Finite Element Analysis Systems Analysis February 2017 Restricted © Siemens AG 2017 Realize innovation.

Agenda . Assembly FEM Connections Bolted Connections Modeling Welds Contact and Glue

Assembly FEM Restricted © Siemens AG 2017 Realize innovation.

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.

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.

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

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.

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.

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.

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.

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.

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

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.

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

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

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

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

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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.

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.

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.

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.

Activity Connecting meshes Connect nodes with a spider elements

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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

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

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

Activity Bolt modeling and preloads Model bolted connections

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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.

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.

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

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

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

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

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

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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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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