1. Finite Element Analysis Systems Analysis February 2017
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2. Agenda . Assembly FEM Connections Bolted Connections Modeling Welds
Contact and Glue

3. Assembly FEM
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4. Assembly FEM workflows
Assembly FEMs support two basic workflows:
Associative. In this workflow, you associate an assembly FEM with an existing assembly of parts, and map new or existing component FEMs to each component part.
Non-associative. In this workflow, you first create an empty assembly FEM. You then add component FEMs to the assembly FEM. Finally, you define the position and orientation of component FEMs.

5. Assembly FEM workflows
Associative workflow
Non-associative workflow
1. Create or obtain component FEMs.
2. Create an assembly FEM.
2. Create an empty assembly FEM.
3. Map CAD components to FEMs.
3. Add component FEMs.
4. Define component position and orientation.
4. Connect component FEMs.
5. Connect component FEMs.
5. Resolve label conflicts.
6. Resolve label conflicts.
6. Create a Simulation file.
7. Create a Simulation file.

6. Associative Assembly FEM
An assembly FEM uses the assembly constraints and locations created by the designer. Each component references a component FEM.

7. Creating Associative Assembly FEMs
To create an associative assembly FEM:
Right-click the assembly part node in the Simulation Navigator, and choose New Assembly FEM.
Check the Map to part check box
Select the assembly part.

8. Creating Associated Assembly FEMs
To map existing FEMs to CAD components:
Display the assembly components in the Simulation Navigator
Highlight the CAD component part
Right click and choose Map existing
The FEM will be displayed if loaded, or the user can browse to find the desired FEM file.

9. Non-associative assembly FEMs
Create a non-associative assembly FEM when:
There is no corresponding CAD assembly.
You need to assemble imported, non- geometry-based, or manual meshes.
To add component FEMs to a non-associative assembly FEM, right-click the assembly FEM in the Simulation Navigator and choose Add existing.
If necessary, reposition the component FEMs.

10. Creating non-associative assembly FEMs
Highlight the AFEM in the simulation navigator.
RMB select Add Component
On the form the component can be moved to the desired location.

11. Creating non-associative assembly FEMs
To move the compoment, define the point for the location of the origin. The move component form will display, multiple moves are allowed.

12. Creating non-associative assembly FEMs
The component may be moved after it is added to the AFEM.

13. Using Boundary Conditions from Component SIM
You can include the glue and contact from component FEMs.
Any loads, constraints or simulation objects can be included.
It is usually a good idea to shorten the string for prepending.

14. Using Boundary Conditions from Component SIM
To move the LBCs to the Assembly SIM:
Make the ASIM the displayed part
Open the AFEM and highlight the component part
Under RMB, select Import SIM Entities

15. Assembly Label Manager
The assembly label manager controls the node, element and coordinate system labeling within the AFEM.
When creating a FEM the node and element labels typically start at 1
Combining multiple FEMs will cause conflicts with numbering

16. Load Options
Using the Load Options can reduce the duplicated data and time spent looking for data.
As Saved
Looks in the folders where files were located on last save
From Folder
Looks in current folder - Default
From Search Folders
Looks in folders added to search folders

17. Activity
Assembly FEM
Use assembly FEMs to analyze a large assembly
Use imported mesh data to create an assembly FEM (recommended)

18. Connections
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19. Modeling Options
When multiple bodies or components exist in a FEA model they must be connected to transfer loads and displacements. NX and NX Nastran provide many tools to model connections. The decision on which tool to use depends on the model requirements and the project needs.

20. Connecting Assembly Components
If the components are all modeled with one element type, the connection model selection is more direct.
If the there is a mix of element types especially if they elements have different DOF, the connection selection becomes more difficult.

21. Connecting Component FEMs
If the FEMs brought into the AFEM have coincident nodes, the nodes can be merged at the assembly FEM level without modifying the individual FEMs.
The user may check the entire model by default or select the nodes to be checked.
It is recommended that the user verify the duplicate nodes before merging them.

22. Connecting Component FEMs
In the assembly FEM file, you can define connection elements to join component FEMs into a system using the following tools:
Use the 1 D Connection command to define 1 D connection meshes, spider elements, or connecting structures such as pins, bolts, or struts.
Use manual node and element operations to create individual elements, including lumped mass, shells, or solid elements.

23. Activity
Connecting meshes
Connect nodes with a spider elements

24. Bolted Connections
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25. Connections Representing Bolts
Merge Nodes
No Bolt Stiffness or Forces
Rigid Connection
Additional stiffness
Constraint Element
Flexible connection
Spring Element
Stiffness hand calculated
Beam Element
Closest to bolt, requires elements connecting it to model elements

26. Representing a Bolt with beam and connectors
Bolt Connection
Representing a Bolt with beam and connectors
Result is a recipe that can be edited and updated
Note:- Options will vary according to the Solver environment selected

27. Bolt Connection
Head and Nut diameter to look for nodes to connect with the Spider
Circular Edges Smart Selection to locate hole edges

28. Activity
Bolt modeling and preloads
Model bolted connections

29. Modeling Welds
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30. Weld Assistant
The Weld Assistant is an application available in the Modeling application to create different weld types. The software creates 3D geometry but does not join the bodies.

