Multiscale modeling of the mechanical properties of Nextel 720 composite fibers

The mechanical behavior of Nextel 720 ceramic matrix composite fibers was modeled using a novel multiscale modeling technique called the Bridging Cell Method (BCM). The BCM divides the system into three domains: atomistic, bridging, and continuum; with seamless coupling between the atomistic and continuum domains. The BCM allows considering the effects of the nano- and micro-structural characteristics of the material when modeling a macro-scale bulk. It incorporates interatomic potentials and quasi-harmonic calculations to find the final state of the system. The mechanical properties of the as-received fibers were investigated in tension via microtesile testing. The experimental results - evaluated in terms of the ultimate tensile strength, failure strain, and elasticity of the fibers under uniaxial loads - stood within the range reported in the literature; these results were then used to validate the Nextel BCM model. The Nextel BCM was conducted in two steps. First, the atomistic structure was relaxed. Then, a nano-crack was introduced in the mullite/alumina interface and the structure was pulled under a uniaxial tensile load until failure occurred. The BCM results indicated a good match between the Nextel BCM model and the experimental results. The validated Nextel BCM model can be used for the structural analysis of fibers.