Fatigue of Materials

Deterioration in strength caused by heavy stre es applied for a long time or at frequent intervals. It has been shown that materials subject to repeated stre es exceeding the elastic limit will break after a large number of applications of stre , none of which approaches the static ultimate strength. In the case of steel, many phenomena of this cla are due to a further combination of the carbon with the iron as a result of local shocks in use, or maltreatment in manufacture. In filamentous or nodular materials like wrought-iron or other weld-metal, it comes from a disaggregation of the metal particles in their cinder envelopes, and a somewhat similar effect is noticed in metals of the copper cla . The reverse of fatigue is the refreshment of metals; which is the restoration of their original qualities to overstrained metals by rest or by heating. See CRYSTALLIZATION OF METALS.