Warner Koiter

After completing his studies in mechanical engineering at Delft TU in 1936, Koiter worked at the Dutch National Aeronautical Research Institute in Amsterdam (today: National Aerospace Laboratory, NLR). It was here that he carried out air-worthiness tests on aircraft structures and structural analyses of two-spar wings with a shear-resistant skin. Following a brief period spent at the patents office in 1938, Koiter moved to the Government Civil Aviation Office in 1939, where he quickly became director of the engineering division. During World War 2, he carried out research work at the NLR and gained his doctorate in 1945 at the faculty of mechanical engineering at Delft TU with his ground-breaking dissertation entitled Over de Stabiliteit van het Elastisch Evenwicht [Koiter, 1945]. He completed this dissertation while his country was still occupied by the German armed forces. “Professor Flügge had been sent from Germany to Delft to cover the Rector chair. According to the occupant law, Ph.D. students who were willing to discuss their thesis were obliged to take an oath of allegiance to the Nazi government. Koiter’s thesis on the stability of elastic equilibrium was ready at that time, but the author, refusing this imposition, waited for the liberation of his country. The thesis thus appeared only in 1945” [Pignataro, 1998, pp. 605/606]. Four years later, Koiter was appointed to the chair of applied mechanics at Delft TU. NASA published his dissertation in English in 1960 (On the stability of elastic equilibrium). The chair of theory of strength and stability of structures created specially for Koiter at his Alma Mater in 1973 remained his workplace until his transfer to emeritus status in 1979. His research into the stability of imperfect elastic structures in the supercritical range was a great help in overcoming the dominance of linear thinking during the innovation phase of structural mechanics (1950–75). Koiter’s 150 or so research reports were acknowledged by the universities of Glasgow, Bochum, Ghent and Liège with honorary doctorates, the ASCE’s Von Kármán Medal and the ASME’s Timoshenko Medal. And as a further honour, the ASME inaugurated the Warner T. Koiter Medal in 1996, which was awarded to its namesake in the same year. The citation reads:"...for his fundamental work in stability of structures, for his diligence in the effective application of these theories, his international leadership in mechanics, and his effectiveness as a teacher and a researcher” (cited in [Pignataro, 1998, p. 605]). When Koiter died on 2 September 1997, the scientific world of structural mechanics lost not only one of its leading figures, but also an extraordinary personality:"Much less known has been, and perhaps still is to many people, the unparalleled human figure which was hidden behind the scientific one. His impeccable moral integrity was incompatible with any deviating compromise. ‘Samurai in a world of Pharisees’, but at the same time he was cordial, generous and deprived of arrogance” [Pignataro, 1998, p. 605]. The science director at the Koiter Institute at Delft TU, Prof. René de Borst, has provided us with a wonderful memorial to this magnificent researcher and teacher of structural mechanics in the shape of a biographyWarner Tjardus Koiter. Het instabiele hanteerbaar [de Borst, 2002].

Main contributions to structural analysis:

Over de Stabiliteit van het Elastisch Evenwicht [1945]; Stress-strain relations, uniqueness and variational theorems for elastic-plastic materials with a singular yield surface [1953]; General theorems for elastic-plastic solids [1960/1]; A consistent first approximation in the general theory of thin elastic shells [1960/2]; On the nonlinear theory of thin elastic shells [1966]; On the foundations of the linear theory of thin elastic shells [1970]; Stijfheid en Sterkte 1: Grondslagen [1972] 

Source: Kurrer, Karl-Eugen The History of the Theory of Structures, Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH, Berlin (Deutschland), ISBN 3-433-01838-3, 2008; p. 741/742