Three mathematical models for use in calculating the stresses and displacements in two-, three- , and four-layer pyrolytic carbon and silicon carbide coatings on microspheres of (Th,U)C2 or (Th,U)O2 during reactor service have been previously described. In these models it is assumed that pyrolytic carbon changes dimensions anisotropically and will creep under fast-neutron irradiation, silicon carbide is dimensionally stable and undergoes no creep, and an internal pressure is generated due to gaseous fission products. Comparison of the results predicted by these mathematical models with irradiation tests shows agreement with diametral changes of two-layer fuel particles. Coating failure, presumably due to stress, occurred only in those samples with high calculated stresses.