UCLA

High-temperature composite materials have broad applications in the energy and transportation sectors because of their unique capabilities to sustain strength at elevated temperatures, inert interaction with some coolants, and their high strength-to-weight ratio. These encompass C/C and SiC/SiC composites, developed as cladding in fission reactors, and as turbine blade materials for advanced jet engines and combustion liners. Cyclic thermal and mechanical loading associated with neutron irradiation effects of these composites leads to wide-spread and progressive micro-cracking that leads to loss of thermal conductivity and further enhancement of thermo-mechanical damage. A physics-based model of wide-spread micro-crcaking is developed within the thermodynamic framework of continuum damage mechanics. Evolution equations for damage parameters that describe the growth of continuum damage are developed, where the material variables are obtained from experiments. The model novelty is in coupling mechanical, thermal, and irradiation damage through a consistent thermodynamic framework, including loss of thermal conductivity due to the evolution of mechanically induced micro-cracks. A number of thermo-mechanical experiments were conducted to confirm model assumptions. The model is shown to be validated with out-of-pile experiments, and then implemented using commercial finite element code COMSOL to the fuel cladding problem and FNSF blanket where coupling between different physics was achieved along with an implementation of global local approach. Finally, a set of performance diagrams for a thin-walled SiC tube structure subjected to cyclic thermo-mechanical loading associated with neutron irradiation were introduced to aid the community with first stage design tool for a thin walled CMC cylindrical structures.