Analysis of dynamic fracture and fragmentation of graphite bricks by combined XFEM and cohesive zone approach

摘要

It has been anticipated and recently observed that axial cracks can occur at keyway corners of graphite bricks in the UK Advanced Gas-cooled Reactors (AGR). The crack initiation is triggered by internal stress reversal during reactor operation and may potentially lead to brick more cracks through a mechanism known as Prompt Secondary Cracking (PSC). To assess the likelihood of this occurring, a method for modelling dynamic fracture, known as eXtended Finite Element Method with cohesive elements (XCZM), is used to analyse whole 3D component fragmentation. XCZM is used here to model primary crack interactions with a methane hole, the effect of graphite heterogeneity, and secondary crack profiles in a 3D brick slice under external hoop stress loading. The results show that methane holes in bricks can be beneficial for brick integrity, as these can lead to crack path deflection with associated increase of dissipated energy. Further, the results suggest that graphite heterogeneity does not affect significantly the crack profile and therefore the integrity assessment. Finally, it is demonstrated that PSC may readily occur and the secondary crack propagates towards regions of high kinetic energy.