2D meshing

AIM

Carry out the geometry cleanup operation on the given 3 files.

• Practice
• Clip Repair
• Mounting Bracket

OBJECTIVE

We need to mesh the given components.These given parts are sheet metal parts and so that thickness is very low. So instead of going for 3D meshing, We can go for 2D meshing. For that we need to extract the mid surface.Then we need to carry out meshing

WHY we carry out meshing?

The answer is because the original component is having infinite number of atoms in it and when we apply any force the displacement or strain is happened to each and every atom inside it. but infinite number of displacements to find out is impossible. So we need to make the calculation finite. for that we divide the component into a finite number of elements having finite number of nodes. Most useful and popular 2d elements are quad and trias. Trias are being stiffer compared to quads they completely transfer the force applied on it without taking into account the deformation happened to material .So they are to be needed to minimize in the meshing process. Each element is having lines at the outer boundary which is based on the specific shape function of the element. We can find out the values of stress and strain at the nodes of the elements. Since we know the shape function of the element we can find out the displacement and stress values at the particular x and y as we need using the shape function.

For QUAD4 element shape function is u = a₀ + a₁x+a₂y+a₃xy.

FEA will calculates the values at nodes ,ie = a₀,a₁,a₂,a₃ Value of the variable in between nodes can easily be find out using the above shape function.

First step in 2D meshing is to open the hyper works software and in the interface it will ask for to select a solver, Here we select Radioss as solver .Then we need to import the IGES file which is the CAD file of

the part we need to mesh.For that select IMPORT file icon > Then choose the .iges from the directory > Then click on import. Then the Model geometry will be appeared in the screen. This file is the Cad model so the file imported may not be proper and some surfaces may get distorted in the process of importing. So we need to do the clean up the geometry. Some free surfaces may be presented in the imported model, some surface duplication may be seen, some glitches in the surface etc… will be presented. For to remove all these issues before the process of meshing we need to do the topology clean up. We can use visualization option to see the free edges and surface duplications. For that uncheck the green lines which is of shared edges in visualization option and then switch the model into the wireframe mode. Then we can see the duplication of surfaces and free edges. If there is free edges in the geometry expect at holes and outer boundary, Then that is the indication of missing surfaces and improper connectivity. And if there is no T connection and still there are yellow lines present ,Then it is the indication that thee are duplication of surfaces. So we need to delete the duplicate surfaces and for removing the free edges which are red lines ,if present we can use EQUIVALANCE option in edge edit ,TOGGLE option in quick edit can also be used, If these two cant solve the problem we can make use of spline and ruled surface options in SURFACE panel. Also, we can use the replace point option in quick edit tab.Here we can fill the circular holes having diameter less than 5 mm.For that Go to quick edit>fillsurf>click on the circlular line representing hole boundary.

Fig 1 Free edges in Part Fig 2 after geometry clean up

Fig 3 Holes below 5 mm Fig 4 After they are filled

After the geometry cleanup we need to take the mid surface of the model. Since this is having Third dimension which is very very less magnitude. We can take the midsurface and mesh it in 2D and then we can add thickness to the mesh which is exactly same as the model.TO take the midsurface, Go to GEOMETRY tab click on MIDSURFACE, then select the surface for which we need to take the midsurface. Then place the radio button in extraction option and select OFFSEt+SWEPS+PLANES.Then choose auto extraction and click on CREATE. Then we can see the midsurfaces of the component is saved in the new connector. Similarly take the midsurface of each component.

Fig 5 Midsurface of the part

Fig 6 Midsurface of the clip repair

Fig 7 Midsurface of the mounting Bracket

Then we need to do the geometry check or clean up .In that process we need to pay attention of our target element size, minimum element size and maximum element size. We need to defeature the fillets which having possibility of elements failing for minimum size. Ask to CAD Design engineers for the importance of those fillets. If those fillets are not that important then it is permitted to defeature those fillets. For defeature go to geometry tab > defeature> surface fillets> select te fillets we need to defeature>remove. If fillets are between 0.1 mm to 5 mm radius, Then we can remove those fillets.

