Temperature dependence of crack wake bridging stresses in a SiC-whisker-reinforced alumina

The crack face bridging behavior of a SiC-whisker-reinforced alumina composite was characterized between room temperature and 1400 degreesC in air. The bridging relations of the material were deconvoluted from the chevron-notched specimen R-curves by employing the fracture mechanics weight function method and assuming that pullout bridging was the dominant bridging mechanism. The results indicated that the maximum bridging stress decreased linearly with increasing temperature while the distribution of the bridging stresses appeared to shift towards larger crack opening displacements. The former trend was found to be in good agreement with literature data on the temperature dependence of residual stresses measured in similar composites, while the latter agreed with the observation of an increasing whisker pullout length in such composites with increasing temperature. In agreement with previous studies of this material, some crack-tip toughening due to a microcrack damage zone formed around the crack-tip by diffusional cavitation could be observed at T > 1000 degreesC. Although the material exhibited toughening by both a microcrack zone and a bridging zone between 1000 degreesC and 1300 degreesC, no influence from the microcrack zone on the bridging stresses was detected. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.