For some 70 years the impact of Sir Alan Cottrell's work on the basic understanding of materials and its application to engineering structures, his academic leadership, his role of Scientific Adviser to the Government, and his contributions to safe nuclear energy, have been immense. He was the most influential physical metallurgist of the 20th century. Through his pioneering researches, and as an educator, he influenced countless students, scientists and engineers and will continue to do so. His papers and books are remarkable for their clarity.
Alan Howard Cottrell was born in Birmingham in 1919, attended Moseley Grammar School and then read metallurgy at Birmingham University, graduating in 1939. He was put on war work, introduced to a serious problem of cracking of armour plating of tanks at electric arc welds, which he solved.
He was made Lecturer in 1943, and in his course "Theoretical Structural Metallurgy" (the basis of a classic book), he discussed the structure and properties of metals in terms of the behaviour of atoms and electrons. This course helped transform a hitherto rather qualitative subject into a quantitative discipline, and was an important step in achieving his ambition to transform metallurgy into materials science. He was a brilliant lecturer, conveying complex phenomena in simple terms.
After the war Cottrell started research on the plastic properties of metals. In a series of penetrating and elegant studies he showed how certain crystal defects called dislocations (through their interactions with impurities) determine some important features in the ductile behaviour of structural steels, and how their mutual interactions control hardening of metals by cold working. In 1953 he published another influential book, Dislocations and Plastic Flow in Metals. He was given a personal Professorship in 1949 and in 1955 was elected to The Royal Society at 35.
In 1955 he became Deputy Head of the Metallurgy Division at Harwell. One of his pioneering researches there, on creep of uranium under neutron irradiation, led to a redesign of the fuel rods in Magnox civil nuclear reactors. His study on the hardening and embrittlement of steel by neutron irradiation has a direct bearing on the integrity of pressure vessels in nuclear reactors. In October 1957 a reactor at Windscale caught fire during a gentle heating to anneal damage in the graphite core, causing a national emergency. Cottrell set up a new laboratory in two weeks; he and his team were able to give an assurance that the Magnox reactors would be immune to this self-heating effect.
In 1958 he became Head of Metallurgy at Cambridge, transforming the department into a world-class institution, bringing in new people and equipment, teaching the subject from the atomic point of view and starting new research projects. His own researches focussed firstly on the brittle fracture of structural steel at freezing temperatures, responsible for many accidents on ships and bridges, and secondly, with Anthony Kelly, on the physics of fibrous composites. This led to new materials such as fibreglass and carbon fibre.
His work on fracture included the development of the theory of elastic-plastic cracks, the elucidation of the basic processes of failure at the tip of a sharp notch, and a theory of cleavage cracking in iron. These were important advances in understanding and in ensuring structural integrity.
In 1964 Cottrell became Sir Solly Zuckerman's deputy at the Ministry of Defence. Although reluctant to leave the university, he had become concerned with the need to invigorate British manufacturing through technology, and felt Whitehall was the place to do this. Working on Denis Healey's defence review, Cottrell led studies on the problems, in particular the cost, of a military presence in the Near and Far East. This led to the abandonment of the government's East of Suez policy.
In 1966 he followed Zuckerman to the Cabinet Office as Deputy Chief Scientific Adviser. He tackled various problems with scientific aspects, including the brain drain, environment and pollution, the Advanced Passenger Train and the Torrey Canyon oil spill.
In 1971 Cottrell became Chief Scientific Adviser, his position complicated by the arrival of Victor Rothschild and his Central Policy Review staff. Cottrell became involved in a proposal to make the work of the Research Councils more related to national needs while retaining their independence, which led to the controversial "Customer-Contractor" principle, under which government departments could commission research from the Research Councils. He was not comfortable with the machinations of Whitehall; he played it straight, and used his intellect to make his case, however unpopular.
In 1974 Cottrell expressed his concern to the Select Committee on Science and Technology about the integrity of the steel reactor pressure vessel, which is critical to the safety of the Pressurised Water Reactor, promoted by Walter Marshall, in the civil nuclear programme. Marshall set up a committee, and in the early 1980s, following the Marshall Report, Cottrell agreed that provided certain conditions were satisfied a sufficiently robust safety case could be established.
The Report, with Cottrell's endorsement, had a major impact on the Sizewell B inquiry and on getting Nuclear Installation Inspectorate approval, and led to major advances in the requirements for ensuring the integrity of pressure vessels and other large structures. Cottrell believed that nuclear energy was an important source of power, but also felt the public should be able to form a rational view, so he set out the facts in simple terms in How Safe is Nuclear Energy? (1981).
In 1974 Cottrell became Master of Jesus College, Cambridge, glad to return full-time to his family and academic life. He supervised a major revision of the College Statutes and prepared for the admission of women. He was Vice Chancellor for two years, from 1977, introducing the new Chancellor, Prince Philip, to the intricacies of the university's operation. He also prepared for the arrival of Prince Edward as an undergraduate. In 1986 he retired, returned to the Metallurgy Department, and researched the application of modern electron theory of metals to metallurgical problems, such as embrittlement of metals by certain impurities. In 1988 he published the excellent Introduction to the Modern Theory of Metals, followed by Chemical Bonding in Transition Metal Carbides.
From 1996 he cared full-time for his wife Jean, who suffered from Parkinson's disease; she died in 1999. During the last few years he published again on the plasticity of metals. Cottrell was a kind, gentle, sensitive and supportive person, modest, with a sense of humour and a brilliant intellect. Among his many awards and honorary degrees was the highest award of the Royal Society, the Copley Medal, in 1996; he was the first metallurgist to receive the Medal since it was instituted in 1731.
In the years 1965 to 1974, when he occupied positions giving advice to government, both on defence and then across the board in Whitehall, Alan Cottrell was a frequent and welcome speaker and contributor at the Parliamentary and Scientific Committee and willingly accepted our invitations to working/discussion dinners after his presentations, writes Tam Dalyell. When, as honorary secretary I thanked him for coming on one occasion, he replied half joking, and wholly in earnest, "it is one of my duties to educate you politicians in military and scientific issues."
And he did educate us. When I mentioned to Denis Healey, then his "boss", as Secretary of State for Defence, what Cottrell had said, he snorted, "You aren't the only ones he educates – Alan educates me too, and Fred Mulley" (then Healey's deputy at Defence). In 1977 Dr John Kendrew FRS, Nobel Prize-winner for chemistry in 1962, and part-time scientific adviser for the Ministry of Defence from 1960 to 1963, reflected to me, "I only wish I had as much influence on government as Alan Cottrell." Cottrell was indeed a powerful influence – for the good.
Alan Howard Cottrell, physical metallurgist: born Birmingham 17 July 1919; Kt 1971; married 1944 Jean Harber (died 1999; one son, one adopted daughter); died 15 February 2012.
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