Boundary Condition Review Checklist
Review prompts for boundary conditions — physical restraint representation, over-constraint, under-constraint, symmetry and rigid-body modes.
Purpose
For checking boundary conditions before accepting FE results for engineering use.
Physical Representation
- Does each constraint represent a physical restraint in the real structure? — A bolted joint is not a fully fixed surface
- Is the support stiffness realistic — not rigid where the support is flexible? — A bracket on a thin panel is not on a rigid wall
- Are bolted or riveted interfaces modelled with appropriate flexibility? — Use connector elements or bolt models, not encastre
- Are bearing supports modelled with appropriate contact or spring behaviour? — Not as fully fixed nodes
Over-Constraint
- Are only the physically restrained DOF constrained? — A pin fixes translations, not rotations
- Is no surface fully fixed unless it is truly clamped to a rigid foundation? — Over-constraint gives artificial stiffness
- Are distributed couplings (RBE3) used rather than rigid links (RBE2) where the support is flexible? — RBE2 over-stiffens
- Is there no stress singularity at a fixed boundary being reported as design stress? — Check stress one or two elements away
Under-Constraint
- Are there enough constraints to prevent rigid-body motion (6 DOF in 3D)? — Check for zero-frequency modes
- If soft springs are used for stabilisation, is their stiffness < 1% of structural stiffness? — And confirmed negligible in results
- In modal analysis, are rigid-body modes at approximately 0 Hz for a free-free model? — Non-zero indicates residual stiffness
Symmetry
- If symmetry is used, are both geometry and every load case symmetric about the plane? — Check each load case independently
- Are symmetry DOF correct for the symmetry plane (not anti-symmetry)? — UY, RX, RZ for XZ symmetry plane
- For mixed symmetric/anti-symmetric loading, are two half-model analyses superposed? — Single run is wrong for mixed loading