Fraunhofer Institute for Ceramics Technologies and Systems IKTS, Michael-Faraday-Str. 1, 07629 Hermsdorf, Germany.
University Hospital Tübingen, Section "Medical Materials Science & Technology", Osianderstr. 2-8, 72076 Tuebingen, Germany.
Dent Mater. 2022 Jul;38(7):1128-1139. doi: 10.1016/j.dental.2022.05.001. Epub 2022 May 23.
This interlaboratory round robin test investigated the robustness of the Chevron-Notch Beam (CNB) test method and the effect of the processing and testing variations on the fracture toughness of a dental 3Y-TZP ceramic.
The round robin test was performed precisely following the procedures recommended in ISO 24370:2005 and applied on a commercial 3Y-TZP ceramic (product information). A total of 335 test specimens with dimensions 3×4 x 45 mm³ was equally distributed among 10 participating laboratories of varying experience in fracture toughness testing. A standard operating procedure was defined with either narrow processing tolerances or alternative (wider) processing tolerances (as proposed in ISO 24370). Fracture toughness data (series 2) was analyzed using one way ANOVA followed by post hoc Tukey HSD test and 95% Confidence Intervals (CI) were computed (p < 0.05). A further, preceding round-robin (series 1) test was conducted with - more possible variations of test conditions regarding CNB notch processing and storage conditions. Those results are summarized in the supplement and discussed with the actual ISO 24370 test.
Fracture toughness of the 3Y-TZP ceramic material, summarized over all laboratories was measured to K = 4.48 ± 0.11 MPam for the standard processing tolerance and K = 4.55 ± 0.31 MPam for the alternative tolerance. The results revealed a significant influence of cutting offset and notch geometry on K when using CNB method. The test medium also has a significant influence on K in terms of reduced fracture toughness under the influence of water. With defined testing conditions the number of valid tests and reduced standard deviation increased. In case of strictly following such standard operation procedures, K can be determined with high reliability. There is no difference between the involved laboratories, but significant influence of cutting offset on K was observed.
The CNB method is suitable method for determination of K on fine-grained ceramics such as 3Y-TZP ceramic. By using tighter tolerances for processing and testing, i.e. closely following the ISO 24370 procedure, a highly-precise evaluation of fracture toughness with low data variation is achievable. The information of the storage medium should always be reported along with the data. CNB fracture toughness testing is an alternative method compared to Single-edge V-notch beam (SEVNB), especially for fine-grained ceramics.
本实验室间协作研究旨在探究 Chevron-Notch Beam (CNB) 测试方法的稳健性，以及加工和测试变化对牙科 3Y-TZP 陶瓷断裂韧性的影响。
协作研究严格按照 ISO 24370:2005 中的程序进行，并应用于商用 3Y-TZP 陶瓷（产品信息）。共有 335 个尺寸为 3×4 x 45mm³ 的测试样本，由 10 个具有不同断裂韧性测试经验的参与实验室平均分配。定义了一个标准操作程序，其中包括窄加工公差或替代（更宽）加工公差（如 ISO 24370 中所建议的）。使用单因素方差分析（ANOVA）分析断裂韧性数据（系列 2），然后进行事后 Tukey HSD 检验，并计算 95%置信区间（CI）（p<0.05）。在此之前，进行了一轮实验室间协作研究（系列 1），其中涉及 CNB 缺口加工和存储条件的更多可能测试条件变化。这些结果总结在补充材料中，并与实际的 ISO 24370 测试一起讨论。
在所有实验室中，3Y-TZP 陶瓷材料的断裂韧性总结为标准加工公差下的 K=4.48±0.11MPa·m，替代公差下的 K=4.55±0.31MPa·m。结果表明，使用 CNB 方法时，切割偏移和缺口几何形状对 K 有显著影响。测试介质也对 K 有显著影响，在水的影响下，断裂韧性降低。在定义了测试条件的情况下，有效测试的数量和标准偏差的降低都增加了。在严格遵循这种标准操作程序的情况下，可以可靠地确定 K。参与实验室之间没有差异，但观察到切割偏移对 K 有显著影响。
CNB 方法适用于测定 3Y-TZP 等细晶粒陶瓷的 K 值。通过对加工和测试使用更严格的公差，即严格遵循 ISO 24370 程序，可以实现具有低数据变化的高精确断裂韧性评估。应始终随数据报告存储介质的信息。与单边 V 型缺口梁（SEVNB）相比，CNB 断裂韧性测试是一种替代方法，特别是对于细晶粒陶瓷。
