Importing Parts/Assemblies Parts/Assemblies Into Abaqus/CAE INTRODUCTION Abaqus/CAE can import part and assembly geometries from a variety of external sources and third-party CAD systems. You can directly import parts from specific programs that Abaqus/CAE is programmed to recognize which are listed on their website. If possible you will want to import parts in their native file format from the CAD program used to create them. Both CATIA and AUTOCAD are recognized by Abaqus/CAE. Solidworks files should be saved as Parasolid files. Sometimes it is more convenient to import parts that are saved in a standardized neutral file format such as IGES or STEP files.
Many of the problems associated with importing a complex solid part into Abaqus/CAE can be alleviated if you recognize what you want as an end product: a finite element mesh of the parts to be analyzed using Abaqus/Standard or Abaqus/Explicit. Abaqus/Explicit . A small feature in the imported part will result in a fine mesh in the area of the detail. The fine mesh will influence the mesh in adjacent regions and may dominate the time taken to perform the analysis. If you are not interested in analyzing the feature, you should use the CAD system to remove the detail from the part before you import the part into Abaqus/CAE. Removing small features may solve precision errors in the imported part. Examples of small features include: Fillets Chamfers Holes Simplifying a solid part will increase your your chances of successfully importing it into Abaqus/CAE. You must decide the level of detail that will produce meaningful results from the analysis. Finally, you should consider the type of mesh required by the analysis. If you plan to mesh the part with triangular or tetrahedral elements or with quadrilateral elements generated by the advancing front algorithm, you can use the Virtual Topology toolset in the Mesh module to remove small details from the part before you generate the mesh.
In this example we will show how to import a part saved as a STEP file and what happens when you have details that are not necessary for your analysis. The part we will be working on is shown below in Figure 1.
Figure 1: Connecting Lug Example CREATING A PART It is assumed at this point that you know how to create a part in Abaqus/CAE and in Solidworks or any similar CAD program. Please make the part shown above in Abaqus/CAE and any third party CAD program that can save a .step file. When saving the part as a .step file in Solidworks, either AP203 or AP214 will work. Also, Solidworks will save the .step file as a .STEP file. Abaqus/CAE will not recognize the capitalization of the .step file and you must rename the file extension to be all lowercase. Also make the exact same part but with a .002m radius fillet.
IMPORTING THE PART Select FileImportPart from the main menu bar to import a part from a STEP-format file. You can export sketches and parts from Abaqus/CAE into a STEP-format file, but you cannot export the assembly to a STEPformat file. To import a part from a STEP-format file: 1. From the main menu bar, select File Import Part. The Import Part dialog box appears. 2. From the File Filter menu at the bottom of the Import Part dialog box, select STEP (*.stp, *.step). Abaqus/CAE lists all the files in the selected directory with a .stp or .step file extension. 3. Select the STEP file containing the part to import, and click OK. Abaqus/CAE displays the Create Part from STEP File dialog box. 4. Click the Name-Repair tab to set the following: a. Name: The name of the new part. b. Topology: Abaqus/CAE selects the topology — solid, shell, or wire — based on the entities that it finds in the file. In most cases you should accept the setting selected by Abaqus/CAE. However, if the topology of the resulting part is not as expected, you can try importing the part again with a different topology selected. c. Part Filter: A STEP file can contain more than one part, and Abaqus/CAE imports all of the parts in the file by default. If you import all the parts in the STEP file, you can create individual Abaqus parts for each of them or you can combine them together into a single Abaqus part; in addition, if you combine these parts, Abaqus/CAE enables you to stitch these imported parts together using a user-specified stitching tolerance value. If you want to import an individual part from the STEP file, you can toggle on Import part number and enter the number of a single part to import from the file. 5. Click the Part Attributes tab to set the following: a. The modeling space of the part being imported. When you import a part, Abaqus/CAE scans the file and tries to determine the modeling space. b. The type of the part being imported. Abaqus/CAE always assumes that the part type is deformable. Alternatively, you can select Discrete rigid to import a discrete rigid part or select Eulerian to import an Eulerian part. c. Again, in most cases you should accept the default settings. 6. Click the Scale tab to scale the part during the import process. a. Choose No scale to maintain the dimensions stored in the file. b. Choose Use transform from file, including scale to read the scale factor, the rotation matrix, and the translation matrix from the STEP file. c. Choose Multiply all lengths by, and enter a scale factor. Abaqus/CAE applies the scale factor to all of the coordinates in the file. As a consequence, any offset from the origin will be scaled accordingly. 7. Click OK to import the STEP part and to close the Create Part from STEP File dialog box. →
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Abaqus/CAE scans the STEP file and starts the repair process, depending on the options selected. If you wish to cancel the import process, click Stop in the prompt area. When you import a single part, Abaqus/CAE displays a message indicating if the part contains any validity or precision problems. If you import multiple parts from a single STEP file, you can use the Part Manager to check if any of the parts are invalid or imprecise. If necessary, use the Query toolset to locate areas of invalid and imprecise geometry. EVALUATING THE IMPORTED PART When importing parts saved as .step files, they are imported as a single part and you can not edit features already made using previous CAD programs. You can make new features using the Abaqus/CAE interface. When comparing the part made in Solidworks to the part made in Abaqus/CAE we can see that they are identical. This is the most ideal situation and usually occurs when the part made in Solidworks or any other CAD program does not have any complex features. You can see, from the color of the imported part, in the Mesh module that the lug with no fillets is already meshable using a sweep method and hex elements. This is shown in Figure 2.
Figure 2: Sweep mesh indication on Lug If we wanted to do a structured mesh with hex elements, which would gives us more control over the mesh, we only need to do simple partitioning. The partitioned Lug with structured mesh capability is shown in Figure 3.
Figure 3: Structured mesh capability with partitions If we look at the lug with fillets on it in the mesh module we see that the Lug has an orange color, which indicates that it is un-meshable with hexes and wedges. Figure 4 shows the lug with fillets in the mesh module. Even if you were to partition this part the same way as the lug without fillets, you will still not be able to mesh with hexes and wedges on most of the part. More complex and intricate partitioning will be necessary in order to be able to mesh the part with hexes. It would be easier and less time consuming if the lug did not have fillets at all.
Figure 4: Lug with fillets un-meshable with hexes and wedges To get the lug with fillets to be meshable with hexes and wedges takes 23 steps while getting the lug without fillets to be meshable with hexes and wedges takes 2 steps. This is shown in Figure 5. A comparison of the two meshes can be seen in Figure 6.
Figure 5: Number of features for lug and lug with fillet
Figure 6: Comparison of lug mesh with and without fillets It took 784 elements to mesh the lug without fillet and 2616 elements to mesh the lug with fillets, both with the same seed size. That is a little over 3 times as many elements just on a very simple part with fillets. Sometimes importing parts is not as smooth as it was for this example. For more complex parts there will be errors that you will have to fix either in Abaqus/CAE or in the CAD program used to create the part. An example of this is seen in Figure 7.
Figure 7: Imprecise geometry error with importing
