In 1941, the Mechanical-Aeronautical branch was opened within the body of the Engineering School (former Istanbul Technical University) in Istanbul. This branch gave its first graduates in 1943 with only six people. The first among them, in order of diploma, is Ahmed Cemal Eringen, who was born on February 15, 1921, in Kayseri-Bünyan. 

Accepted as an authority in the field of continuum mechanics in the world, Eringen is unfortunately not known in his homeland, where he left at the beginning of his 20s. As the first aeronautical engineer educated in Turkey, who spent almost 60 years of his life in the USA, Eringen earned numerous achievements in his career, and his name is kept alive with a medal (Eringen Medal) in the USA every year. So, who is Ahmed Cemal Eringen, who came out of Kayseri and ended his career as a professor at Princeton University?1

We do not have detailed information about his period in Turkey. After his graduation in 1943, Cemal Eringen was sent to Glenn L. Martin firm in the USA for an internship to gain aviation experience like other graduates. After the practical training he received here, he worked at the Turkish Aeronautical Association (THK) Aircraft Factory in Ankara until 1947 (Images 1 and 2). Wanting to continue his studies in the academic field, he went to the USA again. He began his studies in rigid body dynamics under Prof. Nicholas (Miklós) John Hoff at Brooklyn Polytechnic Institute. Nicholas Hoff is a former assistant to renowned mechanics professor Stephen Timoshenko at Stanford. Eringen's Ph.D. was a project funded by the Office of Naval Research of the US Navy (Project No: N6onr-263-Task Order II).2 He received his doctorate in June 1948 with his thesis on the elasticity problem and buckling of sandwich beams (original thesis title: Solution of two dimensional - mixed boundary layer problem of elasticity for rectangular orthotropic media and application to the buckling of sandwich beams).3

Eringen transferred to the Illinois Institute of Technology (IIT) after his doctorate. He was assigned to lecture on engineering mechanics. The first thing he did was to establish a comprehensive library in this field at the faculty. He published his first academic article in June 1951. In this study, he examines the buckling of sandwich cylinders under load (original title: Buckling of Sandwich Cylinder Under Uniform Axial Compressive Load, Image 3).4 In the December 1951 issue of the Journal of Applied Mechanics, in which the article was published, Prof. George Gerard from New York University wrote a one-page commentary on Eringen's study.5 During his five-year term at IIT, Eringen established a research program in the field of elastodynamics. He also touches on topics such as the vibration of circular membranes and plate buckling.

When he transferred to Purdue University in 1953, he broadened his research interests from structural dynamics to continuum mechanics. In 1962 he published his first book of 477 pages titled Nonlinear Theory of Continuous Media. But Eringen has a more serious vision in mind. He wanted to bring a new perspective by combining natural sciences and engineering under one roof. He proposed ideas about using mathematics, physics, chemistry, and biology to solve engineering problems. The research team he created within this framework is a first in the USA. 

The concept of "engineering science" began to be cited in academia with the initiatives of Eringen. This definition means different things to many, has been interpreted contradictorily, and was initially discredited in academia. However, Eringen did not hesitate to take the necessary steps to realize this vision. In this context, he launched the International Journal of Engineering Science in 1963. In his writings and speeches, he states that engineering science plays an essential role in the development of people in technology-oriented societies. In the preface to the journal's first issue, he wrote that an engineer who lacks basic sciences would not be at a level to solve interdisciplinary technical problems. This newly established journal will be a new communication tool where natural scientists and engineers can meet on common ground.

On November 4, 1963, a few months after the establishment of the journal, Eringen gave the opening speech as the founding president of the Society of Engineering Science (SES) at an event with the participation of approximately 400 people from different branches (Image 4). He explains the purpose of the society as "the advancement of interdisciplinary research and the building of bridges between engineering and natural sciences." In a short time, the society collaborated with well-established associations such as the American Society of Mechanical Engineers and the American Society of Civil Engineers. Eringen was the president until 1973.

