NEUTRON DIFFRACTION STUDY OF CORRELATION BETWEEN REINFORCEMENT SIZE, RESIDUAL STRESS AND MICROCRACKING IN ALUMiNA/SiC_p COMPOSITES

摘要

The thermal residual stresses in alumina/SiC_p composites have been measured as a function of reinforcement size for alumina/20% SiC_p composites. The hydrostatic stress in the particles was ～1200MPa for small SiC particle sizes, but fell abruptly to ～750MPa for particle sizes greater than or equal to 13μm. Microstructural examination showed that this drop in residual stress was caused by spontaneous microcracking of the alumina matrix. The microcracks were in the radial direction relative to the particles and extended fully between the particles. A fracture mechanics model for radial cracks extending from the particles under the action of the tensile residual hoop stress in the matrix deduced from the neutron diffraction measurements was able to predict the critical particle size for cracking, and to explain the abrupt nucleation of microcracking throughout the material.