Cad engineers cannot provide the model in exactly same way as needed in meshing, because the design engineers design the components for purchase engineers and manufacturing engineers. So he kept in mind only the manufacturing perspective while designing. So CAE engineers should remodify the model as per our need.

Then we can start meshing the midsurface. there we can use auto mesh option in 2d panel to mesh the surface.

Go to 2D PANEL> AUTOMESH>Select the surfaces needed to mesh>give the element size AS 5 MM > HIT MESH

Then the whole surfaces got meshed. with the radio button in density we can clean change the nodal densities at various locations so as to get a smooth mesh with lower number of trias. Before accepting the mesh we should change the densities in such a way that the maximum tria removal is possible. Then accept the mesh. Various things to keep in mind in meshing

• If there are any opposite trias ,we should re-mesh these trias and thereby we can remove those trias.
• There should not be any mesh transition at the fillet regions.
• Smoothing command can be used to smoothen the mesh. For that go to TOOL panel >click on SMOOTH> Select the elements needed to smooth>Click on smooth until we get even mesh flow.
• Never place TRIA elements at the edges or inside the washer.
• Adjacent TRIAS must be removed. For that we can use DRAG TRIA option in QUALITY INDEX tab in 2D panel. We can select the tria and drag it to any other position so that we can remove the adjacent trias.
• Rotating Quads are not acceptable in CRASH TEST but acceptable in structural analysis. Same directional following TRIA elements are acceptable in CRASH ANALYSIS but not permissible in structural analysis.
• Always mesh the component keeping in mind the quality requirements.

Fig 8 Trias at the boundary

These type of tria at the boundary condition is not favourable because the tria are stiffer and so they doesn\'t consider the material deformation instead they pass the full amount of force to nearby elemenets.That creats a stress concentration at those regions.That is undesirable.So we need to Drag those trias inside with the quality requiremenets in check.

Fig 9 After the trias are drag back inside

After meshing some of the elements violates the quality criteria . This can be checked by Press F10 which is the check element tab. This can also be entered with Tool>check elements>type the quality in relevant boxes. Then click on the respective options to check whether the elements fail or not. So we should make them follow the quality criteria .For that the tools used are:

1)replace node option. For that PRESS F3 the replace the nodes with each other .

2)Go to QUALITY INDEX then use ELEMENT OPTIMISE ,this is used to optimize the elements based on the criteria we typed in the criteria file settings in the preferences option in menu bar. Go to PREFERANCES> criteria file setting> edit the Table as the quality criteria> then use element optimize and click on near the element we need to optimize.

Yellow color elements means the element is failed. But the red colour element means the element is worst. Touching near the failed element with element optimize will optimize the element.

3)Also we can use place node option in clean up tools in quality index. We can move the node along the surface /Normal to surface to optimize the element.

4)Also smooth tool in TOOL panel also can be used .

5)in case if element need to split ,Then we can make of split element feauture.For that press F6 place the radio button in split and select the elements we need to split, then click the points through which we need to split the elements. Then click split. Then the elements will get split.

6) PRESS F5 which is the mask option so we can save the elements from check elements tab and then we can retrieve those elements using mask option, And we can work on those failed elements without disturbing the other quality elements.

Go to TOOL panel>FIND >choose FIND EDGES.This will ensure there are no free edges in between elements.

Fig 10 Free edge check in part 1 Fig 11 free edge check in Clip repair Fig 12 Free edges check in Mounting Bracket

RESULTS

After Meshing

Fig 13 Part 1 meshed Fig 14 Clip repair meshed Fig 15 Mounting Bracket meshed

After assigning Thickness

Fig 15 Thickness apllied part 1 mesh

Fig 16 Thickness applied on Clip Repair mesh

Fig 17 Thickness apllied Mounting Bracket mesh

Link for the files

https://drive.google.com/drive/folders/1ydfVW-qiH5hxdVg8AQ0xuik4zOxG-tBE?usp=sharing