Eringen also applied his vision to his own academic work. He focused on interdisciplinary branches, not just one area. While at IIT, he mainly focused on classical elasticity and structural mechanics, while at Purdue, he studied wave motion and loads on structures such as beams, plates, and spheres. His research on random vibration and stochastic loads is one of the methods actively used in analyzing building structures against wind and earthquakes. In the 1960s, he also studies topics such as fluid dynamics, viscoelasticity, and electromagnetic interactions in solids and fluids.

Eringen, who transferred to Princeton University in 1966 after thirteen years at Purdue, became interested in turbulence, liquid crystals, polymers, composite materials, and biomechanics. The presence of world-renowned theoretical physicists at Princeton leads Eringen to physics-based branches. The postgraduate students, postdoctoral researchers, and visiting professors in his team continued to use Eringen's methods to study basic and applied sciences as a whole in the countries they went to. As the head of the Princeton University School of Civil Engineering Continuum Physics working group, Eringen spread his name all over the world with his publications on beam problems, surface physics, composite materials, electrodynamics, and superconductivity (Image 5). 

Founded by Eringen, the SES society has started to issue the Eringen Medal to an academician selected from among the candidates who have achieved success in engineering science since 1976. The first scientist to receive the Eringen Medal, the inventor of the concept of fuzzy logic, was the Azerbaijani mathematician Lotfi Zadeh (Lotfali Askar-Zadeh). In 1980, experts such as the Hungarian-born physicist Edward Teller, the inventor of the hydrogen bomb, and in 1993, Turkish-born Fazıl Erdoğan were deemed worthy of this award. Today, as a tradition that is still up to date, the Eringen Medal continues to be awarded to successful scientists7 (Image 6).

Until his retirement in 1991, Eringen published 13 books, 228 articles, 10 book chapters, 58 technical reports, and 13 non-technical articles throughout his career. He moved to Colorado during his retirement and continued his work there. The last article he prepared before his death was published as the preface to his book Mechanics of Generalized Continua: One Hundred Years after the Cosserats, published in 2010. He has joint articles with scholars from Turkey such as Erdoğan Şuhubi, Hilmi Demiray and Burhanettin Şemsi Altan. There is also a poetry book called "Pink Lily," published in Erzurum in 1937.

One of Eringen's doctoral students, Prof. James D. Lee, emeritus from George Washington University, gave the following information about Eringen: 8

Certainly, Professor Eringen was one of the few pioneers of Continuum

Mechanics. Besides, in his book [1], Professor Eringen included a chapter

"Electrodynamics of Continua" which was the birth of Continuum Physics.

Later, Professor Eringen and Professor Maugin [2, 3] presented the thermomechanical-electromagnetic coupling theory from a unified viewpoint.

This is the complete theory of continuum physics.

Since 1964, Professor Eringen had developed the microcontinuum field theories [4, 5] in which the medium is considered as an infinite collection of finite size and deformable particles. This is a giant step forward from classical continuum physics to micromorphic (including microstretch and micropolar) continuum physics. The formulation is systematic, comprehensive, and rigorous.

Meanwhile, Professor Eringen published a book "Nonlocal Continuum Field Theories" [2] which systematically presents field theories of electromagnetic solids and fluids with nonlocal effects in both space and time.

In summary, Professor Eringen's work enables us to study and perform research in the arena of nonlocal micromorphic continuum physics.

On Eringen's personality, first of all, Professor Eringen was a kind person. He treated students nicely and with respect. In doing research, Professor Eringen provided us (I was one of his Ph.D. students) with freedom and comprehensive (sometimes detailed) guidance.''

Continuum mechanics expert Prof. Gérard A. Maugin describes Eringen as: 9

''Eringen's renown as an educator, lecturer, and prolific author has attracted graduate students and visiting scholars from around the world. His style was markedly full of enthusiasm and not without this slight touch of charming naïveté that suits well great scientists. He was sought after throughout the world as a lecturer and had many presentations – at national and international congresses, symposia and summer schools – as well as so many lectures at academic institutions to his credit.

