Dependence of fracture stress on applied stress rate in a Yb2O3–SiO2-doped hot-pressed silicon nitride ceramic

2001 ◽  
Vol 16 (11) ◽  
pp. 3254-3261 ◽  
Author(s):  
Shuqi Guo ◽  
Naoto Hirosaki ◽  
Yoshinobu Yamamoto ◽  
Toshiyuki Nishimura ◽  
Mamoru Mitomo
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Crack Growth ◽  
Applied Stress ◽  
Fracture Stress ◽  
Fracture Behavior ◽  
Slow Crack Growth ◽  
Silicon Nitride Ceramic ◽  
Temperature Fracture ◽  
Stressing Rate

High-temperature fracture behavior of a Yb2O3–SiO2–doped hot-pressed silicon nitride (Si3N4) ceramic was investigated in four-point flexure between 1000 and 1500 °C at five crosshead speeds, using the specimens precracked with three indentation loads. Above 1000 °C, a temperature and stressing rate dependence of fracture stress was seen. At 1200 °C the fracture stress of the precracked specimens increased with decreasing stressing rates due to a toughening effect, the absence of slow crack growth (SCG). However, at 1400 and 1500 °C the fracture stress decreased with decreasing stressing rate. In particular, this dependence was stronger at 1500 °C than at 1400 °C. The SCG was observed only in the specimens precracked with indentation loads of 98 and 196 N. This crack extended with increasing test temperature and/or decreasing stressing rate. The dependence of fracture stress on stressing rate was attributed to a SCG behavior at higher temperatures.

High-temperature slow crack growth of an Yb2O3–SiO2-doped hot-pressed silicon nitride ceramic

2003 ◽  
Vol 57 (21) ◽  
pp. 3257-3264 ◽  
Author(s):  
Shuqi Guo ◽  
Naoto Hirosaki ◽  
Yoshinobu Yamamoto ◽  
Toshiyuki Nishimura ◽  
Hidehiko Tanaka
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Silicon Nitride Ceramic

scholarly journals Strength Distribution Changes in a Silicon Nitride as a Function of Stressing Rate and Temperature

1998 ◽  
Author(s):  
Andrew A. Wereszczak ◽  
Kristin Breder ◽  
Mark J. Andrews ◽  
Timothy P. Kirkland ◽  
Mattison K. Ferber
Keyword(s):  
Silicon Nitride ◽  
Crack Growth ◽  
Failure Probability ◽  
Life Prediction ◽  
Slow Crack Growth ◽  
Strength Distribution ◽  
Porous Region ◽  
Machining Damage ◽  
Stressing Rate ◽  
Strength Distributions

Machining damage (a surface flaw) and porous-region-flaw (a volume flaw) populations limited the flexure strengths of a commercially available silicon nitride at 25°C, while these same flaws, along with inclusions, limited flexure strengths at 850°C. The machining damage and porous region flaws were the primary interest in the present study because they caused failure at both temperatures. Censoring revealed that the two-parameter Weibull strength distributions representing each flaw population changed as a function of stressing rate (i.e., dynamic fatigue) and temperature. A decrease in the Weibull scaling parameter is recognized as an indication of slow crack growth or time-dependent strength reduction in monolithic ceramics. Available life prediction codes used for reliability predictions of structural ceramic components consider the slow crack growth phenomenon. However, changes in the Weibull modulus are infrequently observed or reported, and typically are not accounted for in these life prediction codes. In the present study, changes in both Weibull parameters for the strength distributions provided motivation to the authors to survey what factors (e.g., residual stress, slow crack growth, and changes in failure mechanisms) could provide partial or full explanation of the observed distribution changes in this silicon nitride. Lastly, exercises were performed to examine the effects of strength distribution changes on the failure probability prediction of a diesel exhaust valve. Because the surface area and volume of this valve were substantially larger than those of the tested bend bars, it was found that the valve’s failure probability analysis amplified some slight or inconclusive distribution changes which were not evident from the interpretation of the censored bend bar strength data.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Sign in / Sign up

Export Citation Format

Share Document