| 0449 Determining the Slow Crack Growth Parameters of Bilaminate Disks by Constant Displacement-Rate Flexural Testing | ||
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G.A. THOMPSON, US Army Dental Research Detachment, Great Lakes, IL, USA Mechanical property data regarding slow crack growth (SCG) of dental ceramics or glasses is limited, even though this effect may be considerable. Slow crack growth parameters have been estimated for only a few commercial dental ceramics and glasses; however, no one has investigated layered structures and how changes in relative layer heights (RLH) may affect parameter estimates. Objectives: This study examined the influence of RLH's of bilayered ceramic composite disks composed of In-Ceram Alumina and Vitadur Alpha porcelain on the SCG exponent. Methods: Disks were fabricated with RLH's of 1:2, 1:1, and 2:1, for In-Ceram Alumina and Vitadur Alpha porcelain, respectively. Ninety specimens each (thirty 1:2, thirty 1:1, and thirty 2:1) were tested in an equibiaxial ring-on-ring testing apparatus at displacement rates of 0.127, 1.27 and 12.7 mm/min. Number of specimens tested was 267. Results: Linear regression analysis of log flexure stress vs. log displacement rate plots of RLH 1:2, 1:1 and 2:1 resulted in SCG parameters of 13.6 (10.8, 17.0); 34.7 (23.6, 66.0) and 22.0 (13.8, 50.3), respectively. 95% double confidence bounds are in parentheses. Confidence bounds of RLH 1:1 did not overlap with the confidence bounds of RLH 1:2 and they are statistically significantly different; however, RLH 2:1 was not statistically significantly different from RLH 1:2 or RLH 1:1. Eighty-nine specimens exhibited multi-stage failure modes. Of these specimens, 8 were from RLH 1:2; 46 from RLH 1:1; and 38 from RLH 2:1. Fifty-two multi-stage failures occurred at the 0.127 mm/min displacement rate, 8 at 1.27 mm/min, and 29 at 12.7 mm/min. Multi-stage failures usually exhibited a fall, followed by a rise in load prior to failure, and most occurred in specimens with thicker cores at low displacement rates. Conclusions: Multi-stage failure processes effectively increased the SCG parameters of RLH 1:1 and 2:1 because initial cracks were not catastrophic.
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| Seq #65 - Ceramics: Strength and Fracture Analysis 1:45 PM-3:45 PM, Thursday, 13 March 2003 Henry B. Gonzalez Convention Center Room 206A | ||
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