INSTRUCTIONS FOR USING ABAQUS/CAE IN ANALYZING PIPE WITH A CRACK

(Version 6.6-1)

A. Solid Modeling and Subregions

1. Go to Start> All programs>Engineering Software>ABAQUS 6.6-1>ABAQUS CAE. An ABAQUS/CAE Version 6.6-1 viewport appears.

2. Select Create Model Database in the Start Session window. 3. Double-click the Parts container (same as right-click and select Create) in the model tree.

A Create Part window appears. Accept default features in that window by clicking Continue. A sketcher window with a sketcher toolbox and a grid appears.

4. Click Create Arc: Center and 2 Endpoints from the sketcher toolbox. Type 0,0 to define

the center of the pipe cross-section at the bottom and hit Enter. Type 0,53.34 to define the coordinate of the intersection (top) of the vertical centerline and outer circumference of the pipe cross-section and hit Enter. Type 0,-53.34 to define the coordinate of the intersection (bottom) of the vertical centerline and outer circumference of the pipe cross-section and hit Enter. The outer arc of the quarter pipe appears.

5. Repeat step 4 for the inner circumference by typing 0,0; 0,48.26; and 0,-48.26 to obtain the

inner arc of the quarter pipe. Type Esc to get out. 6. Click Create Lines: Connected from the sketcher toolbox. Join the top two points by

clicking them one by one, and then type Esc. Repeat the same for the bottom two points, and type Esc. Click Done. An Edit Base Extrusion window appears. Type 750 for the depth and click OK. A solid model of the quarter pipe is generated and appears on the screen, as shown in Figure 1.

7. Click Create Datum Plane: Offset From Principal Plane from the Parts toolbox. Click

XY Plane at the bottom. Type an offset value of 450 (origin at the right end) and hit Enter. A datum plane appears. Repeat the same procedure for an offset value of 730, creating another datum plane closer to the cracked cross-section (left end).

8. Expand (click and keep pressing) Partition Cell from the Parts toolbox and select

Partition Cell: Use Datum Plane (2nd from left). Select the right datum plane. Click Create Partition, pick the cell to partition, and select Done, which creates two cells (subregions). Select the left datum plane, again click Create Partition, pick the cell to be partitioned, and click Done, creating a total of three cells (subregions) in the longitudinal direction (Figure 2). Unselect Partition Cell: Use Datum Plane or click Cancel Procedure (X) at bottom to get out (optional).

2

Figure 1

Figure 2

3

9. Zoom the crack-tip region and pick the wireframe view. Expand Partition Edge from the Parts toolbox and select Partition Edge: Select Midpoint/Datum Point. Click on the outer arc of the cracked cross-section and a midpoint of the edge appears. Click on the midpoint and then select Create Partition to divide the outer arc into two. Repeat the process twice until the midpoint of the upper part of the arc coincides with the crack tip.

10. Repeat step 9 for the inner arc of the cracked cross-section and for both the outer and inner

arcs of the datum plane closer to the cracked cross-section. Unselect Partition Edge: Select Midpoint/Datum Point or click Cancel Procedure (X) at bottom to get out.

11. Expand Partition Cell from the Parts toolbox and select Partition Cell: Use N-Sided

Patch (5th from left). Click on the left cell (subregion between the cracked cross-section and the closer datum plane) of the pipe model. Click Select Corner Points and then click 4 for the Number of Corner Points (at bottom). Various control points of all edges of the cell appear. Define 4 corner points in the loop by clicking the outer crack tip (point 1), the outer datum plane point (point 2), the inner datum plane point (point 3) and the inner crack tip (point 4). Click Create Partition, which leads to a division of the cell into two.

12. Repeat step 11 by clicking the outer mesh symmetry point (point 1), the outer datum plane

point (point 2), the inner datum plane point (point 3) and the inner mesh symmetry point (point 4). Click Create Partition, forming another division of the cell into two, as shown in Figure 3.

13. Repeat the process in steps 11 or 12 by dividing each of the upper two (smaller) rectangular

cells into two triangular cells, as shown in Figure 4. 14. Expand Partition Edge from the Parts toolbox and select Partition Edge: Enter

Parameter. Click on the edge that is the outer arc of the top triangular cell and click Done (at bottom). An arrow appears on the edge selected. Based on the direction of the arrow, type 0.95 (if the arrow is directed towards the crack tip) or 0.05 (otherwise) in assigning Normalized Edge Parameter (at bottom). Click Create Partition, which locates a point on the edge for the wedge-shaped elements. Repeat the process for each of the remaining 4 edges emanating from the crack tip.

15. Repeat step 14 for all 5 edges emanating from the crack tip at the inside surface. 16. Expand Partition Cell from the Parts toolbox and select Partition Cell: Use N-Sided

Patch. Repeat step 11 four times to construct the 4 cells for the wedge-shaped elements. Figure 5 shows the resulting solid model of the quarter pipe.

Save the CAE file (e.g., cp4.cae) in your local directory (e.g., c:\temp).

4

Figure 3

Figure 4

5

Figure 5

6

B. Material Property, Instance, Cracks, Steps, Loads, and BCs 17. Import cp4.cae into ABAQUS/CAE. 18. Double-click the Materials container in the model tree. A Edit Material window appears.

