FM-DBEM Simulation of 3D Microvoid and Microcrack Graphite Models

Houdi Lu,Yu Zhou,Lie Jin,Haitao Wang,Hongtao Wang,Xinxin Wu

doi:10.1155/2017/1071709

Abstract

The graphite is porous medium, and the geometry and size distribution of its structural deficiencies such as microcracks and microvoids at different oxidation degrees have a great influence on the overall performance. In this paper, we adopt the FM-DBEM to study 3D models which contain spheroidal microvoids and circular microcracks. The accuracy of this method is tested by a comparison to the theoretical solution to the problem of 2D microcrack and microvoid interaction problem. Two simulations are conducted: the simulation of graphite model containing a large number of randomly distributed microcracks and microvoids and the simulation of graphite model containing microcracks and growing microvoids. The simulations investigate the effective moduli versus the two microstructures’ density and the effect of microvoid’s growth on the SIF of microcrack.

Highlights

Nuclear graphite is widely used as fuel blocks and reactor internals in high-temperature gas-cooled reactors (HTR) because of its high-temperature resistance and neutron moderation [1, 2]
This paper adopted the 3D FM-dual boundary element method (DBEM) to simulate the graphite model containing a large quantity of microvoids and microcracks
By the simulation under the approximate 3D equivalent plane strain state and the comparison to several existing theoretical approximate solutions, we have ensured the effectiveness and accurateness of the solver and proved that a result with high precision can be guaranteed by using this fast multipole-dual boundary element method (FM-DBEM) to simulate the structural model containing microvoids and microcracks

Summary

Introduction

Nuclear graphite is widely used as fuel blocks and reactor internals in high-temperature gas-cooled reactors (HTR) because of its high-temperature resistance and neutron moderation [1, 2]. The local behavior of such defective material has been studied by many other researchers [9,10,11,12] using theoretical approaches, but the theoretical solutions are obtained for simple cases, such as a void among several regularly spaced cracks or a crack among several regularly spaced voids embedded in an infinite plate subjected to remote loading Another characteristic of graphite is its anisotropy. Many researchers [27,28,29,30] have adopted the fast multipole method (FMM) (Rokhlin [31]) in their BEM because of FMM’s ability to reduce memory requirement and calculation scale Another fast algorithm widely adopted for crack problems is hierarchical matrices. It can be applied to simulate complex structures and components containing microvoids and microcracks

Models and Methods

Results and Discussion

Conclusions