Particulate inclusions in brittle composites: An assessment of the effects of temperature dependent phase changes
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abstract
External oxidation barrier coatings are routinely used to protect carbon-carbon composites against oxidation. These coatings, however, do not offer complete protection for the structure. In order to increase the effectiveness of the oxidation protection system, internal particulate oxidation inhibitors are being investigated as secondary protection against oxidation. These inhibitor particles react with oxygen to form an internal glassy sealant and impede further oxidation. These protection techniques, however, greatly complicate the analysis necessary to assess the performance of protected C-C structures. The change in laminate constitutive behavior is dependent on temperature, chemical reaction rates, the presence and distribution of inhibitors, internal defects, porosity, and time. As a preliminary demonstration of the phase change of the inhibitor particle as it oxidizes, a simplified finite element model was created. This model addresses the temperature dependent response of a rigid inclusion embedded in an orthotropic media. The material properties of the inclusion are temperature dependent to simulate glass formation. Preliminary results illustrate the sensitivity of the internal stress field to the type of material properties used for the inhibitor particle. Also, the location and distribution of pores within the material has an impact on the stresses incurred.
