Compressive Surface Layer to Avoid Edge Cracking in Laminar Ceramic Composite
Previous work has shown that layers within ceramic laminates that contain biaxial compressive stresses will also contain tensile stresses where the layer intercepts the surface. It has also been shown that when the thickness of the layer exceeds a critical value, the tensile stresses at and near the surface can produce a centerline crack that extends along the surface to a depth corresponding to the thickness of the compressive layer. The current work explores the concept of preventing the occurrence of surface cracks with a thin layer of material that places the entire external surface in compression. A recent finite element analysis by Monkowski and Beltz showed that when the external surface layer material was identical to the compressive layers, the tensile stresses at the surface could be reduced to zero when the thickness of the surface layer was 0.6 of the thickness of the compressive layer. In addition, they determined the stress intensity factor function for a surface crack and showed that surface cracking could be avoided when the thickness of the surface layer was ≥0.25 times the thickness of the compressive layer. The experimental results presented here show that a thin compressive layer will prevent surface cracks from forming in the compressive layers; the results also appear to confirm the predictions of Monkowski and Beltz.
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Document Type: Research Article
Affiliations: Materials Department, University of California, Santa Barbara, California 93106
Publication date: 2005-10-01