1111/j.1460-2695.1996.tb00962.x

[9] S Harada and T Endo, On the validity of Miner´s rule under sequential loading of rotating bending and cyclic torsion. In: Kussmaul K, McDiarmid D, Socie D, editors. Fatigue under biaxial and multiaxial loading, ESIS10. London: Mechanical eng. publications, (1991)161-178.

[10] Temmel C, Karlsson B, Ingesten N. Fatigue anisotropy in cross-rolled, hardened medium carbon steel resulting from MnS inclusions. Metall Mater Trans A 2006 2995–3007.

DOI: 10.1007/s11661-006-0181-0

[11] Reis, L., "Comportamento Mecânico de Aços em Fadiga Multiaxial a Amplitude de Carga Constante e Síncrona", Universidade Técnica de Lisboa, Instituto Superior Técnico, Tese de Doutoramento, (2004).

[12] Murakami Y, Kodama S, Konuma S. Quantitative evaluation of effects of nonmetallic inclusions on fatigue strength of strength steels – parts I and II. Trans JSME 1988 299–307.

[13] Socie, D. F. and Marquis, G. B., Multiaxial Fatigue, Society of Automotive Engineers, Warrendale, 2000.