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Study on Failure Mechanism and Lifetime for Dental Porcelain

烤瓷牙失效机理及寿命研究

基本信息

批准号：
02670880
负责人：
GOTO Takayasu
金额：
$ 1.34万
依托单位：
Asahi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

This study has been made to predict a fatigue life and to clarify a mechanism of fatigue failure on porcelain -fused-to-metal (PFM). The dynamic fatigue test in the four point bending mode was performed at five different strain rates, 8.33x10^<-x> (x=2, 3, 4, 5, 6) sec^<-1> in distilled water at 37ﾟC. To confirm a subcritical crack growth in water, the four point bending strength and critical stress intensity factor in Ar gas (dry condition) at 37ﾟC were measured. Furthermore, the elastic costants measurement was carried out to get the fracture energy.The weibull parameters resulted from dynamic fatigue test at five strain rates were in the range of 15 to 18. Because of their small standard deviations, the fracture mode was regarded to be expressed by a single weibull mode. The fatigue parameter given from this test was estimated at n=35.3<plus-minus>0.8. Although this value is not so small compared with other ceramics, the present PFM indicates to take place the subcritical crack growth by stress corrosion in the presence of wateBy using the fatigue parameter, fracture stress and time-to-failure data, the SPT (Strength-Probability-Time) diagram was obtained and it gave- a conclusion, as an example, that the stress less than 21 MPa would assure 20 years in lifetime with the survival probability of 99.9 %.The average strength in Ar gas was 23 % larger than that in water, but the weibull parameter was small. Using both these strength data and critical stress intensity factor, th ratio crack length in water and Ar gas just before failure was found to be 1.3 to 2.3. This result indicates that PFM takes place the subcritical crack growth in water.The fracture energy calculated was 6600 erg/cm^2. This value is considered to be small in water because this calculated energy is regarded to be critical fracture energy. The further interesting finding by the scanning electron micrograph observation is that PFM produced the striation pattern like a metal.

本研究旨在预测烤瓷熔附金属（PFM）的疲劳寿命，并阐明其疲劳失效机理。在5种不同的应变速率下，在37 ℃的蒸馏水中，以8.33x10^<-x>（x=2、3、4、5、6）sec^<-1>，进行四点弯曲模式下的动态疲劳试验。为了确认水中的亚临界裂纹扩展，在37 ℃的Ar气（干燥条件）中测量了四点弯曲强度和临界应力强度因子。在此基础上，通过弹性常数的测量，得到了断裂能的分布规律，在五种应变率下的动态疲劳试验得到的威布尔参数在15 ~ 18之间。由于它们的标准差很小，断裂模式被认为是由一个单一的威布尔模式表示。本试验给出的疲劳参数估计为n=35.3 <plus-minus>0.8。虽然该值与其它陶瓷相比并不小，但本发明的PFM在有水存在下发生了应力腐蚀亚临界裂纹扩展。（强度-概率-时间）图，并给出了一个结论，作为一个例子，当应力小于21 MPa时，可保证20年的寿命，其存活概率为99.9%，Ar气中的平均强度比水中的平均强度高23%，但Weibull参数较小。使用这些强度数据和临界应力强度因子，th比裂纹长度在水和氩气刚刚失败之前被发现是1.3至2.3。结果表明，金属烤瓷在水中发生亚临界裂纹扩展，断裂能为6600 erg/cm ^2。该值在水中被认为是小的，因为该计算的能量被认为是临界断裂能。通过扫描电子显微镜观察的进一步有趣的发现是，PFM产生类似金属的条纹图案。