For more than 350 years, since the time of Galileo, the design of mechanical structures has been based on the principle that the strength of materials is independent of the size of the specimen. But now, as mechanical structures are being created on a smaller and smaller scale, we are finding that this basic principle is beginning to break down. We are finding that “smaller is stronger.” Some of these effects can be attributed to the gradients of strain associated with deformation at a small scale, but, within the past half-decade, we are finding that the strength of metal crystals is size-dependent even in the absence of strain gradients. Here we show that these size effects begin to arise when the specimen size approaches the spacing between the defects that control plasticity. This has changed the paradigm for predicting the mechanical behavior of mechanical structures.
obtained his Ph.D. degree in Materials Science from Stanford University and immediately joined the faculty at Stanford. In 1989, he was named the Lee Otterson Professor of Engineering and served as Chairman of the Department of Materials Science and Engineering from 1991 to 1996. He became Professor Emeritus in 2003. He is a member of National Academy of Engineering, American Academy of Arts and Sciences, and National Academy of Sciences and a fellow of the American Society for Metals, the Metallurgical Society of AIME, and MRS. He received 3 honorary doctorates and numerous awards from ASM, TMS, ASME and MRS such as the Albert Sauveur Achievement Award from ASM, the Robert Franklin Mehl Award from TMS, the Acta Metallurgica Gold Medal, the Nadai Medal from the ASME, the von Hippel Award from the MRS. He is co-author of 450 publications and the book "The Principles of Engineering Materials".