Alan Arnold Griffith (b 13 June 1893 - 13 Oct 1963) was a British engineer, who, among many other contributions, is best known for his work on stress and fracture in metals that is now known as metal fatigue, as well as being one of the first to develop a strong theoretical basis for the jet engine. June 13 is the 164th day of the year in the Gregorian calendar (165th in leap years), with 201 days remaining. ... 1893 was a common year starting on Sunday (see link for calendar). ... October 13 is the 286th day of the year (287th in leap years). ... 1963 was a common year starting on Tuesday (link will take you to calendar). ... In materials science, fatigue is a process by which a material is weakened by cyclic loading. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ...

Griffith took a first in mechanical engineering, followed by a Master’s Degree and a Doctorate from Liverpool University. In 1915 he was accepted by the Royal Aircraft Factory as a trainee, before joining the Physics and Instrument Department the following year in what was now been renamed as the Royal Aircraft Establishment (RAE). The University of Liverpool is a university in the city of Liverpool in the United Kingdom. ... 1915 was a common year starting on Friday (see link for calendar). ... This article needs cleanup. ... This article needs cleanup. ...

Some of Griffith's earlier works remain in widespread use today. In 1917 he and G.I.Taylor suggested the use of soap films as a way of studying stress problems. Using this method a soap bubble is stretched out between several strings representing the edges of the object under study, and the coloration of the film shows the patterns of stress. This method, and similar ones, were used well into the 1990s when computer power became generally available that could do the same experiment numerically. 1917 was a common year starting on Monday (see link for calendar). ... // Events and trends The 1990s are generally classified as having moved slightly away from the more conservative 1980s, but keeping the same mind-set. ...

Griffith is more famous for a theoretical study on the nature of stress and failure in metals. At the time it was generally taken that the strength of a material was E/10, where E was the Young's modulus for that material. However it was well known that those materials would often fail at 1000 times less than this predicted value. Griffith discovered that there were many microscopic cracks in every material, and hypothesized that these cracks lowered the overall strength of the material. This was because any void in a solid concentrates strain, a fact already well known to machinists at the time. This concentration would allow the strain to reach E/10 at the head of the crack long before it would seem to for the material as a whole. In solid mechanics, Youngs modulus (also known as the modulus of elasticity or elastic modulus) is a measure of the stiffness of a given material. ...

From this work Griffith formulated his own theory of brittle fracture, using elastic strain energy concepts. His theory described the behavior of crack propagation of an elliptical nature by considering the energy involved. The equation basically states that when a crack is able to propagate enough to fracture a material, that the gain in the surface energy is equal to the loss of strain energy, and is considered to be the primary equation to describe brittle fracture. Because the strain energy released is directly proportional to the square of the crack length, it is only when the crack is relatively short that its energy requirement for propagation exceeds the strain energy available to it. Beyond the critical Griffith crack length, the crack becomes dangerous.

The work, published in 1920, resulted in sweeping changes in many industries. Suddenly the "hardening" of materials due to processes such as cold-rolling were no longer mysterious. Aircraft designs immediately understood why their designs failed unless they were built much stronger than it seemed they should, and soon turned to polishing their metals in order to remove cracks. The result was a series of particularly beautiful designs in the 1930s, such as the Boeing 247. This work was later generalized by G. R. Irwin, in the 1950s, applying it to almost all materials, not just rigid ones. 1920 is a leap year starting on Thursday (link will take you to calendar) // Events January January 7 - Forces of Russian White admiral Kolchak surrender in Krasnoyarsk. ... // Events and trends The 1930s were spent struggling for a solution to the global depression. ... Boeing 247 The Boeing 247 was one of the first modern passenger airliners. ... Millennia: 1st millennium - 2nd millennium - 3rd millennium // Events and trends The 1950s in Western society was marked with a sharp rise in the economy for the first time in almost 30 years and return to the 1920s-type consumer society built on credit and boom-times, as well as the...

