Characterization on tensile behaviors of fracture process zone of nuclear graphite using a hybrid numerical and experimental approach

Abstract

This paper reports an experimental and numerical study on the fracture properties of nuclear graphite NG-CT-01 produced in China. Three-point bending tests were performed on center-notch beams and electronic speckle pattern interferometry (ESPI) technique was employed to measure the full-field deformation of the beams. Besides, finite element analysis was performed by using extended finite element method to simulate the fracture behavior of graphite. Numerical results were compared with the experimental results and excellent agreement was obtained, validating the reliability and accuracy of the numerical model. Based on the strain field measured by ESPI technique, the formation and evolution of the fracture process zone (FPZ) in graphite were observed. The tension softening curve (TSC) of the graphite was determined by using a hybrid numerical and experimental approach. The influences of initial crack length to beam depth ratio on the fracture responses of graphite beam, including the load-displacement curves, double-K fracture parameters, TSCs and the length of the FPZ, were evaluated. In order to explain the correlation between the tension softening behaviors and the fracture mechanism of the FPZ, a tri-linear model was proposed. Furthermore, double-K fracture criterion was employed to predict the crack propagation in graphite.