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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

Modeling Interactions & Assemblies

Joël Cugnoni, LMAF/EPFL, 2012

advanced boundary conditions interactions
Advanced boundary conditions & interactions
  • 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
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
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
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
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
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
    • add instance for biele1
    • align with coaxial +face2face +4mm offset
    • assign properties to all parts / regions and then create step
    • create 1st constraint: tie for axis to biele surfaces
    • create datum point in the middle of lower biele axis
    • create reference point
    • create constraint: kinematic coupling btw RP and lower axis of biele
    • boundary condition: pressure 0.1MPa on top of cylinder, all displacement & rotation constrained on RP
    • mesh fused part with tets quad 2.8mm
    • mesh biele with hexa sweep or wedges (partition by extending faces)
    • run job
    • show results with several cutting plane to show
      • 1) mesh continuity between the merged parts
      • 2) displacement continuity but mesh discontinuity where tie is used