WORKSHOP 6.3 WELD FATIGUE USING NOMINAL STRESS METHOD. For ANSYS release 14

Transcription

1 WORKSHOP 6.3 WELD FATIGUE USING NOMINAL STRESS METHOD For ANSYS release 14

2 Objective: In this workshop, a weld fatigue analysis on a VKR-beam with a plate on top using the nominal stress method is demonstrated. Goal: The goal is determine the fatigue life due to a varying bending moment using the nominal stress method. Page 2

3 1. Launch ANSYS WorkBench: a. From the Project Page, in the File menu select Restore Archive and click on [Browse] b. Select the Workbench archive Workshop_6_3_geometry.wbpz and click on [Open] c. Save the model in the training directory specified by the teacher. Page 3

4 2. Add a Static Structural analysis connection to existing geometry: 3. Open the Simulation file: The Workbench Project page will appear. Either double-click on the Setup (highlighted) to open the existing Simulation database Static Structural or right click and select Edit. Page 4

5 4. Review the geometry: Note that the beam and plate is two separate bodies. Bonded contact is used to connect the two bodies. See that the bottom surface of the plate has an imprint simulating where the weld is connected to the VKR-beam. 5. Review the contact pair: The default contact setup create bonded contact between top surface of beam and both surfaces on top plate. This is not OK. Delete the contact pair. In the settings of Detail of Contacts change Group by to None. Page 5

6 6. Create the contacts: Right click on Contacts and select create automatic contacts. 7. Review and suppress contact pair Two separate contact pairs have now been created. Suppress the contact pair between the large surface of the plate and top surface of the VKR-beam. The result of this is that the two bodies only are connected through the weld. Another option is to change the contact type to frictionless or frictional contact. Page 6

7 8. Create the mesh: The default settings will generate a relative course mesh. A rule of thumb is trying to keep the ratio between shortest and longest element edge less than 1/3. In some situations the ratio 1/5 may be acceptable. Introduce mesh controls to generate a finer mesh (sizing, relevance, global sizing etc.). 9. Apply displacement boundary conditions In Outline select Static Structural Select the two surfaces in the symmetry cut. Under Supports select Remote Displacement and enter 0 (zero) for all displacement and rotational components. Page 7

8 11. Apply bending moment: Select the surface at free end of the VKR-beam. Under Loads Select Moment Under Details of Moment change Define By to Components and specify a bending moment about the X-axis of Nmm. Page 8

9 12. Define a path for results evaluation: This operation can be made any time, also after the solution is done. Click on Model on top in Outline and select Construction Geometry Having Construction Geometry selected, click on Path Under Details of Path enter 101 for Number of Sampling Points. Page 9

10 13. Define a path for results evaluation, continued: Select and use the line at the weld toe for start point of path. Select and use the line at free end of VKR-beam as end point of path. Page 10

11 14. Create global results plots for: Total deformation Von Mises Stress Maximum Principal 15. Create results on Path: Create an additional results for principal stress. In Details of Principal Stress 2 change scoping method to Path Select Path in drop list Other options available is to scope the results for a specific body or if the non averaged results should be used. 16. Save the project 17. Run the analysis Page 11

12 18. Review the results for: Total deformation (pay attention to local deformation in VKR-beam near weld) Von Mises Stress Maximum Principal (global and path) What is the nominal stress in VKR-beam? Answer: MPa 19. Calculate fatigue life: This joint type have the fatigue weld class FAT=50 according to IIW-1823, Detail category G according to DNV RP-C203 (equal to FAT50) and detail category 56 according to Eurocode 3. Use FAT50 and m=3. m 6 FAT N = 2 10 σ Calculated fatigue life is cycles. Page 12