PSI - Issue 28

J. Xue et al. / Procedia Structural Integrity 28 (2020) 1047–1054 and W.R. Tyson/ Structural Integrity Procedia 00 (2019) 000–000

1050 4

J. Xue, B. Williams, S.

Fig. 1. Damage initiation strain as a function of stress triaxility and normalized Lode angle

2.2. Mesh and boundary conditions The DWTT model shown in Fig. 2 was used to investigate the effect of bending and uniaxial tension loading modes. The DWTT specimen is 13.7 mm in thickness; 76 mm in width; 305 mm in length, and the ligament length is 66 mm. The X80 model was calibrated for a mesh size of 0.5 mm along the crack path. A coarse mesh of 2 mm was used for the rest of the model to reduce computational cost. Tie constraint was used for the transition from fine mesh to coarse mesh. A quarter-symmetric model was used to reduce computational cost. For the case of the DWTT three-point bending model, the hammer and supports were modelled as displacement controlled rigid surfaces. Contact constraints were defined between the rigid surfaces and the elements. Friction is not considered in the contact constraints. For the case of the DWTT tension model, one edge of the specimen was loaded in displacement control as a function of time in the X direction to simulate uniaxial tension.

Fig. 2. Boundary conditions of (a) DWTT bending model and (b) DWTT tension model.

3. Results and discussions The MMC model for X80 validated with the Emc2 RR test results was used in the following sections. Instead of the explicit solution used in section 3.1, an implicit solution was used for more stable crack propagation. The MMC model was not capable of capturing slant fracture (with the size of elements considered). However, this further eliminated a source of variability in the simulations because CTOA values were only measured for flat, tunneling fracture as opposed to the more complex flat/slant fracture. Both DWTT bending and tension MMC models show stable crack propagation and predict tunneling fracture. Crack propagation is analyzed numerically by removing the