Energy dissipation during fracturing process of nuclear graphite based on cohesive crack model

Abstract

General consensus in the literature is that the fracturing behavior of nuclear graphite shows a certain degree of nonlinearity due to the presence of a fracture process zone (FPZ) ahead of the crack tip. Thus, it is necessary to take the influence of the FPZ into account when investigating the fracture properties of nuclear graphite. Besides, the energy-based approach has been widely used to characterize the fracturing process in the FPZ. In consideration of all these factors, this paper examines the dissipated energy during the entire fracturing process of local graphite (NG-CT-01) found in China based on the cohesive crack model. The calculation process for estimating the average dissipated energy of the crack growth is obtained through three-point bending tests, which are performed on center-notched graphite beams. Electronic speckle pattern interferometry (ESPI) is used to obtain the full-field deformation of the beams. The experimental and analytical results are then compared, and a satisfactory agreement between the two results are found, which validates the reliability and accuracy of the formulas. The tension softening curves of graphite are plotted and different cohesive laws (bilinear, tri-linear and exponential) are used to determine the average amount of energy consumed during crack extension. The tri-linear softening model is used to evaluate the relationship between the energy dissipation of the fracturing process and the fracture mechanism in the FPZ of the graphite. Furthermore, the energy dissipated during the entire fracturing process of the graphite beam is examined based on three stages: initiation of cracking, propagation of stable cracking and unstable fracturing.