Metal Fatigue and Basic Theoretical Models: A Review

TLDR: The concept of rotating-bending fatigue test was introduced by Wohler in this paper, which led to the development of stress-rpm (S-N) diagram for estimating fatigue life and endurance or fatigue limit of metal, the fatigue limit representing the stress level below which the component would have infinite or very high fatigue life.

Abstract: Preliminary understanding about fatigue failure of metals developed in 19th century during industrial revolution in Europe when heavy duty locomotives, boilers etc. failed under cyclic loads. It was William Albert who in 1837 first published an article on fatigue that established a correlation between cyclic load and durability of the metal. Two years later in 1839, Jean-Victor Poncelet, designer of cast iron axles for mill wheels, officially used the term fatigue for the first time in a book on mechanics. In 1842, one of the worst rail disasters of 19th century occurred near Versailles in which a locomotive broke an axle. Examination of broken axle by William John Macquorn Rankine from British railway vehicles showed that it had failed by brittle cracking across its diameter. Some pioneering work followed from August Wohler during 1860-1870 [1] when he investigated failure mechanism of locomotive axles by applying controlled load cycles. He introduced the concept of rotating-bending fatigue test that subsequently led to the development of stress-rpm (S-N) diagram for estimating fatigue life and endurance or fatigue limit of metal, the fatigue limit representing the stress level below which the component would have infinite or very high fatigue life. In 1886, Johann Bauschinger wrote the first paper on cyclic stress-strain behavior of materials. By the end of 19th century, Gerber and Goodman investigated the influence of mean stress on fatigue parameters and proposed simplified theories for fatigue life. Based on these theories, designers and engineers started to implement fatigue analysis in product development and were able to predict product life better than ever before. At the beginning of the 20th century, J. A. Ewing demonstrated the origin of fatigue failure in microscopic cracks. In 1910, O.H. Baskin defined the shape of a typical S-N curve by using Wohler's test data and proposed a log-log relationship. L. Bairstow followed by studying cyclic hardening and softening of metals under cyclic loads. Birth of fracture mechanics took place with the work of Alan A. Griffith in 1920 who investigated cracks in brittle glass. This promoted understanding of fatigue since concepts of fracture mechanics are essentially involved in fatigue crack characteristics. However, despite these developments, fatigue and fracture analysis was still not regularly practiced or implemented by the designers.