Home > Fatigue (material)
In materials science, fatigue is a process by which a component is weakened by repeated bending or other cyclic stress, often to the point of fracture. The stress can be small enough to be below the ultimate tensile stress, or even the yield stress of the material. However, over a large number of cycles the effect can be catastrophic.
1 Characteristics of fatigue failures
The following characteristics are common to fatigue in all materials:
- The process starts with a microscopic crack, called the initiation site, which then widens with each subsequent movement, a phenomenon analysed in the topic of fracture mechanics.
- Failure is essentially probabilistic. The number of cycles required for failure varies between homogeneous material samples. Analysis demands the techniques of survival analysis.
- The greater the applied stress, the shorter the life.
- Damage is cumulative. Materials do not recover when rested.
- Fatigue life is influenced by a variety of factors, such as temperature and surface finish , in complicated ways.
- Some materials, for example steel and titanium, exhibit a fatigue limit, a limit below which repeated stress has no effect. Most others, for example aluminium, exhibit no such limit and even infinitesimally small stresses will eventually cause failure.
2 Timeline of fatigue history
- 1829: Wilhelm Albert first discusses the phenomenon on observing the failure of iron mine-hoist chains in Clausthal mines.
- 1839Events January 9 The French Academy of Sciences announces the Daguerreotype photography process. January 19 British East India Company captures Aden January 20 In the Battle of Yungay, Chile defeats a Peruvian and Bolivian alliance. February 24 William Ot: The term fatigue becomes current when Jean-Victor PonceletJean-Victor Poncelet ( July 1, 1788 December 22, 1867) was a mathematician and engineer who did much to revive projective geometry. Born to a poor family in Metz, France, Poncelet won a scholarship to the lycee and then the Ecole Polytechnique where he st describes metals as being tired in his lectures at the military school at MetzMetz is a city in the North-East of France, capital of the Lorraine region and of the departement of Moselle (57). It is located at the confluence of the Moselle and the Seille. History In ancient times Metz, then known as Divodurum, was the capital of th.
- 1843Events February 6 The first minstrel show in the United States The Virginia Minstrels opens (Bowery Amphitheatre in New York City). February 11 Giuseppe Verdi's opera I Lombardi premieres in Milan May 18 The Disruption of the Church of Scotland took place: William John Macquorn RankineWilliam John Macquorn Rankine ( July 2, 1820 December 24, 1872) was a Scottish engineer and physicist. He was a founding contributor to the science of thermodynamics. Rankine developed a fully complete theory of the steam engine. His steam engine manuals recognises the importance of stress concentrationA stress concentration is a phenomenon encounterered in mechanical engineering where an object under load has higher than average local stresses due to its shape. The types of shape that cause these concentrations are: cracks, sharp corners, holes and nar in his investigation of railroad axleAn axle is a central shaft for a rotating wheel or gear. In some cases the axle may be fixed in position with a bearing or bushing sitting inside the hole in the wheel or gear to allow the wheel or gear to rotate around the axle. In other cases the wheel failures following the Versailles accident.
- 1849: Eaton Hodgkinson is granted a small sum of money to report to the UK Parliament on his work in ascertaining by direct experiment, the effects of continued changes of load upon iron structures and to what extent they could be loaded without danger to their ultimate security.
- 1860: The first systematic investigations of fatigue life by Sir William Fairbairn and August Wöhler. Wöhler's study of railroad axles leads him to the idea of a fatigue limit and to propose the use of S-N curves in mechanical design.
- 1903: Sir James Alfred Ewing demonstrates the origin of fatigue failure in microscopic cracks.
- 1910: O. H. Basquin clarifies the shape of a typical S-N curve.
- 1939: Invention of the strain gauge at Baldwin-Lima-Hamilton catalyses fatigue research.
- 1945: A. M. Miner popularises A. Palmgren 's ( 1924) linear damage hypothesis as a practical design tool.
- 1954: L. F. Coffin and S. S. Manson explain fatigue crack-growth in terms of plastic strain in the tip of cracks.
- 1961: P. C. Paris proposes methods for predicting the rate of growth of individual fatigue cracks in the face of initial scepticism and popular defence of Miner's phenomenological approach.
- 1968: Tatsuo Endo and M. Matsuiski devise the rainflow-counting algorithm and enable the reliable application of Miner's rule to random loadings.
- 1970: W. Elber elucidates the mechanisms and importance of crack closure.
- 1975: S. Pearson observes that propagation of small cracks is sometimes surprisingly arrested in the early stages of growth.
