curing-contact

# Curing Contact Setup Define the frictional contact between the composite (P8-1) and the mold (TOOL-1). This is the physical mechanism that constrains the composite during curing and creates asymmetric springback upon demolding. ## When to Invoke - User asks to set up contact between composite and mold - User mentions "接触", "摩擦", "模具接触", "contact pair" - User needs to change friction coefficients - User encounters contact-related convergence issues ## Contact Pair Definition ``` *Surface, type=ELEMENT, name=com-surface P8-1.S1 # Composite outer surface (contact with mold) *Surface, type=ELEMENT, name=tool-surface TOOL-1.S4, S6 # Mold contact surfaces *Contact Pair, interaction=INTER-1, type=SURFACE TO SURFACE com-surface, tool-surface # Master: tool, Slave: composite ``` **Surface assignments**: | Surface | Part | Element Face | Role | |---------|------|-------------|------| | `com-surface` | P8-1 (composite) | S1 (outer) | Slave surface | | `tool-surface` | TOOL-1 (mold) | S4 + S6 | Master surface | **Why S1 on composite?** - S1 is the element face on the outer surface of the composite - This is the face that physically touches the mold - S2 is the inner surface (where pressure is applied) **Why S4+S6 on TOOL?** - The mold is an L-shaped bracket with two contact faces - S4 and S6 correspond to the two inner faces of the mold L-shape - Both faces must be included to capture full contact ## Contact Interaction Property ``` *Surface Interaction, name=INTER-1 *Friction 0.45 # Step vis: viscous state friction *Surface Behavior, pressure-overclosure=HARD ``` ## Temperature-Dependent Friction Friction changes with material state (temperature-dependent). Each step has a different friction coefficient: | Step | Temperature Range | Material State | Friction Coefficient | |------|------------------|----------------|---------------------| | vis | 25°C → 150°C | Viscous (rubbery) | 0.45 | | rub | 150°C → 180°C | Rubbery | 0.20 | | glassy | 180°C → 25°C | Glassy (cured) | 0.169 | | sp | 25°C | — | N/A (contact removed) | **Physics behind friction change**: - **Viscous (0.45)**: High friction because resin is viscous and sticky; composite strongly adheres to mold - **Rubbery (0.20)**: Lower friction as resin becomes more rubbery; some slip occurs - **Glassy (0.169)**: Lowest friction as material vitrifies; cured composite can slide more freely on mold **How to implement per-step friction**: ``` *Step, name=vis *Change Friction, interaction=INTER-1 0.45, *Step, name=rub *Change Friction, interaction=INTER-1 0.20, *Step, name=glassy *Change Friction, interaction=INTER-1 0.169, ``` ## HARD Contact Behavior ``` *Surface Behavior, pressure-overclosure=HARD ``` - **HARD**: Standard hard contact — no penetration allowed, no tension - Pressure transfers only when surfaces are in contact - Gap opens when pressure goes to zero (no adhesion) ## Contact in Springback Step (sp) In the sp step, contact is **completely removed** via Model Change: ``` *Step, name=sp *Model Change, remove TOOL-1.EL # Remove mold elements *Model Change, remove TOOL-1, com-surface # Remove composite contact surface assignment *Model Change, remove TOOL-1, tool-surface # Remove tool contact surface assignment ``` After Model Change: - No contact pair exists - No friction - Composite is free to deform (constrained only by Set-2) - Residual stresses drive springback deformation ## Why Contact Creates Asymmetric Springback 1. **Friction varies spatially**: Different regions of the composite experience different normal pressures, leading to varying frictional resistance 2. **L-bracket geometry**: The corner region has higher contact pressure than the arm tips, creating non-uniform constraint 3. **Thermal expansion**: During heating, the composite expands and slides against the mold; friction resists this sliding asymmetrically 4. **Demolding release**: When the mold is removed, the stored frictional energy releases unevenly, causing asymmetric deformation 5. **Result**: Maximum displacement at free edges (arm tips), minimum at the corner — this is the correct physical pattern ## P8_only vs P8_mold Contact Comparison | Aspect | P8_mold (Correct) | P8_only (Incorrect) | |--------|-------------------|---------------------| | Contact pair | com-surface ↔ tool-surface | None | | Friction | 0.45 → 0.2 → 0.169 | None | | Contact behavior | HARD | None | | Demolding | Model Change removes contact | No demolding | | Composite constraint | Friction (allows slip) | ENCASTRE (no slip) | | Springback pattern | Asymmetric (correct) | Center-symmetric (wrong) | ## Common Errors | Error | Cause | Fix | |-------|-------|-----| | Penetration in ODB | Contact not properly defined | Verify surface assignments (S1 on composite, S4+S6 on tool) | | No springback | Contact not removed in sp | Add `*Model Change, remove` for TOOL elements and surfaces | | Convergence issues | Friction too high | Check friction values: 0.45/0.2/0.169 for vis/rub/glassy | | Symmetric deformation | No contact (P8_only model) | Use P8_mold_V2.inp with proper contact pair | | CPRESS = 0 everywhere | Wrong surface pair | Verify master/slave assignment; tool is master |