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Workshop2 creep-geo

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Workshop2 creep-geo

  1. 1. Workshop 2 Creating Native Geometry: Pipe Creep Model Introduction Creep is the permanent elongation of a component under a static load maintained for a period of time. Most metals and their alloys creep only at elevated temperatures, but several materials such as thermoplastics and rubbers do so at room temperature. Designers estimating the service life and structural integrity of components must account for creep effects in their designs. This model represents the intersection of a pipe with a cylindrical pressure vessel. The system operates at elevated temperature and carries internal pressure. The calculation consists of two steps. In the first step a static analysis is performed, during which the internal pressure is applied. In the second step a transient analysis is carried out to determine the creep behavior of the pressurized vessel and pipe. The geometry of the model is shown in Figure W2–1. A one-quarter symmetry model is used. Figure W2–1. Sketch of the intersecting pipes
  2. 2. Note: The part created in this workshop will be used in subsequent workshops to build the complete model and perform the analysis. It is important that you use the dimensions stated and not deviate from the workshop instructions; otherwise, you may find it difficult to complete the subsequent workshops. Starting ABAQUS/CAE Start a new session of ABAQUS/CAE from the workshops/pipeCreep directory by typing abaqus cae at the operating system prompt, where abaqus is the command used to run ABAQUS on your system. Select Create Model Database from the Start Session dialog box that appears. Defining the model geometry As always, the first step in creating the model is to define its geometry. In this example you will create a three-dimensional, deformable body to model the pipe intersection. You need to decide what system of units to use in your model. The SI system of meters, kilograms, and hours is used here; you can use another system if you prefer. To create a part: 1. From the Module list located under the toolbar, select Part to enter the Part module. 2. From the main menu bar, select PartCreate to create a new part. Name the part pipe-intersection and accept the default settings of a three- dimensional, deformable body and a solid, extruded base feature in the Create Part dialog box. In the Approximate size text field, type 2. This value is approximately 5 times the outer diameter of the vessel. Click Continue to exit the Create Part dialog box. W2.2
  3. 3. 3. Open the Sketcher Options dialog box by clicking on the customization tool from the Sketcher toolbox. Change the Grid spacing to 0.02 and Decimal places (for sketch dimensions) to 3. Click OK to close the dialog box and to apply the changes. 4. Use the Create Circle: Center and Perimeter tool to sketch two concentric circles of radii 0.24 m and 0.14 m, respectively, centered at the origin. For convenience, align the perimeter points along the X-axis of the sketch plane, as shown in Figure W2–2. 5. Use the Create Dimension: Radial tool to dimension the values of the radii as shown in Figure W2–2. Figure W2–2. Concentric circles 6. Select the Edit Dimension Value tool from the toolbox. Click on the 0.240 dimension in the viewport, and enter a new value of 0.228 m in the prompt area. Click mouse button 2 to modify the dimension. (Mouse button 2 is the middle mouse button on a 3-button mouse; on a 2-button mouse, press both mouse buttons simultaneously.) Similarly, modify the radius of the inner circle to 0.139 m as shown in Figure W2–3. Perimeter points W2.3
  4. 4. Figure W2–3. Modified dimensions of the circles 7. In the prompt area, click Done to continue. 8. The Edit Base Extrusion dialog box appears. Enter a value of 0.458 m for the depth of the solid extrusion and click OK. 9. In the toolbar, click the Render Model: Shaded tool to change the render style to shaded, as shown in Figure W2–4. Figure W2–4. Shaded render style The cross-section of the intersecting pipe must be sketched on a planar region and then extruded. Since the outer surface of the vessel is cylindrical, a datum plane will be created and used for the purpose of sketching the intersecting pipe. 10. From the main menu bar, select ToolsDatum. 11. In the Create Datum dialog box, choose Plane as the type and Offset from principal plane as the method. 12. Click OK. 13. In the prompt area, choose the XZ Plane as the plane from which to offset. W2.4
  5. 5. 14. Specify an offset distance of 0.528 m. Click the Auto-Fit View tool in the toolbar to resize the view. The datum plane is shown in Figure W2–5. 15. From the main menu bar, select ToolsDatum. 16. In the Create Datum dialog box, choose Axis as the type and Principal Axis as the method. 17. Click OK. 18. Create a principal X-Axis as shown in Figure W2–5. Figure W2–5. Datum geometry 19. From the main menu bar, select ShapeSolidExtrude. Do the following: A. In the viewport, select the datum plane as the plane on which to create the sketch. B. Select the datum axis as the edge that will appear vertical and on the right of the sketch. Datum plane Datum axis W2.5
  6. 6. Figure W2–6. Solid extrusion: sketch plane and axis C. Sketch a circle of radius 0.08 m centered in the plane. Place the perimeter point of the circle on the negative horizontal axis of the sketch plane. The reason for this is that the model will later be quartered such that only the upper-right quadrant of the part will be retained. By placing the perimeter point outside of this quadrant, we ensure that no redundant edges will persist afterwards. Dimension the radius of the circle, and modify the dimension to be 0.084 m. D. Click mouse button 2 to continue, and click Done in the prompt area. E. In the Edit Extrusion dialog box, choose the end condition Blind and extrude the solid a depth of 0.35 m. Flip the extrusion direction so that it is pointing toward the vessel, as shown in Figure W2–7. Click OK. W2.6
  7. 7. Figure W2–7. Arrow direction for solid extrusion 20. From the main menu bar, select ShapeCutExtrude. Do the following: A. Select the end plane on the smaller pipe as the plane on which to sketch, as shown in Figure W2–8. F. Select the datum axis as the edge that will appear vertical and on the right. G. Sketch a circle of radius 0.04 m concentric with the circle representing the pipe. As before, place the perimeter point of the circle on the negative horizontal axis of the sketch plane. Dimension the radius of the circle, and modify the dimension to be 0.05 m. H. Click mouse button 2 to continue, and click Done in the prompt area. I. In the Edit Cut Extrusion dialog box, choose the end condition Blind and extrude the cut a depth of 0.528 m. The direction of extrusion is into the pipe, as shown in Figure W2–8. Click OK. W2.7
  8. 8. Figure W2–8. Solid cut 21. From the main menu bar, select ShapeBlendRound/Fillet. Select the edge around the intersection as the edge to be rounded, as shown in Figure W2–9. Specify a fillet radius of 0.04 m. Figure W2–9. Rounded edge 22. Quarter the model as follows: A. From the main menu bar, select ShapeCutExtrude. J. Select the end face of the smaller pipe as the plane on which to sketch. K. Select the datum axis as the edge that will appear vertical and on the right. L. Using the Create Lines: Connected tool located in the upper right-hand corner of the Sketcher toolbox, sketch the series of connected lines shown in Figure W2–10. W2.8 Sketch plane Direction of extrusion Edge that will appear vertical and on the right Edge to be rounded
  9. 9. M. In the Edit Cut Extrusion dialog box, choose the Through All end condition and the direction of extrusion into the pipe. Click OK. Figure W2–10. Cut profile The quarter symmetry model of the pipe intersection is shown in Figure W2–11. Figure W2–11. Final geometry 23. From the main menu bar, select FileSave to save your model in a model database file. You will continue building this model in subsequent workshops. W2.9 Because of how the perimeter points were placed, the edge of the fillet will be removed with this cut. This will facilitate structured meshing in a later workshop.

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