Arola D, Zheng W, Sundaram N, Rouland J A
Department of Mechanical Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
J Biomed Mater Res A. 2005 May 1;73(2):201-12. doi: 10.1002/jbm.a.30269.
An experimental study of fatigue crack growth in dentin was conducted, and the influence of stress ratio (R) on the crack growth rate and mechanisms of cyclic extension were examined. Double Cantilever Beam (DCB) fatigue specimens were sectioned from bovine molars and then subjected to high cycle fatigue loading (10(5) < N < 10(6)) under hydrated conditions. The evaluation consisted of Mode I loads with stress ratios that ranged from -0.5 to 0.5. The fatigue crack growth rates were measured and used to estimate the crack growth exponent (m) and coefficient (C) according to the Paris Law model. The fatigue crack growth rates for steady-state extension (Region II) ranged from 1E-7 to 1E-4 mm/cycle. It was found that the rate of cyclic extension increased significantly with increasing R, and that the highest average crack growth rate occurred at a stress ratio of 0.5. However, the crack growth exponent decreased with increasing R from an average of 4.6 (R = 0.10) to 2.7 (R = 0.50). The stress intensity threshold for crack growth decreased with increasing R as well. Results from this study suggest that an increase in the cyclic stress ratio facilitates fatigue crack growth in dentin and increases the rate of cyclic extension, both of which are critical concerns in minimizing tooth fractures and maintaining lifelong oral health.
开展了一项关于牙本质疲劳裂纹扩展的实验研究，考察了应力比（R）对裂纹扩展速率及循环扩展机制的影响。从牛磨牙上切割出双悬臂梁（DCB）疲劳试样，然后在水合条件下对其施加高周疲劳载荷（10⁵ < N < 10⁶）。评估包括应力比范围为 -0.5至0.5的I型载荷。测量了疲劳裂纹扩展速率，并根据巴黎定律模型用于估算裂纹扩展指数（m）和系数（C）。稳态扩展（区域II）的疲劳裂纹扩展速率范围为1×10⁻⁷至1×10⁻⁴mm/循环。研究发现，循环扩展速率随R的增加而显著增加，且在应力比为0.5时平均裂纹扩展速率最高。然而，裂纹扩展指数随R的增加而降低，从平均4.6（R = 0.10）降至2.7（R = 0.50）。裂纹扩展的应力强度阈值也随R的增加而降低。本研究结果表明，循环应力比的增加促进了牙本质中的疲劳裂纹扩展并提高了循环扩展速率，这两者都是将牙齿骨折风险降至最低并维持终身口腔健康的关键问题。
