National Academy of Engineering Memorial Tributes: National Academy of Engineering, Volume 10
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Memorial Tributes: National Academy of Engineering, Volume 10

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             GEORGE R.IRWIN                                           147
                             GEORGE R.IRWIN
                                  BY JAMES W.DALLY
                DR. GEORGE R.IRWIN, Glenn L.Martin Professor of Engineering at the
            University of Maryland and professor emeritus of Lehigh University, died of
            congestive heart failure at his home in College Park, Maryland, on October 9,
            1998. The Father of Fracture Mechanics, he was internationally known for his
            study of fracture and his ability to convert his scientific concepts into engineering
            methods applicable to a wide range of industrial applications involving a variety
            of structural materials.
                George was born on February 26, 1907, in El Paso, Texas, son of William
            Rankin Irwin and Mary Ross Irwin. His family moved to Springfield, Illinois,
            were he attended and graduated from high school. He attended Knox College in
            Galesburg, Illinois, and was awarded an A.B. degree in English in 1930. He
            studied physics for an additional year at Knox College before transferring to the
            University of Illinois at Urbana. From 1931 to 1935, he was a graduate student
            and part-time assistant in the Physics Department at the University of Illinois.
            During this period in 1933, he married Georgia Shearer, who was a classmate
            from Knox College.
                He returned to Knox College as acting assistant professor of physics,
            teaching there for only one year. The first of their children, Joseph Ross, was born
            in Galesburg, Illinois, during this year. Returning to the University of Illinois as a
            service fellow, he completed the requirements for a Ph.D. in 1937. His doctoral
            thesis was on the mass ratio of lithium isotopes.
             GEORGE R.IRWIN                                           148
                In July 1937, George joined the staff of the U.S. Naval Research Laboratory
            (NRL), Washington, D.C., to lead a small group of engineers and scientists
            specializing in ballistics with special emphasis on projectiles penetrating targets.
            By the time of U.S. involvement in World War II, he had developed a
            straightforward but exacting technique for measuring penetration force, and its
            time derivative as a projectile engages a target. He personally conducted a series
            of penetration experiments using his new method. It was the first time in the long
            history of ballistics that these fundamental measurements had been made.
            Although this research was carried on during the war, the important work was
            not published until 1946 as “Penetration Resistance at Ballistic Speeds” in the
            Proceedings of the Sixth Congress for AppliedMechanics. The new experimental
            method enabled the Ballistic Branch at NRL, under George’s direction, to
            develop several nonmetallic armors that were used for fragmentation protection in
            the Korean and Vietnam Wars.
                George’s interest in brittle fracture was initiated by his observation of armor
            plate, which chipped and cracked in a brittle manner during proof firings
            involving thick plates. He noted that this steel appeared to be ductile in standard
            Charpy impact fracture tests with small specimens. He deduced correctly that rate
            and size effects changed the mode of failure from ductile to brittle. He was most
            concerned with the gradient of the stress near a crack tip.
                In 1946 George was given the responsibility for the project on brittle
            fracture at NRL. He changed its direction and focused on the locally concentrated
            stress and deformation at the crack tip. The fertility and power of this new
            technical approach soon became apparent. George was promoted from head of
            the Ballistics Branch of the NRL to associate superintendent of the Mechanics
            Division in 1948. Two years later, he was promoted to superintendent and served
            in that capacity until his retirement from government service in 1967.
                The classical approach to brittle fracture in the late 1940s had been
            developed in the early 1920s, following the work of A.A.Griffith. Griffith had
            shown that an instability criterion could be derived for cracks in brittle materials
            based on the varia
             GEORGE R.IRWIN                                           149
             tion of potential energy of the structure as the crack grew. The Griffith approach
             was global and could not easily be extended to accommodate structures with
             finite geometries subjected to various types of loadings. The theory was
             considered to apply only to a limited class of extremely brittle materials, such as
             glasses or ceramics. George observed that the fracture process in metals involved
             nonelastic work at the crack tip. This observation permitted him to modify the
             Griffith theory by incorporating a plastic work of fracture in addition to the
             classical surface energy of crack formation.
                Confusion was widespread in the literature of that era because it was not
             clear how a Griffith-style global energy balance related to the local physics of
             separation processes at the crack tip. George showed definitely in his 1950 papers
             that the global flux of energy to the fracture process, appearing in that overall
             balance, was fully explainable in terms of the locally concentrated fields of stress
             and deformation at the crack tip. Even more important, he showed, in the
             common case when the zone of nonelastic deformation occupied only a small
             region surrounding the crack tip, that the mathematical equations of elasticity
             have singular solutions for the stress fields near the tips of the cracks. These
             solutions were of a universal form involving a multiplying factor, now termed a
             “stress intensity factor” proportional to the loading. This stress intensity factor
             depended on the geometry of the structure and the applied loading. With these
             pioneering papers of the early 1950s, George had given birth to fracture
                After introducing the fundamental concept of the “stress intensity factor,”
            which clarified the issue of fracture for the mechanics community, George moved
            into the materials area. He noted that the stress intensity factor could be employed
            as a crack tip characterizing parameter. He proposed that the conditions for the
            onset of crack growth could be phrased in terms of attainment of critical stress
            intensity factor KIc, a material property. The concept of a critical stress intensity
            factor is now universally accepted as a proper measure of resistance to crack
            growth, and rates of subcritical crack growth by fatigue and chemical attack are
            represented as functions of the stress inten
             GEORGE R.IRWIN                                           150
             sity factor. Much of current activity developing nonlinear theory for ductile
             metals and polymers proceeds in a similar spirit by identifying appropriate
             characterizing parameters from the near crack tip singular solutions to the
             nonlinear continuum mechanics equations.
