A common practice in Computer-Aided Engineering today is to
A common practice in Computer-Aided Engineering today is to
Purpose– Perform 3D stress analysis– Pipeline a solid model from a CAD software to ANSYS– Determine the mechanical stress in a rotating structure.A common practice in Computer-Aided Engineering today is to utilize Computer Aided Design(CAD) software to do design and export the design to a finite element program to do analysis. Inthis lab, you will create a flywheel model in Creo and conduct stress analysis in ANSYS. Themodel is shown in the Figure below. The flywheel is designed to operate at speeds up to 1000rpm. You will determine whether the spin-induced stress exceeds the yield limit.Because of symmetry, you may consider only 1/12 of the wheel, that is, cut it in half in thethickness direction and take a 60o slice. The dimensions of the reduced model are shown inFigure 2 (unit: in).Figure 1. Flywheel and the solid modelFigure 2. GeometryCreate this model in Creo, export the model to an iges file. Export is as a solid. Later, you willimport this file to ANSYS.Define material propertiesThe flywheel is made of cast iron with the following propertiesYoung’s modulus = 30 ×106 psiYield stress = 22 ×103 psiPoisson’s ratio = 0.30Weight ratio = 0.256 lb/ in3.To analyze spin-induced stress, one must enter the density because the deformation is caused bythe centrifugal force, which depends linearly on the density. Note that for the density input youneed to covert the given weight ratio to a mass density.• Preprocessor > Material Props > Material Model > Structural > Density >Define elementUse “Brick 8node 185” for this analysis. This is the 8-node, tri-linear element which include as adegenerated case the 4-node tetrahedral element.Modeling stepsImport the solid model from the iges file you created:Ansys Utility > File> Import> IGES> > Browse ….Make sure that all other default settings are checked. By checking “Yes” to one of the defaultoptions (“Solid Create solid if applicable”), we require ANSYS to automatically create a solidmodel (i.e., volumes). It is always a good practice to verify whether volumes are indeed defined.If not, you will have to define them in ANSYS.Ansys Utility > List VolumesIf the model is created properly and imported correctly, you should see messages similar to thisNO.SHEL AREAS VOLU #NODES #ELEM MAT REAL TYP ESYS SECN1 1 16 17 18 19 N/A 7245 55788 -1 -1 -1 0 -120 21 22 23Most CAD models contain redundant entities. For example, when two adjacent polygons sharean edge, there are two lines on the common edge, each belonging to one polygon. In ANSYS(and other FEM programs), redundant entities should be eliminated for ease of meshing. This canbe achieved by the “merge” function:Main Menu>Preprocessor>Numbering Ctrls>Merge Items>Type of item to be merge [All] >OK.This will retain a clean solid model for later use.Meshing and boundary conditionsBecause the geometry is irregular, the best way to generate a mesh is to use free mesh. This willgenerate a mesh that contains primarily 4-node tetrahedral elements.For free meshing, as a general strategy, always try to use global size control to specify theelement size. If this option doesn’t produce a desirable mesh, exercise other options.Preprocessor > Meshing > Mesh tool > Size Controls > Global > setThe recommended element size is 0.25 in. Feel free to try different sizes.Preprocessor > Meshing > Mesh tool > mesh [Volume] >Check “Shape Tet” and “Free”.
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