Pieter Cornelis Tobias de Boer, a professor in the Sibley School of Mechanical and Aerospace Engineering for more than 40 years, died May 2 at Kendal of Ithaca. He was 85.

De Boer’s academic interests included the thermodynamic analysis and optimal design of pulse-tube cryocoolers, which emerged in the 1980s and are used in semiconductor fabrication and other industrial and military applications.

Another area of recent interest was the rupture energy of pendular rings, with application to the attachment strength of thin films in microelectromechanical systems (MEMS) devices.

Born May 21, 1930, in Leiden, The Netherlands, de Boer earned both his undergraduate and master’s degrees in mechanical engineering in 1954 from Delft (Netherlands) University of Technology, and his doctorate in 1962 from the University of Maryland.

Between earning his master’s and doctorate, he served for two years in the Dutch military, rising to the rank of lieutenant. He married Joan Lieshout in 1956, and shortly thereafter the couple moved to Maryland, where their three children – Maarten, Claire and Yvette – were born.

After serving as assistant professor at Maryland from 1962 to 1964, de Boer and his family moved to Ithaca when he was hired by Cornell as assistant professor in the Graduate School of Aeronautical Engineering. He was promoted to associate professor in 1968, and to full professor in 1974, two years after the formation of the Sibley School of Mechanical and Aerospace Engineering.

De Boer retired in 2000 and was an emeritus professor in the Sibley School following his retirement.

At Cornell, de Boer taught courses in thermodynamics, fluid mechanics, combustion and mathematics, and conducted research in the areas of shock wave physics, engine emissions control, fuel injection, hydrogen fuels, Stirling engines and pulse tube generators.

“He was a good friend and colleague, and his research was way ahead of its time,” said Al George, the John F. Carr Professor of Mechanical Engineering.

In addition to his role as professor, de Boer served as associate director of the Sibley School from 1982 to 1991. He was the school’s “official or unofficial parliamentarian,” said colleague and emeritus professor John F. Booker.

“He knew Robert’s Rules of Order inside and out, and we always turned to him for that,” Booker said. “Tob was totally honest, totally without guile. He was a really good guy.”

During his tenure at Cornell, de Boer took summer and sabbatical leaves during which he conducted research at the Aerospace Corp., the von Karman Institute for Fluid Dynamics, Ford Motor Co., General Electric, Delft University of Technology, Centre National de la Recherche Scientifique in Paris, the Jet Propulsion Laboratory and the National Institute of Standards and Technology.

Away from academia, De Boer was an avid cyclist, distance runner, Nordic skier and triathlete, and participated in orienteering. He was president of the Finger Lakes Cycling Club, of which Stuart Leigh Phoenix, professor in the Sibley School, is also a member.

“He got me into cycling,” Phoenix said. “We went every day for quite a while, went around the lake many times. He was a fierce competitor, and probably instilled a lot of that in me, in cycling, and it carries over to other things, too.”

Perhaps de Boer’s most notable athletic achievement: He set a national age-group record by cycling 448 miles in 24 hours at age 48.

He was also founding president of the Cayuga Nordic Ski Club and treasurer of the Cascadilla Rowing Club.

De Boer is survived by his wife, children and five grandchildren. Donations in de Boer’s memory can be made to Cornell Engineering’s Department of Mechanical and Aerospace Engineering, or to Hospice of Ithaca. A memorial service will be announced at a later date.