Griffith’s Equation

Abstract

Most materials fracture suddenly because they contain small internal and surface cracks, which propagate under an applied stress. Griffith’s equation shows how fracture strength depends inversely on the square root of the size of the largest crack. It was developed by Alan Griffith, while he was working as an engineer at Royal Aircraft Establishment Farnborough just after the First World War. This chapter examines brittle and ductile fracture, the concepts of fracture toughness, stress intensity factor and stBiographical Memoirs of Fellows ofrain energy release rate, the different fracture modes, and the use of fractography to understand the causes of fracture in broken components. The importance of fracture mechanics was recognised after the Second World War, following the disastrous failures of the Liberty ships from weld cracks, and the Comet airplanes from sharp window corner cracks. Griffith’s father was a larger-than-life buccaneering explorer, poet, journalist and science fiction writer, and Griffith lived an unconventional, peripatetic and impoverished early life. He became a senior engineer working for the UK Ministry of Defence and then Rolls-Royce Aeroengines, famously turning down Whittle’s first proposed jet engine just before the Second World War as unworkable because the engine material would melt, then playing a major role in jet engine development after the war, including engines for the first vertical take-off planes.