Residual Stresses in Unidirectional Al2O3 Fiber/Silicate Glass Composites by X-ray Diffraction

Abstract

AbstractUnidirectional continuous fiber composites fabricated from 20 μm diameter α-AI2O3 fibers (duPont FP) and 5 different silicate glass matrices (Corning 9013 and 7740, Owns Illinois N51A and Schott 8229 and 8228) were examined for residual strain and stress in the fibers using x-ray diffraction and the results compared with the predictions of two simple residual stress models. The glasses were chosen to have thermal expansion coefficients ranging from 1.3 to 10.2 x 10-6 /°C, compared with 7.2 x 10-6 /°C for the fiber, so as to produce a range of residual stresses. The magnitudes of the measured normal strains and stresses increased with increasing fiber/matrix thermal expansion mismatch in the order expected except for the sample containing Corning glass 7740 which showed extensive microcracking. Small shear strains were also detected in most of the samples due to the fibers not lying precisely along the presumed uniaxial direction. Agreement with the models was qualitative only but revealed that the residual stresses in the samples containing Corning 7740 and Schott 8229 glasses were substantially less than expected, possibly due to microcracking and/or fiber degradation.