The Materials' Group

Most reactor components and structural members are made from metals and metal alloys due, in large part, to their strength and ability to resist brittle fracture by plastic deformation. However, brittle fracture can occur when structural material cannot undergo extensive, or even limited, plastic deformation due to the effects of radiation exposure or other environmental exposure conditions. Certain irradiation conditions lead to the development of a damage microstructure where plastic flow is limited to very small volumes or regions of material, as opposed to the general plastic flow in unexposed materials. This process is referred to as flow localization or plastic instability. This process results in a fracture mode that appears to be brittle since only small volumes of the material are able to deform through plastic flow. Even though there is extensive plastic flow in the small, confined regions, deformation essentially results in brittle fracture since very little energy is required to induce fracture. This study will address the conditions under which plastic flow localizes to cause embrittlement; it will assess (i.e., model) the deformation process so that relevant material constitutive equations can be used in finite element structural analysis; and it will characterize the damage microstructure associated with flow localization.