                George recognized the huge gap between publication and practice and
             invested years of persistent effort needed to introduce new fracture mechanics
             methods to applications in industry. This was a major effort because some of the
             areas of structural technology had techniques that were not readily replaced. He
             also provided leadership and significant effort to many of the committees of the
             American Society for Testing and Materials (ASTM). Many of the standards
             developed by the ASTM committees for testing materials to establish fracture
             parameters are due in large part to George’s work over more than two decades.
                In 1967, after thirty years of service, George retired from his position as
            superintendent of the Mechanics Division at NRL and joined Lehigh University
            as the Boeing University Professor. He served on the faculty at Lehigh University
            for five years before reaching mandatory retirement age. During this initial period
            in the academic community, he interacted with many researchers and influenced
            their work. For example, during his tenure at Lehigh University, he influenced the
            work of Paul Paris in developing methods for predicting crack growth and its
            control in aircraft structures and of F.Erdogan on cracks in thin-walled shell
            structures. The list of others who either collaborated with George or were
            influenced by him is long. Only a few notable researchers are listed here:
            A.A.Wells of the British Welding Institute on characterizing fracture in normally
            ductile steel structures; F.A.McClintock, Massachusetts Institute of Technology,
            and J.W.Hutchinson, Harvard University, on the development of fracture
            mechanics procedures in the presence of substantial ductility; Jim Rice, Harvard
            University, on developing the J integral approach for characterizing the onset of
            crack growth in ductile materials; L.B.Freund, Brown University, and
            M.F.Kanninen, Southwest Research Institute, on the dynamics of inertial limited
            crack propagation and arrest.
              GEORGE R.IRWIN                                                             151
                   After retiring for the second time from Lehigh University in 1972, George
              joined the faculty at the University of Maryland in College Park. I was then
              serving as chair of the Mechanical Engineering Department when George decided
              to join us. We were elated, and he formed the center of a small group, with an
              experimental focus, working in the area of dynamic fracture. At that time we
              were concerned with crack arrest and its implications in a loss-of-coolant
              accident of a nuclear reactor. With his guidance we were able to establish a
              measure of crack arrest toughness and to develop a test standard for its
              measurement in tough reactor-grade steels.
                   The list of honors bestowed on George is long, but they all are worthy of
              1946    Naval Distinguished Civilian Service Award
              1947    Knox College Alumni Achievement Award
              1959    ASTM Charles B.Dudley Medal
              1960    RESA Award for Applied Research
              1961    Ford Foundation Visiting Professorship, University of Illinois
              1966    ASTM Award of Merit
              1966    American Society of Mechanical Engineers (ASME) Thurston Lecture
              1967    Fellow, ASTM
              1969    University of Illinois Engineering Achievement Award
              1969    U.S. Navy Conrad Award
              1969    Alumni Achievement Award, University of Illinois
              1973    SESA Murray Lectureship Award
              1974    Lehigh University Academic Leadership Award
              1974    ASTM honorary member
              1974    American Society for Metals Sauveur Award
              1976    The Grande Medaille Award of the French Metallurgical Society of France
              1977    ASME Nadai Award
              1977    B.J.Lazan Award from the Society for Experimental Mechanics
              1977    Honorary degree, doctor of engineering, Lehigh University
              GEORGE R.IRWIN                                                             152
              1977    Election to the National Academy of Engineering
              1978    ASTM-Irwin Award
              1979    Francis J.Clamer Clauier Medal of the Franklin Institute
              1982    Governor’s Citation for Distinguished Service to Maryland
              1982    Tetmajer Award of the Technical University of Vienna, Austria
              1985    Fellow, Society for Experimental Mechanics
              1986    ASME Timoshenko Medal
              1987    ASM Gold Medal for Outstanding Contributions to Engineering and Science
              1987    Elected to foreign membership, British Royal Society
              1988    ASTM Fracture Mechanics Award and the George R. Irwin Medal
              1989    Honorary membership in Deutscher Verband für Material Prufung
              1990    Honorary membership in the American Ceramic Society
              1990    Albert Sauveur Lecture Award
              1992    George R.Irwin Research Award, University of Maryland
              1993    Engineering Innovation Hall of Fame at the University of Maryland
              1998    A.James Clark Outstanding Commitment Award University of Maryland
              1998    Appointed Glenn L.Martin Institute Professor of Engineering
                   George is survived by his wife, Georgia Shearer Irwin, of College Park,
              Maryland; four children, Mary Susan Gillett of Dunkirk, Maryland, Sarah
              Lofgren of Berwyn Heights, Maryland, Joseph R.Irwin of Seabrook, Maryland,
              and John S.Irwin of Raleigh, North Carolina; ten grandchildren and four great-
                   George will long be remembered by all of us in the engineering profession
              as a remarkable engineer and scientist. But I will remember George more as a
              gentle man than an outstanding
             GEORGE R.IRWIN                                           153
             engineer. He had so much character it is impossible to describe. He was never
             assuming or presumptuous. Many men of achievement become filled with
             themselves. Not George R.Irwin—he remained humble in spite of his long list of
            awards and accolades. He sought no glory or legacy. He shared his ideas and was
            pleased to see others develop his initial concepts. Our research group often
            gathered in his office to discuss our ongoing work in the dynamics of fracture—I
             will always remember his quiet ability to keep us on track and to guide us through
             difficulties. We will sorely miss him.
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