Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography.
Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography.
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DOI：
10.1016/j.dental.2007.08.001
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发表时间：
2008-05
期刊：
影响因子：
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通讯作者：
B. Taskonak;J. Griggs;J. J. Mecholsky-J.;Jiahau Yan
中科院分区：
文献类型：
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作者：
B. Taskonak;J. Griggs;J. J. Mecholsky-J.;Jiahau Yan
目的本研究的目的是检验这样的假设：牙科陶瓷样本的弯曲强度和临界缺陷尺寸将受到测试环境和应力率的影响，即使它们的断裂韧性值保持不变。方法陶瓷样本由铝瓷（Vitadur Alpha; VITA Zahnfabrik，Bad Säckingen，德国）和 氧化铝-氧化锆-玻璃复合材料（In-Ceram®Zirconia；VITA Zahnfabrik）。根据 ISO 6872 标准，制作了 300 个单轴弯曲样本（每种材料 150 个），尺寸为 25mm×4mm×1.2mm。每组 30 个样本均使用四种不同目标应力速率之一在水中断裂，其对数范围为 Vitadur Alpha 的 0.1 至 100MPa/s，In-Ceram®Zirconia 的对数范围为 0.01 至 10MPa/s。第五组在惰性环境（油）中进行测试，Vitadur Alpha 的目标应力率为 100MPa/s，In-Ceram®Zirconia 的目标应力率为 1000MPa/s。通过 Kruskal-Wallis 单向方差分析对应力率和环境对弯曲强度、临界缺陷尺寸和断裂韧性的影响进行统计分析，然后使用 Dunn 检验 (α=0.05) 进行事后比较。此外，还制作了 20 个具有受控缺陷的 Vitadur Alpha 样本，以简化断口分析。这些样本一半在水中进行断裂测试，一半在油中进行断裂测试，目标应力率为 100MPa/s，并使用曼-惠特尼秩和检验（α=0.05）对结果进行比较。使用对数回归模型确定每种材料的疲劳参数。 结果对于每种陶瓷成分，在油中测试的样本比在水中测试的样本具有显着更高的强度（P≤0.05）和更小的临界缺陷尺寸（对于 Vitadur Alpha 显着，P≤0.05），但断裂韧性没有显着差异（P>0.05）。在较快的应力速率下测试的样品具有显着更高的强度（P≤0.05），但断裂韧性没有显着差异（P>0.05）。关于临界缺陷尺寸，应力速率对 In-Ceram®Zirconia 样品有显着影响 (P≤0.05)，但对 Vitadur Alpha 样品没有显着影响 (P>0.05)。 Vitadur Alpha 的疲劳参数 n 和 lnB 分别为 38.4 和 −12.7，In-Ceram®Zirconia 分别为 13.1 和 10.4。 意义 水分辅助的亚临界裂纹扩展对 In-Ceram®Zirconia 核心陶瓷的有害影响比对 Vitadur Alpha 陶瓷的有害影响更大。断裂表面分析确定了断裂表面特征，这些特征可能会误导调查人员错误地识别关键缺陷。
OBJECTIVESThe aim of this study was to test the hypothesis that the flexural strengths and critical flaw sizes of dental ceramic specimens will be affected by the testing environment and stressing rate even though their fracture toughness values will remain the same.METHODSCeramic specimens were prepared from an aluminous porcelain (Vitadur Alpha; VITA Zahnfabrik, Bad Säckingen, Germany) and an alumina–zirconia–glass composite (In-Ceram®Zirconia; VITA Zahnfabrik). Three hundred uniaxial flexure specimens (150 of each material) were fabricated to dimensions of 25mm×4mm×1.2mm according to the ISO 6872 standard. Each group of 30 specimens was fractured in water using one of four different target stressing rates ranging on a logarithmic scale from 0.1 to 100MPa/s for Vitadur Alpha and from 0.01 to 10MPa/s for In-Ceram®Zirconia. The fifth group was tested in inert environment (oil) with a target stressing rate of 100MPa/s for Vitadur Alpha and 1000MPa/s for In-Ceram®Zirconia. The effects of stressing rate and environment on flexural strength, critical flaw size, and fracture toughness were analyzed statistically by Kruskal–Wallis one-way ANOVA on ranks followed by post hoc comparisons using Dunn's test (α=0.05). In addition, 20 Vitadur Alpha specimens were fabricated with controlled flaws to simplify fractography. Half of these specimens were fracture tested in water and half in oil at a target stressing rate of 100MPa/s, and the results were compared using Mann–Whitney rank sum tests (α=0.05). A logarithmic regression model was used to determine the fatigue parameters for each material.RESULTSFor each ceramic composition, specimens tested in oil had significantly higher strength (P≤0.05) and smaller critical flaw size (significant for Vitadur Alpha, P≤0.05) than those tested in water but did not have significantly different fracture toughness (P>0.05). Specimens tested at faster stressing rates had significantly higher strength (P≤0.05) but did not have significantly different fracture toughness (P>0.05). Regarding critical flaw size, stressing rate had a significant effect for In-Ceram®Zirconia specimens (P≤0.05) but not for Vitadur Alpha specimens (P>0.05). Fatigue parameters, n and lnB, were 38.4 and −12.7 for Vitadur Alpha and were 13.1 and 10.4 for In-Ceram®Zirconia.SIGNIFICANCEMoisture assisted subcritical crack growth had a more deleterious effect on In-Ceram®Zirconia core ceramic than on Vitadur Alpha porcelain. Fracture surface analysis identified fracture surface features that can potentially mislead investigators into misidentifying the critical flaw.