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Modeling Interactions & Assemblies

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

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  1. Modeling Interactions & Assemblies Joël Cugnoni, LMAF/EPFL, 2012

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

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