Click Mechanical>Deformation Plasticity from the menu in that window. Define Ramberg-Osgood parameters by typing: 207000 (Youngs modulus), 0.3 (Poissons ratio), 344.8 (Yield Stress), 5 (Exponent), and 1 (Yield Offset). Click OK.

19. Double-click the Sections container in the model tree. A Create Section window appears.

Accept default parameters by clicking Continue and OK. 20. Expand the Parts container and then the Part-1 subcontainer in the model tree. Double-

click Section Assignments and define a window with the mouse enclosing the whole model. Click Done at the bottom and then click OK.

21. Expand the Assembly container in the model tree. Double-click Instances subcontainer,

which opens a Create Instance window. Select Independent for the instance type and click OK.

22. Expand the Engineering Features subcontainer of the Assembly container. Double-click

Cracks and a Create Crack window appears. Click Continue. Define the crack front on an enlarged view of the cracked cross-section and click Done. Click q vectors. Click on the outer crack tip as the starting point and on the adjacent node (outer arc) as the end point of the q vector, which opens an Edit Crack window. Select On symmetry plane in the General subwindow and Collapsed element side, duplicate nodes in the Singularity subwindow. Click OK.

23. Double-click the Steps container in the model tree. A Create Step window appears.

Accept default parameters by clicking Continue and an Edit Step Window appears. Select Fixed in the Incrementation subwindow and type 0.1 for Increment size. Click OK.

24. Double-click the Loads subcontainer in the model tree. A Create Load window appears.

Accept default parameters and click Continue. Change orientation to view points on the farthest datum plane from the cracked cross-section. Click on the load point that is located at the outer arc (bottom) of the farthest datum plane and click Done. An Edit Load window appears, in which a value of 31719.5 should be typed for CF2. Click OK.

25. Double-click the BCs subcontainer in the model tree. A Create Boundary Condition

window appears. Select Displacement/Rotation for Types for Selected Step and click Continue. Click on the rear BC point that is located at the outer arc (top) of the end cross-section of the pipe and click Done. An Edit Boundary Condition window appears, in which U2 should be clicked to set it to zero. Click OK.

26. Repeat step 25 two times for enforcing appropriate BCs on z-faces (U3 = 0) and on x-faces

(U1 = 0) that have symmetry. Before doing so, click on Show/Hide Selection Options (at

7

bottom) to pick Faces in the Options window. Changes in the orientation and/or zooming may be required to be able to select the appropriate faces. Figure 6 shows a snapshot of loads and BCs imposed on the pipe model.

Figure 6

8

C. Mesh Generation and Output Option 27. Expand the Instances subcontainer of the Assembly container all the way through.

Double-click Mesh to open a mesh toolbox. Click Seed>Instance and a Global Seeds window appears. Type 10 for Approximate Global Size and click OK. A mesh seeding appears on the screen. Click Done.

28. Zoom the crack-tip region and pick the shaded view. Click Seed>Edge by Number and

click on Show/Hide Selection Options (at bottom) to pick Faces in the Options window. Click top faces of the four trapezoidal (partitioned triangular) cells and click Done. Type 10 for the Number of elements along the edges (at bottom) and hit Enter. Flip the view and repeat the procedure for the bottom faces of the same four trapezoidal cells. Type Esc, several times if needed, to get out.

29. Click Mesh>Controls. Define a window with the mouse enclosing the whole model.

Click Done at the bottom. A Mesh Controls window appears. Select Sweep for Technique and click OK. Select Cells in the Options window, click four triangular cells at crack tip in an enlarged view, and click Done. A Mesh Controls window appears again. Select Wedge for Element Shape and click OK. Click Done.

30. Click Mesh>Element Type. Define a window with the mouse enclosing the whole model.

Click Done at the bottom. An Element Type window appears. Select Quadratic for Geometric Order and unselect Reduced Integration. Click OK. Click Done.

31. Click Mesh>Instance. Click Yes at the bottom. A mesh will be created, as shown in

Figure 7. 32. Double-click the History Output Requests container in the model tree. A Create History

window appears. Click Continue and an Edit History Output Request window appears. Select Contour Integral in Domain and type 8 for Number of contours. Click OK.

33. Save the model created using File>Save As option in the local drive of your computer.

You can perform this operation anytime during preprocessing.

9

Figure 7

10

D. Analysis 34. In the Analysis tree, double-click the Jobs container to create a new job. A Create Job

window appears. Click Continue and OK. 35. Right-click the Job-1 subcontainer and submit the new job created. 36. After the job is completed save the CAE file again. E. Post-processing 37. Right-click on completed job in the Jobs container and select Results to enter the

Visualization module. 38. Click on the Allow Multiple Plot States icon to superimpose undeformed and deformed

geometry and deselect Allow Multiple Plot States after taking appropriate snapshot(s). 39. Click Results>History Output to open a History Output window. Select J-integral for all

three crack tips (1, 2, and 3) and a specific contour (e.g., 8th). Click Plot in the History Output window. Click Save As and OK to obtain the X-Y data. The X-Y data are saved in the XYData container of the Results tree.

40. To save all results, save the associated ODB file in the local directory.