Reliable Ceramic Structural Composites Designed with a Threshold Strength
Technical rept. for 1 May 2000-30 Apr 2001
CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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Compressive layers, placed within a laminate, can arrest cracks. With an increasing applied stress, the arrested crack can propagate through the compressive layer. These phenomena produce a material with a threshold strength, i.e., failure can not occur below a critical stress. A previously reported stress intensity function describes different variables, e.g., magnitude of compressive stress, thickness of compressive layer, distance between compressive layers, that govern the threshold strength. Laminar composites composed of thicker alumina layers separated by thinner aluminamullite layers were fabricated to test the different variables that were predicted to govern the threshold strength. It is shown that the data agree well with the predicted values only when the magnitude of the compressive stress andor the thickness of the compressive stress were low. For these conditions, the crack extended straight through the compressive layers as assumed by the model used to predict the threshold strength. On the other hand, when the compressive stress andor the layer thickness were large the threshold strength was larger than the predicted value. In addition, for these conditions the crack bifurcated through the compressive layer. The angel between the bifurcated cracks increased with increasing compressive stress.
- Ceramics, Refractories and Glass