D. Chen et al., In situ measurement of fatigue crack growth rates in a silicon carbide ceramic at elevated temperatures using a DC potential system, J TEST EVAL, 28(4), 2000, pp. 236-241
The understanding of the mechanisms of fatigue-crack propagation in advance
d ceramics at elevated temperatures (>800 degrees C) has in part been hampe
red by the experimental difficulty in directly measuring crack lengths, and
hence crack growth rates, at such high temperatures. In this study, we sho
w how the direct-current (DC) electrical-potential technique, which has bee
n used for such measurements in metallic materials for over 30 years, can b
e successfully utilized to monitor fatigue crack growth rates in situ in a
silicon carbide ceramic at temperatures between 850 and 1300 degrees C, bec
ause of the electrical conductivity in SiC at these temperatures. In additi
on to providing a highly efficient means of collecting such data, this appr
oach offers several significant advantages over the techniques that have be
en used to date for advanced ceramics, particularly in avoiding artifacts d
ue to thermal fatigue and oxidation from repeated exposure to air and/or lo
wer temperatures while making measurements. Effects of parameters such as l
oad ratio and loading frequency are examined, both on crack growth behavior
and the accuracy of measurement. With appropriate considerations, electric
al-potential calibrations determined at ambient temperatures in metallic ma
terials can be applied readily to elevated temperature measurements in sili
con carbide.