The fundamental concepts of physics are crucial to understand the correlation of the structure and strength of materials. Some materials, like a steel coil spring or rubber, are elastic. Grasping a rubber ball deforms the shape momentarily before it returns to its original state. Other materials when manipulated with, such as clay, will retain its newly deformed shape.
This phenomenon, called plasticity, has been studied by scientists in designing high strength steels and alloys. The demand for high-technology metallic materials continues to depend on further research and understanding of plasticity in order to strengthen and optimize the performance of metals.
Now material scientists at POSTECH’s Graduate Institute of Ferrous Technology (GIFT) have developed a new theory for plasticity for structural materials. The research, carried out by doctoral student Minho Jo and Professors Yang Mo Koo and Se Kyun Kwon, in collaboration with Professor Byeong-Joo Lee at Department of Materials Science and Engineering of POSTECH and Professors Börje Johansson and Levente Vitos of the Royal Institute of Technology (KTH) in Sweden, is being published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
To date, no reliable microscopic theory of plasticity has been presented. For this paper, the researchers demonstrate a unified solution to plasticity by using molecular dynamics simulations to address the grain orientation effect on the deformation modes of face-centered cubic metals. They derived a single parameter in the theory and proved that the parameter sufficiently identifies the activation of various plastic deformation modes. This finding leads to the simple deformation mode diagram as shown in the figure, which fully specifies the potential diversity of metals.
This deformation theory will have real-world application in the further study of what types of materials can be made to be stronger. As an example, the proposed theory will assist in the development of high-performance and energy-efficient automobile sheet by designing lighter but stronger metals and eliminating materials that weaken a structure.
Professor Kwon plans to do more research on plasticity with his team at GIFT. “Future studies will include extending to other structures such as body-centered cubic and hexagonal closed-packed,” said Professor Kwon. He is also interested in analyzing the plasticity of nanoscale materials.