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VAMAS TWA #3
Project #8: Fracture Toughness of Ceramics Matrix Composites
Round Robin ('94 RRT)
Fracture Toughness IV
Organized by the Japan Fine Ceramic Center, (Dr. Mizuno)

Objective

Evaluate suitability of 3 methods for measuring fracture toughness of ceramic composites.
SEVNB Single Edged "V-Notched" Beam
SENB Single Edged Notched Beam (Saw cut)
SEPB Single Edged Precracked Beam (Bridge-anvil precracked)

Approach

Sintered SiC Whisker - Reinforced Si3N4    "Kryptonite!"
Flexure 3 point 30 or 40 mm span (also 16 mm)
Flexure 4 point 20 x 40 mm
10 specimens by SEPB, remaining 20 with either V (SEVNB) or straight notch (SENB). Use 2 test conditions: different widths or tip radii

Outcome

Completed September 1997; 15 of 16 Laboratories completed the work.

Principal Findings
  • SEPB and SEVNB are suitable for ceramic composites (whisker reinforced).
  • SEPB was accurate and reliable for labs that tested in 3-point flexure loading and that had experience with the method.
  • There was high, unaccounted for variability in SEPB 4-point test results. Many labs continue to have great difficulty precracking SEPB specimens. This is the third VAMAS project that had this outcome!
  • SEPB specimens tested on 16 mm spans produced overestimates of toughness compared with data from longer 30 or 40 mm spans. This outcome was not observed for SEVNB. The problem with the 16 mm spans for SEPB is due to the difficulty of lining up the SEPB precrack with the middle roller.
  • SENB results inevitably overestimated the fracture toughness even for notch widths down to 60 µm.
  • There was a strong correlation of Kc with notch width.
  • SEVNB results converged with, and indeed were slightly lower than, the SEPB results, provided that notch tip radii were < ~20 µm.
  • No consideration of R-curve in this study.
Publications
  1. M. Mizuno and J. Kon, "VAMAS Round Robin on Fracture Toughness Measurement of Ceramic matrix Composite," VAMAS Report #32, JFCC, Nagoya, September, 1997.
  2. M. Mizuno, Y. Nagano, J. Cao, and J. Kon, VAMAS Round Robin on Fracture Toughness Measurement of Ceramic Matrix Composite, CIMTEC 1998.
  3. M. Mizuno, Y. Nagano, J. Kon, H. Tanaka and S. Sakaguchi, "Round Robin on Fracture Toughness Measurement of SiC-Whisker/Si3N4," presented at PACRIM 3, Kyongju, Korea, Sept. 1998.
For more information or copies of the reports, contact:
Dr. Mineo Mizuno, Japan Fine Ceramics Center, 2-4-1 Mutsuno Atsuka-ku, Nagoya, Aichi-ken 456, JAPAN, Tel: +81 (52) 871 3500 email: mizuno@jfcc.or.jp


The VAMAS TWA #3 Round Robins Between 1987 and 1999.

Click on the numbered projects in the image below for round robin details.



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