Issue34

T.-T.-G. Vo et alii, Frattura ed Integrità Strutturale, 34 (2015) 237-245; DOI: 10.3221/IGF-ESIS.34.25 243 A parametric analysis has also been conducted using X-FEM in Code_Aster on a full-size brick with initial stresses representing post stress-reversal state of an AGR graphite brick when there are tensile stresses at the keyway corners. The influences of initial crack shape, propagation criteria, and the choice of the fracture mechanics post-processing tools are studied. A first comparison with an ABAQUS model gives good agreement between both codes. Particularly, the evolution of the strain energy release rate with crack propagation is similar (see Fig. 6). Additionally, a good agreement between the local approach and the global approach is seen in Fig. 7. 0 2 4 6 8 10 12 14 16 0 0.01 0.02 0.03 0.04 0.05 0.06 Em ergy release (J) Crack area (m 2 ) Code_Aster ABAQUS Figure 7 : Evolution of the strain energy release rate with crack propagation obtained by Code_Aster and ABAQUS. Fig. 8 shows the full-size brick and the evolution of a crack path under planar propagation. Simulations are performed for 94 steps. The study stopped when the crack propagated fully along the brick height. All crack propagations steps were automatically performed in Code_Aster. It took 7 hours to perform the entire study. Step 2 Step 60 Step 94 Figure 8 : Photograph of a fuel brick (a) and evolution of a planar crack path using X-FEM on a full-size graphite brick with stresses coming from UMAT analysis (b) . Non- planar crack propagation in virgin graphite brick The non-planar crack propagation model is also conducted by using X-FEM. An initial elliptic crack, representing a large, postulated, initial defect, is introduced with initial stresses representing the post stress-reversal state of an AGR graphite a) b)