Study on Fracture Properties of Nuclear Graphite

Three-point bending tests were performed on the single-edge notched beams made of IG11 graphite to investigate the fracture properties of nuclear graphite. Electronic speckle pattern interferometry（ESPI） technique was used to measure the displacement fields of the graphite beams. Experimental results indicated that the initiation fracture load of graphite beams was 680~838 N and peak load was 845~974 N. At the peak, crack mouth opening displacement was 0.088~0.091 mm, crack tip opening displacement was 0.016~0.018 mm and the crack length was about 25 mm. Furthermore, the initiation fracture toughness and unstable fracture toughness according to the double-K fracture model of concrete were determined as 0.96~1.19 MPa·m^1/2 and 1.61~1.85 MPa·m^1/2 respectively. Elastic modulus was evaluated as 10.22 GPa according to linear elastic fracture mechanics. By analyzing the phase maps at different loading stages, fracture process zone of graphite was identified as square. At the pre-peak stage, the length of the FPZ did not exceed 3 mm; and at the post-peak stage, the length of the FPZ was within 5-8 mm.