Characterization on crack propagation of nuclear graphite under three-point bending

Abstract

Abstract The fracture properties of graphite produced in China, named as CLG, were studied by performing three-point bending tests on center-notched beams. The load-deflection (P-δ) curves and load-crack mouth opening displacement (P-CMOD) curves of the beams in the entire loading process were obtained. Electronic speckle pattern interferometry (ESPI) technique was used to measure the full-field displacement of the beams. Through analysis on the relationship between the δ and CMOD, the δ-CMOD curves were divided into nonlinear and linear parts, and its turning point corresponded approximately to the post-peak load of 55% Pmax. By curve fitting, empirical formulas were established for the δ-CMOD relationships. In addition, crack evolution rules were evaluated based on the relationship of crack opening displacement (COD) versus crack length a of specimen CLG-1 at 14 loading levels. Through piecewise analysis, it could be found that linear elastic fracture mechanics were applicable to determine the COD along the whole crack path before the peak load. Therefore, new formulas were proposed to estimate the COD-a relationship for the entire loading process. Furthermore, the COD-a curves of other specimens in the same batch with CLG-1 were calculated by using the present formulas and compared with the experimental results. Excellent agreement was observed, which validates the reliability of the present formulas.