The ever-increasing usage of ceramic materials in restorative dentistry necessitates a simple and effective method to evaluate flexural strength σF and fracture toughness KC. We propose a novel method to determine these quantities using a bilayer specimen composed of a brittle plate adhesively bonded onto a transparent polycarbonate substrate. When this bilayer structure is placed under spherical indentation, tunneling radial cracks initiate and propagate in the lower surface of the brittle layer. The failure analysis is based on previous theoretical relationships, which correlate σF with the indentation force P and layer thickness d, and KC with P and mean length of radial cracks. This work examines the accuracy and limitations of this approach using a wide range of contemporary dental ceramic materials. The effect of layer thickness, indenter radius, load level, and length and number of radial cracks are carefully examined. The accuracy of the predicted σF and KC is similar to those obtained with other concurrent test methods, such as biaxial flexure and 3-point bending (σF), and bending specimens with crack-initiation flaws ( KC). The benefits of the present approach include treatment for small and thin plates, elimination of the need to introduce a precrack, and avoidance of dealing with local material nonlinearity effects for the KC measurements. Finally, the bilayer configuration resembles occlusal loading of a ceramic restoration (brittle layer) bonded to a posterior tooth (compliant substrate).

中文翻译：

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测量牙科陶瓷韧性和强度的双层方法


陶瓷材料在牙科修复中的使用不断增加，需要一种简单有效的方法来评估弯曲强度 σF 和断裂韧性 KC。我们提出了一种新方法来确定这些量，使用由粘合到透明聚碳酸酯基材上的脆性板组成的双层样本。当这种双层结构放置在球形压痕下时，隧道径向裂纹在脆性层的下表面开始并扩展。失效分析基于先前的理论关系，其中 σF 与压痕力 P 和层厚度 d 相关，KC 与 P 和径向裂纹的平均长度相关。这项工作使用多种当代牙科陶瓷材料检验了这种方法的准确性和局限性。仔细检查层厚度、压头半径、载荷水平以及径向裂纹的长度和数量的影响。预测的 σF 和 KC 的精度与其他并行测试方法（例如双轴弯曲和三点弯曲 (σF) 以及带有裂纹萌生缺陷的弯曲样本 (KC)）获得的精度相似。本方法的优点包括处理小板和薄板、消除引入预裂纹的需要以及避免处理 KC 测量的局部材料非线性效应。最后，双层结构类似于粘合到后牙（顺应性基底）的陶瓷修复体（脆性层）的咬合载荷。