Metal fatigue is the process of gradual accumulation of microscopic damages in the metal structure under the influence of external factors, which further progress into larger and larger ones. This is a frequent occurrence that can lead to very disastrous results.
Detection and description of the phenomenon
The pioneer of the phenomenon was the German mining engineer Wilhelm Albert, who in 1829 described the wear of metal based on the results of his experiments using the example of repeated bends in the links of the chains of mine hoists on an experimental machine he had developed. However, the term "metal fatigue" was introduced only in 1839 by the French scientist Jean-Victor Poncelet, who described the decrease in the strength of steel structures under the influence of cyclic stresses.
A little later, the German engineer August Wöller made a contribution to the theory of metal fatigue, as well as the design of metal structures subjected to cyclic stresses, publishing in 1858-1870 the results of experiments with iron and steel under conditions of repeated tension-compression. The results of his research in 1874 were graphically presented in the form of tables by the German architect Lewis Spangenberg. Since then, a visual representation of the obtained relationship between the amplitudes of the cycle stress and the number of cycles before the destruction of the metal structure is called the Völler diagram.
Since then, the phenomenon of metal fatigue has received its clear definition as a process of accumulation over time of damage to a metal structure under the action of alternating (usually cyclic) stresses, which lead to a change in the properties of the structure, the formation of cracks in it, their progressive development and subsequent destruction of the material.
Consequences of metal fatigue
Progressive metal fatigue can lead to the destruction of metal structures. As a rule, this happens during their operation (when the maximum load on the mechanisms is carried out), which can lead to accidents and disasters, including with human casualties. Examples of some of the most famous incidents:
- the Versailles railway disaster in 1842, as a result of which 55 people died (the cause was a fatigue fracture of the locomotive axis).
- the crash of the high-speed electric train ICE near the Eschede commune in Germany in 1998, as a result of which 101 people died and 88 were injured (at a speed of 200 km / h, the wheel tire burst on the train).
- an accident at the Sayano-Shushenskaya HPP in 2009 (the cause was fatigue damage to the mounting points of the hydroelectric unit of the station, including the turbine cover).
Metal fatigue prevention
Metal fatigue is usually prevented by modifying parts of the metal structure to avoid cyclic loading, or by replacing the materials used in the structure with less fatigue-prone materials. Also, a noticeable increase in the endurance of the structure is provided by some methods of chemical-thermal treatment of metals (nitriding, nitrocarburizing, etc.). Another method of preventing metal fatigue is thermal spraying, which creates a compressive stress on the surface of the material, which helps to protect metal parts from fracture.
