Minidisc Crack Growth Analyses

The ANSYS minidisc model was obtained from WPAF and analyzed using ANSYS to compute the initial uncracked stress state (see Figure 1).

Figure 1. Uncracked minidisc model – maximum principle stress contours.

A single sector of the model had been meshed with greater refinement than the rest of the sectors. This sector was extracted from the ANSYS model and read into Franc3D/NG. It was decided that this refined initial mesh was still too coarse to perform crack growth analyses; it did not capture the geometry accurately and crack insertion and crack growth were impeded by the coarse mesh that was retained on the boundaries of the sector. We refined this sector in ANSYS, remapped the temperatures, and reran the uncracked analysis. The refined sector is shown in Figure 2.

Figure 2. Uncracked minidisk model – one sector with a refined mesh.

The maximum principle stress contours for the uncracked analysis are shown in Figures 3a and 3b. There are high tensile stresses in a couple of locations. Figures 3 and 4 show the stress contours for the refined-mesh sector.

Figure 3. Uncracked maximum principle stress contours.

Figure 4. Uncracked maximum principle stress contours for refined-mesh sector with initial crack locations.

Based on the analyses previously done by WPAF, based on the stress contours in the uncracked model, and based on the paper by Russ et al (2004), we started three crack growth analyses; the initial crack locations for these analyses are shown in Figure 4. Automatic crack growth analyses have been carried out for all three cracks. The slot-crack has been propagated for 22 steps, the front-bore-crack has been propagated for 25 steps, and the bore-crack has been propagated for 13 steps. (The bore-crack is currently being propagated further after another bug fix in Franc3D/NG.) The initial and current crack shapes are shown in Figures 5a-f.

Figure 5a-b. Franc3D/NG crack shape for initial front-bore crack and for step 25.

Figure 5c-d. Franc3D/NG crack shape for initial bore crack and for step 13.

Figure 5e-f. Crack shape for initial slot crack and for step 22.

Figures 6-8 show the deformed shapes with maximum principle stress contours for the current crack steps for each crack.

Figure 6. Front bore crack – step 25 – deformed shape and maximum principle stress contours.

Figure 7. Bore crack – step 13 – deformed shape and maximum principle stress contours.

Figure 8. Slot crack – step 22 – deformed shape and maximum principle stress contours.

Russ, S. M., Rosenberger, A. H., Larsen, J. M., Berkley, R. B., Carroll, D., Cowles, B. A., Holmes, R. A., Littles, J. W., Jr., Pettit, R. G., and Schirra, J. J., “Demonstration of Advanced Life-prediction and State-awareness Technologies Necessary for Prognosis of Turbine Engine Disks”, Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, Proceedings of SPIE, Vol. 5394, Edited by Tribikram Kundu, SPIE, Bellingham, WA, pp. 23-32, July 2004.

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