He did not like to engage in public controversies. He was extremely kind to all his students, co-workers, and visitors. The engineering science community at large has lost a great scientist, a friend, and a gentleman. Nobody served this community so dutifully and so-well for almost 60 years, as A. Cemal Eringen did through his seminal creative works and his untiring efforts of organization and dissemination of knowledge.''

Dr. Volkan İşbuğa, from Izmir Institute of Technology, describes the incident he witnessed while he was a doctoral student in Colorado as follows: 10

'' Eringen continued his work as a visiting professor at the University of Colorado. He gave a seminar in our department with the invitation of my doctoral thesis advisor, but I could not attend that seminar. My doctoral thesis was about a theory he developed. My teacher said he wanted to introduce us, but I was not lucky. After his death, I went to his house and met his daughter. Upon Eringen's will, Ms. Meva wanted to donate his entire library to the university he graduated from in Turkey or to another Turkish university. I contacted some universities, but there was no response. He had a truly enormous library. The University of Colorado also only accepted individual pieces since the books were available there. So I took pictures of some of Eringen's notes from his undergraduate days. I still have them. The International Journal of Engineering Science, of which Cemal Eringen is the editor-in-chief, published a special issue for Eringen after his death. Scientists working in the same field in the academic world were included in this issue, to which we also contributed.''

Prof. Erkan Öterkuş from the University of Strathclyde interprets Eringen's scientific studies as: 11

''Cemal Eringen is one of the leading figures in continuum mechanics. The most popular study topic now is 'nonlocal elasticity.' At the time of Cemal Eringen and those who worked with him on this subject, nanotechnology was not very advanced. As nanotechnology develops, both the subject of 'nonlocal elasticity' and the name Eringen have come to the fore more recently. Not only in Turkey but all over the world, Cemal Eringen is recognized and appreciated today, perhaps more after his death.

Eringen has worked on many different subjects. Among them, micromorphic formulation may become a much more popular topic in the near future with the development of new generation metamaterials. He also has pioneering studies on what we call 'multiphysics' analysis, that is, more than one physical event affects each other. 

They worked together with Ahmet Çakmak, the grandson of Marshal Fevzi Çakmak, at the Faculty of Civil Engineering at Princeton University. On the subject of rigid body dynamics, one should mention Fazıl Erdoğan and Ali Argon, along with Cemal Eringen. These professors are world-renowned scientists who are considered authorities in their fields.''

Prof. Cengiz Çamcı from the University of Pennsylvania summarized Eringen's fields of study as:12 

'' Mr. Cemal put forward an idea called 'unified field theory' in the field of continuum mechanics. He would put subjects such as fluid mechanics, rheology, heat transfer, elasticity, strength, thermodynamics, and liquid crystals into a single analytical framework. He did not deal with solution methods much, but he presented a magnificent analytical structure that looked at many issues from the same window. What Cemal Eringen offers is a comprehensive engineering science approach. These findings may not directly serve today's engineering solutions, but they are scientifically valuable in the very long run. Turkish scholars such as Atilla Aşkar, Akın Tezel, Fazıl Erdoğan, Nihat Berker and Esin İnan were influenced by Cemal Eringen.''

To sum up, Ahmed Cemal Eringen from Kayseri is the first Turkish aeronautical engineer who was born, raised, and educated in Turkey. He practiced his profession in his country for about three years. From 1947 when he moved to the USA, he continued his academic studies in this country until his death in 2009. The world-renowned Eringen school was not born in Turkey but in the USA. Although Eringen does not have a known specific contribution to aeronautical engineering, it is evident that he has made seminal contributions to many engineering branches with his scientific studies. It is a shame for all of us that such a valuable Turkish scientist is not recognized in his own country.