NFX contact analysis enforces non-penetration and optional tangential behavior between bodies. The manual covers general contact, rough contact, welded contact, sliding contact, breaking-weld contact, node-to-surface, surface-to-surface, single-surface, and mortar contact.
Contact Search and Discretization
The source distinguishes global contact search from local projection. Contact can be detected through slave node to master segment projection, surface-to-surface integration, or mortar segment integration. It notes the usual tradeoff: node-to-surface contact is cheaper, while surface-to-surface contact is generally more accurate for contact pressure distribution.
Penalty Enforcement
Normal contact force is enforced with a penalty relation based on the normal gap, with contact active when the gap becomes negative. NFX automatically computes penalty stiffness from element/material scale quantities and smooths the contact-force transition to reduce oscillation near contact onset.
Friction and Breaking Weld
Tangential behavior uses a penalty relation coupled to normal contact force. The manual gives a friction yield-like condition based on tangential force norm and mu f_C. Breaking-weld contact maintains welded relative motion until combined normal and tangential contact force measures exceed a failure envelope.
Solver Development Use
For a custom solver, this page separates contact into five testable pieces: search/projection, active set detection, normal penalty force, tangential/friction update, and tangent contribution. Each needs reference-model checks because contact errors can look like element or nonlinear-solver failures.
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