February 2003 Influence of Interfacial Roughness on Fiber Sliding in Oxide Composites with La-Monacite 307 Table 1. Representative Residual Stresses in Composites of Monazite-Coated Fibers in a Polycrystalline Al, O3 Matrix Residual stress(MPa Stress component AL,O,/YAG AL,,/ZrO2 Radial (coating/fiber) Radial(matrix/coating) Circumferential(coating) 300 290 Axial(fiber) 1160 240 Values in this table are intended only as rough guide for relative stresses. They were calculated using a lowing Young's moduli and thermal Al2 YAG(350GPa8.5×10-6°c- YAG/AI fiber LaPo YAG/Al2 O3 fiber ● 2um 2um LaPo Fiber YAG/AlO3 Fig. 2. SEM micrographs showing ions of indentation cracks with Al, O,/YAG eutectic fibers:(a)uncoated fiber in alumina matrix(indentation located below region shown);(b) fiber coated with LaPO (indentation located out of field of views, as indicated in(d)); (c)same fiber as in(b) but showing egion further along the debonded interface(arrows indicate magnitude of sliding displacement across debond crack); (d) schematic showing locations of(b)Fig. 2. SEM micrographs showing interactions of indentation cracks with Al2O3/YAG eutectic fibers: (a) uncoated fiber in alumina matrix (indentation located below region shown); (b) fiber coated with LaPO4 (indentation located out of field of views, as indicated in (d)); (c) same fiber as in (b) but showing region further along the debonded interface (arrows indicate magnitude of sliding displacement across debond crack); (d) schematic showing locations of (b) and (c). Table I. Representative† Residual Stresses in Composites of Monazite-Coated Fibers in a Polycrystalline Al2O3 Matrix Stress component Residual stress (MPa) Sapphire Mullite Al2O3/YAG Al2O3/ZrO2 Radial (coating/fiber) 15 720 130 240 Radial (matrix/coating) 25 630 140 240 Circumferential (coating) 300 420 290 280 Axial (fiber) 7 1160 240 420 † Values in this table are intended only as rough guide for relative stresses. They were calculated using a coaxial cylinder analysis,22 assuming a temperature change of T  1000°C, coating thickness of 2 m, zero volume fraction of fibers, and the following Young’s moduli and thermal expansion coefficients (nominal isotropic, temperature-independent values): polycrystalline Al2O3 (400 GPa, 8 106 °C1 ); sapphire (400 GPa, 8 106 °C1 ); mullite (200 GPa, 4 106 °C1 ); Al2O3/ZrO2 (300 GPa, 9 106 °C1 ); and Al2O3/YAG (350 GPa, 8.5 106 °C1 ).23–25 February 2003 Influence of Interfacial Roughness on Fiber Sliding in Oxide Composites with La-Monazite 307