Modeling Interactions & Assemblies

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# Modeling Interactions & Assemblies - PowerPoint PPT Presentation

Modeling Interactions & Assemblies . Joël Cugnoni, LMAF/EPFL, 2012. Advanced boundary conditions & interactions. How can we model more complex cases ?

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### Modeling Interactions & Assemblies

Joël Cugnoni, LMAF/EPFL, 2012

• How can we model more complex cases ?
• It is possible to define interactions between different regions of a model by the means of additional equations that relate the degrees of freedoms of multiple nodes.
• Bilateral constraints to “glue” separate parts:
• Node to node interaction : Equation constraint
• Node to surface interaction : Kinematic coupling
• Surface to surface interation: Tie constraint
• Unilateral constraints:
• Contact: no penetration between two faces, friction & sliding => non linear behaviour, not in course
Node to node constraint: equation
• Available in Interaction->Constraints->Equation
• one linear equation between several DOFs

a1 Node1.DOF1 + a2 Node2.DOF2 + … = constant

Antisymmetry

Mechanism (Pulley)

1 * Node17.U1 + 1 * Node23.U1 = 0

1 * Node12.U2 - 1 * Node21.U1 = 0

17

23

21

y

14

x

Node to Surface constraint: coupling
• Available in Interaction->Constraints->Coupling->Kinematic coupling
• Multiple equations to keep relative position constant including rotations
• Tranfers the displacements / rotation of the Master node to slave surface
• Usually used with reference points to link parts or apply moments / rotation to one face

Master Node : reference point with 6 DOFS

Kinematic coupling

y

Slave Nodes : 3 DOFS

x

Surface to Surface constraint: Tie
• Available in Interaction->Constraints->Tie
• Multiple kinematic equations to keep relative position constant between each point of the master surface and their corresponding projection on the slave surface
• Usually used to link two parts of an assembly to ensure continuity of the displacements (approximation)

Slave surface

Small distance

(projection tolerance)

Projection lines

Master surface

y

x

Modelling Assemblies
• Three methods:
• Continuous CAD model:Merge all parts in CAD -> export STP model -> import in Abaqus -> partition to differentiate the materials
• Merged geometry: model as an assembly in CAD -> export as STP -> import in Abaqus -> create assembly and position parts -> Merge geometry + keep internal interfaces
• Tie / coupling constraints: model as an assembly in CAD -> export as STP -> import in Abaqus -> create assembly and position parts -> Create Tie / coupling to model the interactions between parts
Demonstration of the concepts
• See assembly1.cae
• Procedure:
• open assembly1-input.cae
• create instance for piston and axe1
• align axe1 with coaxial + face to face (-13mm offset)
• merge and keep interfaces