Department of Dental Materials, University of São Paulo, Av. Prof. Lineu Prestes, 2227, Cidade Universitária, 05508-000 São Paulo, SP, Brazil.
Dent Mater. 2010 Jan;26(1):83-90. doi: 10.1016/j.dental.2009.09.002.
To evaluate the biaxial and short-beam uniaxial strength tests applied to resin composites based upon their Weibull parameters, fractographic features and stress distribution.
Disk- (15 mm x 1 mm) and beam-shaped specimens (10 mm x 2 mm x 1 mm) of three commercial composites (Concept/Vigodent, CA; Heliomolar/Ivoclar-Vivadent, HE; Z250/3M ESPE, FZ) were prepared. After 48h dry storage at 37 degrees C, disks and beams were submitted to piston-on-three-balls (BI) and three-point bending (UNI) tests, respectively. Data were analyzed by Weibull statistics. Fractured surfaces were observed under stereomicroscope and scanning electron microscope. Maximum principal stress (sigma(1)) distribution was determined by finite element analysis (FEA). Maximum sigma(1-BI) and sigma(1-UNI) were compared to FZ strengths calculated by applying the average failure loads to the analytical equations (sigma(a-BI) and sigma(a-UNI)).
For BI, characteristic strengths were: 169.9a (FZ), 122.4b (CA) and 104.8c (HE), and for UNI were: 160.3a (FZ), 98.2b (CA) and 91.6b (HE). Weibull moduli (m) were similar within the same test. CA and HE presented statistically higher m for BI. Surface pores (BI) and edge flaws (UNI) were the most frequent fracture origins. sigma(1-BI) was 14% lower than sigma(a-BI). sigma(1-UNI) was 43% higher than sigma(a-UNI).
Compared to the short-beam uniaxial test, the biaxial test detected more differences among composites and displayed less data scattering for two of the tested materials. Also, biaxial strength was closer to the material's strength estimated by FEA.
通过 Weibull 参数、断口形貌特征和应力分布来评估双轴和短梁单轴强度测试在树脂复合材料中的应用。
制备三种商用复合材料（Concept/Vigodent，CA；Heliomolar/Ivoclar-Vivadent，HE；Z250/3M ESPE，FZ）的圆盘（15mm×1mm）和梁形试件（10mm×2mm×1mm）。在 37°C 下干燥储存 48 小时后，分别对圆盘和梁进行活塞三点球（BI）和三点弯曲（UNI）测试。数据通过 Weibull 统计进行分析。用立体显微镜和扫描电子显微镜观察断口形貌。通过有限元分析（FEA）确定最大主应力（sigma(1)）分布。比较最大 sigma(1-BI)和 sigma(1-UNI)与应用平均失效载荷到分析方程（sigma(a-BI)和 sigma(a-UNI)）计算的 FZ 强度。
BI 时，特征强度分别为：169.9a（FZ）、122.4b（CA）和 104.8c（HE），UNI 时，强度分别为：160.3a（FZ）、98.2b（CA）和 91.6b（HE）。同一测试中，Weibull 模数（m）相似。BI 时，CA 和 HE 的 m 统计上更高。表面孔隙（BI）和边缘缺陷（UNI）是最常见的断裂起源。sigma(1-BI)比 sigma(a-BI)低 14%。sigma(1-UNI)比 sigma(a-UNI)高 43%。
与短梁单轴试验相比，双轴试验在两种测试材料中检测到复合材料之间更多的差异，并且数据分散性更小。此外，双轴强度更接近有限元分析（FEA）估计的材料强度。
