ABSTRACT
In the 17th century, the great scientist and painter, Leonardo da Vinci, performed some strength measurements on piano wire of different lengths. Somewhat surprisingly, he found that the strength of piano wire decreased with increasing length of wire. This length-scale dependence of strength was not understood until the 20th century when the serious study of fracture was revisited by a number of investigators. During the first quarter of the 20th century, Inglis (1913) showed that notches can act as stress concentrators. Griffith (1921) extended the work of Inglis by deriving an expression for the prediction of the brittle stress in glass. Using thermodynamic arguments, and the concept of notch concentration factors from Inglis (1913), he obtained a condition for unstable crack growth in brittle materials such as glass. However, Griffith’s work neglected the potentially significant effects of plasticity, which were considered in subsequent work by Orowan (1950).
