** Specimen Size Effects on Mechanical Tests for Candidate Structural Materials Targeted for Fusion Reactors** Fusion is considered as an ideal energy solution in future. However, high energy neutron flux can degrade structural materials in fusion reactors through irradiation damage. The unrelenting service condition necessitates reliability tests on the mechanical properties of materials that have been exposed to irradiation. Restricted by the limited irradiation volume in fusion neutron irradiation facilities under construction, small size specimens have to be used for mechanical test after irradiation. The key challenge of using specimens with reduced dimensions is that the test results are strongly dependent on specimen size and shape. Therefore, the project is to study specimen size effects on mechanical tests for candidate structural materials targeted for fusion reactors.
Earlier experimental studies have reveal some phenomenological mechanisms for specimen size effects. However, it is necessary to take into account the influence of microstructure and irradiation for more physical-based models. Applying multi-scale modeling including dislocation dynamics, crystal plasticity theory and continuum mechanics, we can not only obtain specimen size effects for materials before irradiation, but also predict specimen size effects after fusion neutron irradiation. Before irradiation, specimen size effects can be studied via both experiment and simulation. We plan to prepare and test series of specimens with different sizes for different mechanical tests, such as uniaxial tensile, creep, fracture toughness and fatigue, and to character microstructure in these specimens. Meanwhile, corresponding multi-scale model will be built and revised by macroscopic mechanical properties and microstructure. On the other hand, simulation is a more reasonable way to analyze and predict size effects after irradiation, especially for fusion neutron irradiation, due to the limited volume in irradiation facility. This method can help us understand the essential of size effects in depth, and guide specimen design and assembly in engineering.
Professor Yao Shen focuses on the relationship between microstructure and mechanical properties in materials, especially the meso- and micro-scale experimental characterization of deformation process, such as digital image correlation (DIC), measurement of grain-scale plastic deformation and TEM characterization of grain boundary and dislocation behavior, and simulation from macro- to micro-scale of these behaviors with modeling, including continuum FEM with damage model, crystal plasticity FEM dislocation dynamics, molecular dynamics and phase field models. Professor Lei Zhang’s research interests are in the design of multi-scale methods and numerical analysis, including the numerical homogenization method of multi-scale inhomogeneous media, and the design and analysis of atomic/continuum coupling methods. He first designed a compatible energy coupling method in the two-dimensional general atoms/continuum interface, and gave the error estimates and the rigorous mathematical proof.