Engineering Tools

Glue in Nonlinear Analysis

Engineering Tools — Glue in Nonlinear Analysis

Why this page exists

Glue (BGSET / BCTABLE) is the easy way to tie dissimilar meshes together — no coincident nodes, no hand-built MPCs. It behaves the way you expect in a linear static run. In a nonlinear run it does not, and the difference is quiet enough that it is worth understanding before you trust a result.

Glue in SOL 106 is linear

This is the headline. From the Simcenter / NX Nastran QRG 2401 (BGSET, remark 12):

  "Glue definitions model linear glue behavior in solution 106. The
   glue condition does not update in regard to geometry updates,
   nonlinear material changes, or orientation changes. A glue
   definition should only be defined in portions of the structure
   that exhibit linear behavior."

MSC Nastran is consistent with this: SOL 103 through 112 (which includes SOL 106) and standard SOL 200 can only support permanent glue. The richer glue types — touching, step glue, breaking glue — are SOL 400 features.

Practical consequence: a glue patch in SOL 106 is effectively a linear tie evaluated on the original geometry. Put glue only where the structure stays linear; do not glue across a region that is going to rotate, yield, or undergo large strain and expect the glue to follow.

True nonlinear glue: SOL 400 (MSC) / SOL 401-402 (NX)

If the glued region itself has to behave nonlinearly — large rotation, separation, re-contact — you need the modern nonlinear solutions. There the glue and contact conditions are fully nonlinear: they update with displacement, and step glue / breaking glue become available.

The system call: MSC SYSTEM(758)=2

This is the "system call" the title refers to. In MSC SOL 400, if you have permanently glued contact and the model undergoes large rotation or deformation, permanent glue — which is locked to the original geometry — is the wrong constraint. Setting:

  nastran system(758)=2

tells SOL 400 to automatically switch Permanently Glued Contact to Step Glued Contact when large rotation/deformation is present. The MSC QRG notes that IGLUE is flipped negative automatically in this case. Step glue re-evaluates the glue constraint per step, so it tracks the deforming geometry instead of staying pinned to the initial configuration.

Rule of thumb: SOL 400 + permanent glue + large rotation/deformation → add SYSTEM(758)=2. Without it the glue is silently evaluated on the original geometry and your constraint drifts away from the real interface as the model moves.

Other glue system cells worth knowing (NX)

  • SYSTEM(516)=1 — when gluing solid element faces, NX skips the pair if the face-normal dot product is ≥ 0. Setting this overrides that check so the glue condition is created whenever the search distance is satisfied.
  • SYSTEM(491) / SYSTEM(528) — revert to older glue-stiffness calculation methods (surface-to-surface and linear shell glue respectively). Only relevant when matching legacy results.

Bottom line

  • Glue in SOL 106 is linear and pinned to the original geometry — use it only on linearly-behaving regions.
  • For glue that has to follow a nonlinear deformation, use SOL 400 or SOL 401-402.
  • SOL 400 + permanent glue + large rotation → set SYSTEM(758)=2 so it becomes step glue automatically.