Biaxial strength and fracture criterion for HTGR graphites

Abstract

The strength and fracture criterion at the biaxial stress state were examined for two grades of HTGR graphites, a fine-grained isotropic IG-11 and a medium-grained semi-isotropic PGX. Two types of specimens different in size were tested. The biaxial stress state was realized using a servohydraulic testing machine in combination with an apparatus for applying internal pressure or torque force to a tubular specimen. Main results are: (1) On the basis of the statistical analysis of the data on the smaller IG-11 specimens, the maximum strain energy criterion gave the best fit to the data points both in the first and fourth quadrants of the failure surface. (2) The data on the larger specimens obtained at ORNL fell on the scatter band of the JAERI data, which indicated that no appreciable difference in the biaxial strength of IG-11 graphite was found despite the difference in the test fixture and specimen dimensions. (3) The maximum strain energy criterion was also believed to be most appropriate for PGX graphite for the first quadrant of the failure surface. © 1997 Taylor and Francis Group, Ltd.