In 1926 he published a seminal paper, An Aerodynamic Theory of Turbine Design. He demonstrated that existing turbines were designed incorrectly and the blades were "flying stalled", proposing a modern airfoil shape for the blades that would dramatically improve performance. The paper went on to describe an engine using an axial compressor and two-stage turbine, the first stage driving the compressor, the second a power-take-off shaft that would be used to power a propeller. In modern terms he described a turboprop engine. As a result of the paper, the Aeronautical Research Committee supported a small-scale experiment with a single-stage axial compressor and single-stage axial turbine. Work was completed in 1928 with a working testbed design, but for some reason at that point work stopped. 1926 was a common year starting on Friday (link will take you to calendar). ... A diagram showing how a turboprop works. ... The Aeronautical Research Committee was a UK government committee established in 1919 in order to coordinate aeronautical research and education following World War I. Its scope was both military and civil applications. ... 1928 was a leap year starting on Sunday (link will take you to calendar). ...

At about this time Frank Whittle wrote his thesis on turbine engines, using a centrifugal compressor and single-stage turbine, the leftover power in the exhaust being used to power the aircraft directly. Whittle sent his paper to the Air Ministry in 1930, who passed it on to Griffith for comment. After pointing out an error in Whittle's calculations, he stated that the large frontal size of the compressor would be it unacceptable for aircraft use, and that the exhaust itself would provide little thrust. The Air Ministry replied to Whittle saying they were not interested in the design. Whittle was crestfallen, but was convinced by Johnny Johnson to pursue the idea anyway. Luckily for all involved, Whittle patented his design in 1930 and was able to start Power Jets in 1935 to develop it. Frank Whittle speaking to employees of NASA Glenn Research Center, USA, in 1946 Sir Frank Whittle (June 1, 1907 - August 9, 1996) was a Royal Air Force officer who invented the jet engine. ... Also called a radial blower, squirrel cage, or squirrel wheel compressor, a centrifugal compressor consists of an axle to which is mounted a cylindrical assembly of compressor blades. ... The Air Ministry was formerly a department of the United Kingdom Government, established in 1918 with the responsibility of managing the affairs of the (then newly formed) Royal Air Force. ... 1930 is a common year starting on Wednesday. ... Johnnie Johnson (born July 8, 1924) is a Rock and Roll Hall of Fame member, piano player and blues musician. ... 1930 is a common year starting on Wednesday. ...

Griffith moved to became the principal scientific officer in charge of the new Air Ministry Laboratory in South Kensington. There he evolved the contraflow gas turbine design, which used two sets of compressor disks rotating in opposite directions, one "inside" the other. This is as opposed to the more normal design in which the compressors blow the air against a stator, essentially a non-moving compressor disk. The effect on compression efficiency was noticeable, but so was the effect on complexity of the engine. In 1931 he returned to the RAE to take charge of engine research, but it was not until 1938, when he became head of the Engine Department, that work on developing an axial-flow engine actually started. Joined by Hayne Constant, they started work on Griffith's original design, working with steam turbine manufacturer Metropolitan-Vickers (Metrovick). 1931 is a common year starting on Thursday. ... 1938 was a common year starting on Saturday (link will take you to calendar). ... Metropolitan-Vickers, or Metrovick, was a British heavy industrial firm of the early-to-mid 20th century formerly known as British Westinghouse. ...

After a short period Whittle's work at Power Jets started to make major progress and Griffith was forced to re-evaluate his stance on using the jet directly for propulsion. A quick redesign in early 1940 resulted in the Metrovick F.2, which ran for the first time later that year. The F.2 was ready for flight tests in 1943 with a thrust of 2,150 lbf, and flew as replacement engines on a Gloster Meteor, the F.2/40 in November. The smaller engine resulted in a design that looked considerably more like the Me 262, and had improved performance. Nevertheless the engine was considered too complex, and not put into production. 1940 was a leap year starting on Monday (link will take you to calendar). ... The Metrovick F.2 was one of the earliest jet engines, and the first British design to be based on an axial compressor. ... The Gloster Meteor was the RAFs first jet fighter aircraft, introduced into service only weeks after the Messerschmitt Me 262 in August 1944. ... The Messerschmitt Me 262 Schwalbe (Swallow) was the first operational jet powered aircraft. ...

Griffith's original rejection of Whittle's concepts has long been commented on. It certainly set back development of the jet engine in England by several years. His motivations have long been the topic of curiosity, with many people suggesting that his endless quest for perfectionism was the main reason he didn't like Whittle's "ugly" little engine.