13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- irradiation swelling occurs in nuclear fuels, and their thermal conductivity is degraded due to nuclear fissions; the metal materials within fuel elements experience irradiation damage effects, such as irradiation hardening and creep [13]. Besides, for the dispersion nuclear fuel plate, the research of nuclear reactor physics indicates that the irradiation damage along the length direction is heterogeneous owing to the non-homogeneous distribution of fast neutrons. All the above researches haven’t well taken the irradiation damage effects into account, and a good simulation method for un-uniform irradiation conditions is waiting to be developed. In order to study the thermo-mechanical behaviors of a whole fuel plate under non-homogeneous irradiation conditions, in this study, based on micromechanics, an equivalent fuel meat is obtained with the homogenized thermo-mechanical material properties related to the ones of fuel particles and metal matrix. With the thermo-elastic and irradiation swelling effects in the equivalent fuel meat, and with the thermo-elasto-plastic and irradiation hardening behaviors involved in the metal cladding, the respective three-dimensional thermo-mechanical constitutive relations and stress update methods are constructed. Assuming that the heat generation rates and neutron flux along the plate length direction are linear with the maximums appearing in the middle location, the numerical simulation methods are realized through several subroutines in ABAQUS. The material points have been given different constitutive relations according to time and their locations, thus the time and location-dependent constitutive relation can be carried out. The proposed numerical method is validated and the un-uniform thermo-mechanical fields are obtained and analyzed. 2. The constitutive relations and numerical simulation methods The whole fuel plate is regarded as the research object in this study and its thermo-mechanical behaviors evolution is focused on under the heterogeneous irradiation conditions. In the fuel meat, there contain a large number of fuel particles. It is impossible to consider the mutual interactions between the fuel particles and the matrix in the finite element model and it is necessary to deal with it as an equivalent homogenous material. As follows, the equivalent thermo-mechanical parameters are obtained on the base of homogenization theory. Owing to the temperature-dependent and time-dependent performances of the component materials together with the resultant location-dependent ones due to the heterogeneous irradiation conditions, the equivalent meat also has the above special properties. For the fuel cladding, the irradiation hardening effect is included in the large-deformation thermo-elasto-plastic behaviors. For the fuel meat and cladding, the thermal constitutive relations are comparably simple, which can be implemented with the subroutine UMATHT. According to the temperature, location and real time of the incremental step, the integration points can be applied with different thermal constitutive relations. In the following, the mechanical constitutive relations are mainly built and the relative numerical simulation methods are given. 2.1. Constitutive models of the equivalent fuel meat 2.1.1. Parameters of the equivalent meat Homogenization theory [14-15] has been introduced to a dispersion nuclear fuel meat, and the
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