Slow crack growth in ceramic materials at elevated temperatures

1975 ◽  
Vol 6 (4) ◽  
pp. 707-716 ◽  
Author(s):  
A. G. Evans ◽  
L. R. Russell ◽  
D. W. Richerson
Keyword(s):  
Crack Growth ◽  
Elevated Temperatures ◽  
Slow Crack Growth ◽  
Ceramic Materials

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.

Probabilistic Design and Reliability of Silicon Carbide Ceramics

1982 ◽  
Vol 104 (3) ◽  
pp. 635-642 ◽  
Author(s):  
M. Srinivasan ◽  
S. G. Seshadri
Keyword(s):  
Silicon Carbide ◽  
Crack Growth ◽  
Elevated Temperatures ◽  
Ceramic Materials ◽  
Material Behavior ◽  
Evaluation Methodology ◽  
Probabilistic Design ◽  
Proof Testing ◽  
Risk Of Rupture ◽  
Silicon Carbide Ceramics

Ceramic materials generally lack ductility and toughness, and exhibit variability in properties. In order to design with ceramic materials, the variation in material properties, especially strength, has to be statistically analyzed for reliability. Conventional design can be done with calculations utilizing safety factors. However, modern design aspects include proof testing and appropriate nondestructive evaluation methodology. Possible microstructural changes which occur during proof testing may influence subsequent material behavior and must be included in the design methodology. The temperature dependence of flexural strength of two engineering structural ceramics—single-phase sintered alpha silicon carbide and two-phase fine grain reaction-bonded silicon carbide—are examined. Using Weibull statistics, the risk of rupture for various stress levels has been derived from flexural versus tensile strength relationships. Ceramic life prediction considers subcritical crack growth and strength degradation in service environments. The slow crack growth possibilities at elevated temperatures for sintered alpha silicon carbide are examined in dynamic stressing rate and stress rupture experiments. Crack arrest and crack propagation resistance during proof testing and their implications in the probabilistic design with ceramics are analyzed.

Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading: Commonality of Slow Crack Growth in Advanced Ceramics

2014 ◽  
Author(s):  
Sung R. Choi ◽  
D. Calvin Faucett ◽  
Brenna Skelley
Keyword(s):  
Crack Growth ◽  
Glass Ceramic ◽  
Life Prediction ◽  
Elevated Temperatures ◽  
Slow Crack Growth ◽  
Static Fatigue ◽  
Fatigue Data ◽  
Prediction Approach ◽  
Applied Stresses ◽  
Dynamic Fatigue

An extensive experimental work for Pyroceram™ 9606 glass-ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6 to 1.9 with an average of msf = 1.7±0.2. A life prediction using the previously-determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack-growth formulation was operative, a commonality of slow crack growth in these materials systems.

The Development of Life Prediction Techniques for Structural Ceramics

1996 ◽  
Vol 118 (4) ◽  
pp. 847-855
Author(s):  
P. K. Khandelwal ◽  
N. J. Provenzano ◽  
W. E. Schneider
Keyword(s):  
Crack Growth ◽  
Life Prediction ◽  
High Speed ◽  
Failure Modes ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Department Of Energy ◽  
Bending Stresses ◽  
Prediction Techniques ◽  
Fast Fracture

One of the major challenges involved in the use of ceramic materials in advanced vehicular heat engines is ensuring adequate strength and durability. This Department of Energy supported activity has developed methodologies to predict the structural behavior of ceramic components. The effort involved the characterization of injection-molded and hot isostatic pressed PY6 silicon nitride and the development of analytical life prediction techniques. Three failure modes are addressed: fast fracture, slow crack growth, and creep rupture. The technique deals with surface as well as internal component failures. The life prediction methodologies for fast fracture and slow crack growth have been verified using two types of confirmatory specimens: (1) flat circular disks subjected to bending stresses, and (2) high-speed rotating spin disks. Correlation was achieved for a variety of test conditions and failure mechanisms. The predictions associated with surface failures proved to be optimistic, requiring re-evaluation of the components’ initial fast fracture strength. Correlation was achieved for the spin disks that failed in fast fracture from internal flaws. Time-dependent, elevated-temperature spin disk failures were also successfully predicted.

Slow Crack Growth of a Pyroceram Glass Ceramic Under Static Fatigue Loading—Commonality of Slow Crack Growth in Advanced Ceramics

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Sung R. Choi ◽  
D. Calvin Faucett ◽  
Brenna Skelley
Keyword(s):  
Crack Growth ◽  
Glass Ceramic ◽  
Life Prediction ◽  
Elevated Temperatures ◽  
Slow Crack Growth ◽  
Static Fatigue ◽  
Fatigue Data ◽  
Prediction Approach ◽  
Applied Stresses ◽  
Dynamic Fatigue

An extensive experimental work for Pyroceram™ 9606 glass–ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20–23 test specimens used at each of four applied stresses. The slow crack growth (SCG) parameters n and D were found to be n = 19 and D = 45 with a coefficient of correlation of rcoef = 0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6–1.9 with an average of msf = 1.7 ± 0.2. A life prediction using the previously determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites (CMCs) based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack growth formulation was operative, a commonality of SCG in these materials systems.

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