Effects of specimen size on the flexural strength and Weibull modulus of nuclear graphite IG-110, NBG-18, and PCEA

Abstract

Changes in flexural strength and Weibull modulus due to specimen size were investigated for three nuclear graphite grades, IG-110, NBG-18, and PCEA, using four-point-1/3 point (4-1/3) loading with specimens of three different sizes: 3.18 (Thickness)×6.35 (Width)×50.8 (Length), 6.50(T)×12.0(W)×52.0(L), 18.0(T)×16.0(W)×64(L) (mm) (total: 210 specimens). Results showed some specimen size effects were grade dependent: While NBG-18 (a) showed rather significant specimen size effects (37% difference between the 3T and 18T), the differences in IG-110 and PCEA were 7.6–15%. The maximum differences in flexural strength due to specimen size were larger in the PCEA and NBG-18 having larger sized coke particles (medium grain size: >300μm) than the IG-110 with super fine coke particle size (25μm). The Weibull modulus showed a data population dependency, in that it decreased with increasing numbers of data used for modulus determination. A good correlation between the fracture surface roughness and the flexural strength was confirmed.