R‐Curve Determination for the Initial Stage of Crack Extension in Si3N4

In experimental R-curve investigations crack development usually starts from notches. The validity of R-curves depends on the size of the notch root radius. This influence is ignored in many cases. In this study it will be shown how the notch radius affects the formally computed crack resistance curve and how the initial true R-curve can be obtained from the same data. The tests were performed on a silicon nitride with 5 wt% Y2O3 and 2 wt% MgO. The evaluation of load versus displacement measurements during fracture showed a very steep R-curve with the saturation reached even after about 10 μm crack extension.

[1]  R. M. Cannon,et al.  The Utility of R‐Curves for Understanding Fracture Toughness‐Strength Relations in Bridging Ceramics , 2008 .

[2]  Michael V. Swain,et al.  Measurement of the Total Energy Release Rate for Cracks in PZT Under Combined Mechanical and Electrical Loading , 2007 .

[3]  T. Fett,et al.  Influence of narrow starter notches on the initial crack growth resistance curve of ceramics , 2006 .

[4]  R. M. Cannon,et al.  Fatigue threshold R-curves for predicting reliability of ceramics under cyclic loading , 2005 .

[5]  J. Rödel,et al.  Influence of microcracking on crack-tip toughness of alumina , 2005 .

[6]  G. Schneider,et al.  R‐Curve Behavior and Crack‐Closure Stresses in Barium Titanate and (Mg,Y)‐PSZ Ceramics , 2004 .

[7]  N. Maeda,et al.  In situ measurement of bridging stresses in toughened silicon nitride using Raman microprobe spectroscopy , 2004 .

[8]  J. Rödel,et al.  Crack‐Tip Toughness Measurements on a Sintered Reaction‐Bonded Si3N4 , 2004 .

[9]  D. Munz,et al.  Bridging stresses in sintered reaction-bonded Si3N4 from COD measurements , 2004 .

[10]  T. Fett.  Influence of bridging stresses on specimen compliances , 1996 .

[11]  T. Fett.  Notch effects in determination of fracture toughness and compliance , 1995 .

[12]  D. Marshall,et al.  Crack Resistance Curves in Magnesia‐Partially‐Stabilized Zirconia , 1988 .

[13]  T. Fett,et al.  Determination of the crack-tip toughness in silicon nitride ceramics , 2009 .

[14]  R. Danzer,et al.  Polished notch modification of SENB-S fracture toughness testing , 1997 .

[15]  R. Danzer,et al.  Critical notch-root radius effect in SENB-S fracture toughness testing , 1996 .