Structural optimization, a broad interdisciplinary field, requires skillful combining of mathematical and mechanical knowledge with engineering. It is both intellectually attractive and technologically rewarding. The Symposium on Optimization in Structural Design was the second IUTAM Symposium in Poland. Fifteen years have elapsed since the Symposium on Nonhomogeneity in Elasticity and Plasticity, presided by Professor Olszak, was held in Warsaw. These fifteen years mean a lot for mechanics in Poland. Continuing the tradition of Professor Maksymilian Tytus Huber's research, considerable development of the mechanical sciences has been achieved in this country mostly due to the knowledge, vision and persistence of Professors Wit old Nowacki and Waclaw Olszak, eminent Members of our Academy. The Institute of Fundamental Technological Research was established, competent research groups grew, matured and contri buted to thermo-elasticity, plasticity, general theory of constitutive equations, and to structural mechanics-just to mention a few do mains. Mechanics is now penetrating into the technology of this country at an accelerating pace. The optimization in mechanics has a tradition in Poland. In 1936 Professor Zbigniew Wasiutynski formulated the optimality criterion for mean stiffness design using an elastic energy concept. Further work in this field has been done since, mostly in the last ten years. On behalf of the Committee for Mechanics of the Polish Academy of Sciences I wish to thank the IUTA1V Bureau for the decision to hold in Warsaw the Symposium the present volume contains the contribu tions to."

The theory of plasticity has a broad range of applications in industry and engineering. Its methods permit to devise metal processing, allow to assess safety of structures against collapse, make possible to estimate flow of bulk solids. The technological progress calls both for deeper understanding of sources of plastic deformation and for more rigorous description of mecha nisms of plastic motion. It was felt at the Institute of Fundamental Technological Research in Warsaw several years ago that an international meeting bringing together experts in various domains of plasticity and studying plastic behavior from different positions could be of use for further development of the discipline itself and for its service to society. The appropriate occasion for such a meeting sponsored by the Polish Academy of Sciences was provided by the 70th anniversary of Professor Wadaw Olszak. The idea of a fundamentals oriented symposium was favorably received by the scientific community over the world. Eminent scientists generously advised me as to the scope of the meeting and helped in shaping the program. It was eventually decided to concentrate the debates on a) physical foun dations of plasticity, b) thermodynamics of plastic and visco-plastic deform ation, c) experiments regarding plastic behavior, d) mathematical methods in plasticity, e) computer techniques suitable for solving important techno logical problems. The selection of papers was made accordingly. The symposium contributed papers were published in the volume entitled 'Foundations of plasticIty' and in the 'Archives of Mechanics' No.3, 1972."

Als GALILEI die naturliche Frage nach der Tragfahigkeit eines Krag balkens, der am freien Ende mit einem Gewicht belastet ist, in seinen "Discorsi e dimostrazioni matematiche" aus dem Jahre 1638 als erster quantitativ zu beantworten versucht, nimmt er an, dass sich der "Wider stand" des Materials gleichmassig uber die von ihm angenommene Zug zone verteilt und dass dieser Widerstand mit der Zugfestigkeit uber einstimmt. Offenbar erkannte der grosse Italiener intuitiv, dass in einem Balken alle Reserven des Tragwerks mobilisiert werden mussen, bevor es endgultig zerstoert werden kann. Fast zweihundert Jahre bewegte das Problem der Bruchfestigkeit der Tragwerke das Denken der Mathemati ker und Ingenieure, bis unabhangig voneinander YoUNG und mit absoluter Klarheit NAVIER den elastischen und den plastischen Vor formungsbereich eines Balkens voneinander trennen. NA VIER stellt fest, dass in demjenigen Bereich, in welchem die Verformungen proportional der Belastung sind, verhaltnismassig einfache mathematische Bezie hungen formuliert werden koennen, dass aber jenseits dieses Bereiches die entsprechenden Zusammenhange recht kompliziert werden. Ins besondere sei es sehr schwierig, mit mathematischen Mitteln die Trag fahigkeit eines Balkens beim Bruch anzugeben. Die Elastizitatstheorie beherrschte seitdem die Forschung und wurde auf eine hohe Entwicklungsstufe gebracht. Sie wird zur Zeit nicht nur auf die wenigen Materialien angewendet, bei denen die Dehnungen tatsachlich eine lineare Funktion der Spannungen sind, sondern meist auch auf viele andere technische Baustoffe, die einem solchen Verfor mungsgesetz nicht folgen.