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T.-T.-G. Vo et alii, Frattura ed Integrità Strutturale, 34 (2015) 237-245; DOI: 10.3221/IGF-ESIS.34.25 244 brick. The influences of mesh size, propagation criteria, and the choice of the fracture mechanics post-processing tools are studied. Crack propagation simulations are conducted, and the different stages in the crack growth paths are depicted in Fig. 9. The angle of propagation is defined by Eq. (5). Simulations are performed over 16 steps, until the crack reaches the interstitial keyway and reaches the outer boundary of graphite brick. The simulations reveal the non-planar character of propagation and the results clearly demonstrate the capabilities of X-FEM. Ongoing work will be to improve the robustness of 3D non-planar crack propagation in ageing AGR graphite bricks. Step 1 Step 4 Step 8 Step 12 Step16 Figure 9 : Evolution of a non-planar crack path using X-FEM on a full-size graphite brick with stresses coming from UMAT analysis. C ONCLUSION n this paper, numerical applications of X-FEM are presented to demonstrate the crack propagation modelling method in Code_Aster and to show the capabilities of solving the challenging problem in computational fracture mechanics in ageing AGR graphite bricks. The results obtained in the benchmark study shows that the crack paths from X-FEM were similar to the experimental ones. The accuracy of the strain energy release rate computation in a heterogeneous material is evaluated using a finite difference approach. The evolution of the planar crack path on an ageing AGR graphite brick and the non-planar crack path on virgin graphite brick reveal the robustness and the consistency of the propagation. Further work to improve the robustness of 3D non-planar crack propagation in AGR graphite bricks is ongoing. This work contributes to the better understanding of crack propagation behaviour in service, and so contributes to the extension of the AGR plants’ lifetimes in the UK by reducing uncertainties. A CKNOWLEDGEMENTS his work was done as part of a TSB collaborative project between EDF Energy R&D UK Centre, EDF Energy Generation, EDF R&D in France and the University of Manchester. The authors gratefully acknowledge EDF Energy Generation for their valuable input data and support. The views expressed in this paper are those of the I T