Department of Biomedical Materials Science, University of Mississippi Medical Center, 2500 North State Street, Room D528, Jackson, MS 39216-4505, USA.
Dent Mater. 2011 Apr;27(4):364-70. doi: 10.1016/j.dental.2010.11.016. Epub 2010 Dec 17.
To more efficiently determine the subcritical crack growth (SCG) parameters of dental ceramics, the effects of stressing rate and choice of statistical regression model on estimates of SCG parameters were assessed.
Two dental ceramic materials, a veneering material having a single critical flaw population (S) and a framework material having partially concurrent flaw populations (PC), were analyzed using constant stress-rate testing, or "dynamic fatigue", with a variety of testing protocols. For each material, 150 rectangular beam specimens were prepared and tested in four-point flexure according to ISO6872 and ASTM1368. A full-factorial study was conducted on the following factors: material, stress rate assumed vs. calculated, number of stress rates, and statistical regression method.
The proportion of specimens for which the statistical models over-estimated reliability was not significantly different based on regression method for Material S (P = 0.96, power = 94%) and was significantly different based on regression method for Material PC (P < 0.001). The standard method resulted in SCG parameters, n and l nB, of 35.9 and -11.1 MPa(2)s for Material S and 12.4 and 9.61 MPa(2)s for Material PC, respectively.
The method of calculation that uses only the median strength value at each stress rate provided the most robust SCG parameter estimates. Using only two stress rates resulted in fatigue parameters comparable to those estimated using four stress rates having the same range. The stress rate of each specimen can be assumed to be the target stress rate with negligible difference in SCG parameter estimates.
为了更有效地确定牙科陶瓷的亚临界裂纹扩展 (SCG) 参数，评估了加荷速率和统计回归模型选择对 SCG 参数估计的影响。
使用恒应变速率测试（即“动态疲劳”），结合多种测试方案，对具有单一临界缺陷群体（S）的贴面材料和具有部分并发缺陷群体（PC）的框架材料这两种牙科陶瓷材料进行了分析。对于每种材料，根据 ISO6872 和 ASTM1368 标准，用 150 个矩形梁试件制备并进行四点弯曲试验。对以下因素进行了完全析因研究：材料、假设的与计算的应变速率、应变速率的数量和统计回归方法。
对于材料 S，基于回归方法的试件比例没有因统计模型高估可靠性而显著不同（P = 0.96，功效为 94%），而对于材料 PC，则因回归方法而显著不同（P < 0.001）。标准方法得出的 SCG 参数 n 和 l nB 分别为材料 S 的 35.9 和-11.1 MPa(2)s，以及材料 PC 的 12.4 和 9.61 MPa(2)s。
仅使用每个应变速率的中值强度值进行计算的方法提供了最稳健的 SCG 参数估计。使用仅两个应变速率可以得到与使用具有相同范围的四个应变速率得到的疲劳参数相当的结果。每个试件的应变速率可以假定为目标应变速率，对 SCG 参数估计的影响可以忽略不计。
