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PEM5139 - Fatigue of Metallic Materials

Form professor

Prof. Dr. Carlos Antonio Reis Pereira Baptista

Workload

Theoretical	Practical	Study	Duration	Total	Credits
4 hours/week	0 hours/week	8 hours/week	15 weeks	180 hours	12

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Concentration area

97135 - Conventional and Advanced Materials

Objectives

To introduce the fundamentals of the mechanical behavior of metallic materials subjected to cyclic loadings. To develop analytical methods of fatigue design and life prediction. To discuss the recent advances in this field related to testing methodologies, data analysis and modeling, as well as materials processing technologies.

Motivation

It is widely acknowledged that fatigue is the main cause of in-service failure of components and structures. Therefore, it is very important to the materials scientists and engineers to understand the process of damage evolution under specific loading conditions, until the final failure. Despite having been one of the main research subjects of materials science during the last century, the research in metal fatigue has not diminished in importance; instead is increasingly attracting attention due to the challenges introduced by the use of new alloys, experimental techniques and increased computational capacity.

Syllabus

1. Preliminary considerations: Historical background, characterization of cyclic loadings, mechanical behavior, cyclic plastic deformation, crack nucleation and propagation, macroscopic and microscopic aspects of fatigue, specimens and testing machines, fatigue design criteria.
2. Stress-life relationships: S/N curves, mean stress effects, statistical aspects, fatigue damage, cycle counting methods, very-high cycle fatigue, factors affecting S/N curves, multiaxial stresses.
3. Low-cycle fatigue: The Coffin-Manson approach, strain-controlled fatigue tests, cyclic mechanical properties of materials, hysteresis loops and internal hardening variables, effect of cycle asymmetry, multiaxial loading, life estimation of structural components.
4. Fatigue Crack Growth: Fundamentals of linear elastic fracture mechanics, monotonic and cyclic plastic zones, da/dN-ΔK curves, stress ratio (R) effects, Elber’s concept of crack closure, methods for closure measurement, two-parameter models of fatigue crack propagation. The Unified Approach, predictive methods, variable amplitude loadings (load spectra), overload effects.
5. High-temperature fatigue: Thermal fatigue, isothermal fatigue, in-phase and out-of-phase thermo-mechanical fatigue, creep-fatigue interaction: high-temperature strain-controlled tests with dwell-time, metallurgical effects: dynamic strain hardening.
6. Factors affecting fatigue behavior: influence of frequency, surface finishing, environment, notch effects, residual stresses, stress relaxation. Influence of microstructure on fatigue behavior of steels, aluminum alloys and titanium alloys. Fatigue of welds. Fatigue of ultra-fine grained and nano-crystalline materials.

Evaluation criteria

1. Series of exercises.
2. Group works (reports and seminars).
3. Final Exam.

References

1. R.I. STEPHENS, A. FATEMI, R.R. STEPHENS, H.O. FUCHS. Metal Fatigue in Engineering. New York: John Wiley. Second Edition, 2001, 472p.
2. M. KLESNIL, P. LUKÁŠ. Materials Science Monographs 71: Fatigue of Metallic Materials. Amsterdam: Elsevier. Second Edition, 1992, 270p.
3. Y. LEE, J. PAN, R. HATHAWAY, M. BARKEY. Fatigue Testing and Analysis: Theory and Practice. Amserdam: Elsevier, 2005, 402p.
4. S. SURESH. Fatigue of Materials. Cambridge University Press, Second Edition, 2001, 679p.
5. D.R. SOCIE, G.B. MARQUIS. Multiaxial Fatigue. Warrendale: SAE International, 2000, 484p.
6. L. MOLENT, S.A. BARBER, R.J.H. WANHILL. The Lead Crack Fatigue Lifing Framework. DSTO-RR-0353, Defence Science and Technology Organisation (Austrália), 2010, 58p.
7. N.E. DOWLING. Mechanical Behavior of Materials. New Jersey: Prentice Hall. Third Edition, 2006, 936p.
8. J.T.P. CASTRO, M.A. MEGGIOLARO Fadiga - Técnicas e Práticas de Dimensionamento Estrutural sob Cargas Reais de Serviço: Vol. I – Iniciação de Trincas (Portuguese Edition). Createspace Books, 2009, 494p.
9. J.T.P. CASTRO, M.A. MEGGIOLARO Fadiga - Técnicas e Práticas de Dimensionamento Estrutural sob Cargas Reais de Serviço: Vol. II – Propagação de Trincas, Efeitos Térmicos e Estocásticos (Portuguese Edition). reatespace Books, 2009, 578p.
10. L. MOLENT, Q. SUN, A.J. GREEN Characterization of equivalent initial flaw sizes in 7050 aluminum alloy. Fatigue and Fracture of Engineering Materials and Structures, Blackwell Publishing, 2006, 22p.
11. L. MOLENT, S.A. BARBER, R.J.H. WANHILL. The Lead Crack Fatigue Lifing Framework. International Journal of Fatigue, v.33, p.323-331, 2011.
12. W. ZHUANG, L. MOLENT Analytical study of fatigue crack growth in AA7050 notched specimens under spectrum loading. Engineering Fracture Mechanics, v.77, p.1884-1895, 2010,
13. P. LUKÁŠ, L. KUNZ, P. HUTAŘ (Editors). Proceedings of 10th International Fatigue Congress. Prague, Czech Republic. Published in: Procedia Engineering, Elsevier, 2010.
14. W.S. JOHNSON (Editor). Proceedings of 9th International Fatigue Congress. Atlanta, United States. Published in cd-rom by Elsevier, 2006.
15. A.F. Blom (Editor). Proceedings of 8th International Fatigue Congress. Stockholm, Sweden. Published by EMAS Books, vols. 1-5, 2002.