Exploiting New Opportunities in Materials Research by Remembering and Applying Old Lessons

Recalling some of the progress that has been made in understanding the mechanical properties of materials over the past 50 years or so reveals the importance of remembering and applying old lessons when addressing new opportunities in materials research. Often, the classical lessons of the past are especially useful as a guide for thinking about new problems. Such an approach to new problems is intimately connected to the creation of simple models that capture the essential features of the phenomena involved. Experience shows that, although such efforts might not pay off immediately, they come to be useful many years later when new problems are confronted. The merit of applying old lessons to new problems is described herein by using examples from the author's career in characterizing and understanding the mechanical properties of materials. It is hoped that these lessons are sufficiently general to be applied to other areas of materials research. Problems ranging from the high-temperature creep resistance of titanium aluminides, to the residual stresses in deposited thin films, to diffusive relaxation processes in thin films, to the size dependence of the strength of crystalline materials at the nanometer scale, all provide examples of how applying lessons of the past can help to understand new problems. An effort is also made to identify new, emerging problems in materials research where the application of the lessons of the past, together with new capabilities of the future, can come together to produce a fresh understanding of material behavior.