Sr. Choi et Ja. Salem, CRACK-GROWTH RESISTANCE OF IN-SITU-TOUGHENED SILICON-NITRIDE, Journal of the American Ceramic Society, 77(4), 1994, pp. 1042-1046
The fracture toughness of a commercial, hot-pressed, in situ-toughened
silicon nitride with an elongated grain structure is determined by fo
ur different testing methods. The fracture toughness is found to be 5.
76 +/- 0.27, 8.48 +/- 0.50, 10.16 +/- 0.66, and 10.68 +/- 0.39 MPa.m1/
2, respectively, by indentation crack size measurement, indentation st
rength, single-edge-precracked-beam, and chevron-notched-beam methods.
The discrepancy in fracture toughness between the testing methods is
related to R-curve behavior, as measured using the indentation strengt
h technique. These results indicate that there is no unique fracture t
oughness value and that a fracture toughness testing method with appro
priate qualifiers is needed for rising R-curve materials. Therefore, c
are should be taken in interpreting and utilizing fracture toughness v
alues evaluated from different testing methods if a material exhibits
a rising R-curve. Complete characterization of the R-curve may be a pr
erequisite.