31. The two bodies do not have to intersect.
Fillet Weld
The two bodies do not have to intersect.
If the bodies do not intersect the user must specify an edge extend.
The shape of the weld is can be convex, concave or straight.
It is recommended that the welds created by CAE users be included in the Idealized part.

32. Mesh Mating can be used in the FEM.
Connecting Meshes
Mesh Mating can be used in the FEM.
The weld mesh and the body mesh will share nodes.
Mesh Mating may be created automatically or manually.
Glue can be used in the SIM.
It can be created automatically or manually.
A stress discontinuity may exist where the .meshes meet

33. Meshing Geometry
It is recommended that the weld be meshed with a reasonable size. The connected bodies be meshed with a global size.

34. CFAST/CWELD Pattern of Points
Replicate spot weld or fastener point patterns in the manufacturing process in the CAE model
The Point on Curve/Edge method that allows pattern input along the curve/edge
Specify distances between points; pattern is repeated along length of curve/edge

35. Number of elements in the weld layer Element size along the weld edge
Weld Rows
Improves process to generate 2D element weld rows on welded plate models
Provides a mesh density based upon edges and related faces that have welds applied to them
Required Input:
Size of weld layer
Number of elements in the weld layer
Element size along the weld edge
Generate weld mesh first
Fill remainder of faces with 2D elements
Store both as separate meshes
Tracked together
May be assigned to different collectors

36. Advanced Simulation examples Shell meshing a welded structure
Activity
Advanced Simulation examples
Shell meshing a welded structure

37. Contact and Glue
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38. Connecting Component FEMs
In the Simulation file, you can use the Surface-to-Surface Contact command and the Surface-to-Surface Gluing command to constrain behavior at adjacent faces of component FEMs.

39. If u(t) < d then u = u If u(t)  d then u = d What is Contact?
Contact detects and prevents penetration between two bodies.
Surfaces are touching
(penetration distance is zero)
Surfaces are not touching
(traction force is zero)
If u(t) < d then u = u
If u(t)  d then u = d
Where:
u is the current displacement
d is the gap or contact distance

40. Linear Contact
Valid for small displacement theory, supports friction
Used in Linear static solution, SOL 101
Can be used as a preload in SOL 103
Surface to surface for all solid and shell element types
Gap elements may be included

41. Advantages of the augmented Lagrangian method :
Contact Solution
Advantages of the augmented Lagrangian method :
The contact constraints may be achieved to almost any accuracy using a series of contact traction updates.
A lower penalty number can be used resulting in better conditioned equations.
Contacting bodies can be restrained using only contact constraints.
Linear contact can be used only in NX Nastran Linear Statics solutions.
Glued contact can be used in ALL NX Nastran solutions.

42. Mesh Considerations
The mesh must be able to represent the contact area.
Identical surface meshes are not required.
Element types do not have to match.

43. Using Contact
For each body all degrees of freedom except the direction of contact must be restrained.
For stability a spring element can be used.
Contact can remove rigid body motions from the structure.
Shell Elements
The thickness is taken into account by default
Set the correct side for contact
Adding friction will help improve model stability.

44. How to Define Contact
Contact pairs may be created automatically from polygon geometry.
The user may manually select pairs from geometry or groups of element faces.

45. Defining Pairs for Contact
Friction
The Coulomb friction coefficient is multiplied by the normal force to determine when sliding occurs
Search Distance
The minimum and maximum search distance defines a range in which the solver can create contact elements.
These values are used only once.
There are no geometric nonlinear updates.

46. Contact Pair Parameters
Minimum Distance
Use a small distance if parabolic elements are used. This will prevent penetration.
Can be negative if there is an interference fit condition
Maximum Distance
A large value can be used to make sure that all contact elements are created
It should be reasonable. Excessively large values used with the global search can cause solution failures.

47. Defining surface-to-surface gluing
Create a Surface-to-Surface Gluing simulation object to connect two surfaces to prevent relative motion in all directions.
The automatic pairing works the same as for contact.
A region is a collection of element free faces which will be glued together.
These regions can be created using shell elements and using free faces of solid elements.

48. Defining edge-to-surface gluing
Use the Edge-to-Surface Gluing simulation object to connect an edge to a surface to prevent relative motion in all directions. An NX Nastran glue connection is a simple and effective method to join dissimilar meshes. The glue connection correctly transfers displacement and loads, which results in an accurate strain and stress condition at the interface. NX Nastran uses a weld-like formulation to create the connection.
Note
The nodes on the glued edges and surfaces do not need to be coincident.

49. Edge-to-Surface Glue for Modeling
Glue Connection
Mesh stitching not required – simplifies modeling
Thickness effects correctly modeled at joints – more accurate
Glue connection details
Imaginary rigid face created perpendicular to glue edge
Surface-surface contact made between imaginary face and glue face t1
Joint Geometry
Edge-Surface Glue with
Mid-Surface Mesh t2
Imaginary face contact surface t1

50. Define contact conditions for a model
Activity
Contact and gluing
Define contact conditions for a model
Define glue conditions for a model
Glue edges to surfaces

51. Thank you ! E-mail: Marilyn.Tomlin@Siemens.com
Marilyn Tomlin Advanced Application Engineer CAE COE
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