| name | fea-contact-mechanics |
| description | FEA contact mechanics — contact algorithms (penalty, Lagrange, augmented Lagrange), Hertz validation, friction models, contact convergence, ABAQUS/ANSYS contact settings, press-fit, gasket contact, mesh requirements. |
| metadata | {"priority":7,"promptSignals":{"phrases":["FEA contact","contact mechanics FEA","contact simulation","Hertz contact FEA","ABAQUS contact","press fit FEA"],"minScore":3}} |
FEA Contact Mechanics — Complete Skill
Contact Formulations
1. Penalty Method
Principle: allow small interpenetration; apply restoring force proportional to penetration depth
F_contact = k_penalty × δ_overlap [k_penalty = stiffness parameter]
Advantages: no extra DOF; computationally efficient; robust convergence
Disadvantages: interpenetration exists (magnitude: δ ≈ typical_force / k_penalty); accuracy depends on k selection
ABAQUS: SOFT=PENALTY under *CONTACT PAIR or in General Contact; default for implicit
2. Lagrange Multiplier Method
Principle: add extra DOF (pressure) to enforce exact no-penetration constraint
Advantages: no interpenetration; accurate contact pressure
Disadvantages: larger system; over-constraint risk; can cause chattering (contact/open oscillation)
ABAQUS: ENFORCE=LAGRANGE; more stable with augmented Lagrange
3. Augmented Lagrange (Hybrid — Most Common)
Principle: penalty + Lagrange update each increment; converges to near-zero penetration
Best balance of accuracy and convergence
ABAQUS: *SURFACE INTERACTION + *CONTACT PROPERTY (default augmented Lagrange for general contact)
Contact tolerance (HCRIT): penetration tolerance; default = 1/100 of characteristic length
Tighten: EPSN = 0.001–0.01 (relative to element size)
ABAQUS Contact Setup
General Contact (recommended for most problems):
*CONTACT → *CONTACT INCLUSIONS → automatically includes all surfaces
Robust; handles self-contact; complex geometry
Suitable: crash, metal forming, assemblies with many contact pairs
Contact Pair:
*CONTACT PAIR, INTERACTION=interaction_name
Define master (stiffer, coarser mesh) and slave surfaces
Master: rigid/stiffer body; Slave: deformable/finer mesh
More control; faster for simple 2-surface problems
Contact Property (interaction property):
Normal: *CONTACT PROPERTY → *SURFACE BEHAVIOR → PRESSURE-OVERCLOSURE=HARD (default) or SOFT (penalty)
Tangential: *FRICTION → μ_friction (Coulomb)
Separation: allow separation (default) or NO SEPARATION (no-open after contact)
Slave node constraints:
Node-to-surface: slave nodes cannot penetrate master surface; easy setup; some accuracy loss for coarse slave mesh
Surface-to-surface: more accurate pressure distribution; both surfaces exchange constraint; preferred
ANSYS Contact Setup
Contact element pairs:
CONTA174 (3D surface, slave) + TARGE170 (3D target, master)
KEYOPT(2): contact algorithm: 0=augmented Lagrange; 1=penalty; 3=Lagrange
KEYOPT(10): contact stiffness update: 2=each iteration (recommended for complex)
Contact stiffness (FKN): relative factor (0.001–10); scale by normal stiffness
FKN = 1.0 (default; good for most); FKN = 0.1–0.01 (softer bodies, better convergence)
Pinball region: sphere around slave node; contact only detected within pinball
Increase PINBALL if contact misses; reduce if false contact detected
Hertz Contact Validation
Always validate against analytical Hertz before complex problems:
Sphere of radius R pressing on flat; elastic properties E₁, ν₁, E₂, ν₂; load P
a_analytical = (3PR/(4E*))^(1/3); p₀ = 3P/(2πa²)
FEA requirements for Hertz accuracy:
Mesh: at least 5–6 elements across contact radius a (a typically small; mesh can be very fine)
Symmetry: use symmetry to reduce model to 1/4 or 1/8 sphere
Element type: C3D8R (reduced integration) or C3D20 (full integration); avoid C3D4 near contact
Contact pressure tolerance: FEA p₀ should match analytical within ±5%
Common validation error: insufficient mesh at contact zone → under-predicted p₀; refine until convergent
Press-Fit Analysis
Interference fit assembly:
Initial: inner radius of hub > outer radius of shaft (deliberate interference Δ = 0.05–0.2 mm)
After assembly: contact pressure p on interface
p_analytical = Δ × E_eff / D [simplified; D = interface diameter; E_eff from thick-wall cylinder solution]
FEA approach for press-fit:
- Create separate bodies with actual interference (overlap in initial geometry)
- Contact at interface (augmented Lagrange); separation NOT allowed (*NO SEPARATION or CONTRACTION)
- Apply displacement (push hub onto shaft) or thermal loading
- Extract contact pressure and hoop stress in hub
Stress state:
Hub inner surface: σ_hoop = p × (D_o² + D_i²) / (D_o² - D_i²) [tensile; may yield first]
Shaft outer: σ_hoop = -p [compressive; beneficial for fatigue]
Axial retention force:
F_retention = μ × p × π × D × L [N; μ = friction coefficient at interface; L = fit length]
Gasket and Sealing Contact
Gasket: compressible; nonlinear pressure-closure relationship
ABAQUS: *GASKET SECTION; define closure-pressure curve from test data
Leakage: not modeled directly in FEA; check minimum contact pressure > seating stress from ASME
ASME gasket seating:
Minimum stress at bolt up: m_G × design pressure (m_G = gasket factor; 2.0 for spiral wound)
Minimum for seating: y_G = 10,000 psi (gasket seating stress; from ASME Code)
Compressed gasket contact area:
A_contact = π/4 × (D_o² - D_i²) [annular area]
Contact pressure = F_bolt_total / A_contact → compare to minimum required
Frictional Contact Convergence
Sticking vs. sliding:
Coulomb: |τ| < μ × p → stick; |τ| = μ × p → slip
Sticking DOF: no relative motion; sliding: relative motion at interface
Convergence difficulties:
Chattering: alternating contact/open at node → increase damping (stabilize) or increase penalty
Sliding instability: stick-slip oscillation → increase tangential stiffness or reduce μ slightly
Over-constraint: rigid body motion in contact → add weak springs or fix DOF
ABAQUS stabilization for contact:
*CONTACT CONTROLS, STABILIZE: adds numerical viscous damping to contact; use FACTOR=0.001–0.01
Removes rigid body motion; helps establish initial contact; turn off after first step (STABILIZE=0)
Contact State Extraction
Post-processing contact:
CPRESS: contact pressure [MPa] → for stress analysis
CSHEAR: contact tangential shear stress [MPa]
COPEN: contact gap/opening [mm] (positive = open; negative = penetration)
CSLIP: sliding distance [mm]
STATUS: 0 = no contact; 1 = sliding; 2 = sticking
Max contact pressure critical locations:
Hertz: at center of contact zone; for conforming contact: may vary
Edge contact: high stress concentration at pad edges; fillet design critical
Standards
| Standard | Scope |
|---|
| ASME V&V 10 | Guide for verification and validation in computational solid mechanics |
| ASME V&V 40 | V&V for medical devices |
| ISO 10810 | Static testing of implants (includes contact simulation validation) |
| ABAQUS User Manual 6.14 | Contact chapter — definitive reference |
Output
Provide: contact algorithm (augmented Lagrange/penalty), contact type (general/contact pair), master/slave assignment, friction coefficient μ, contact tolerance HCRIT [mm], mesh density in contact zone [elements/mm], peak contact pressure CPRESS [MPa] vs. Hertz analytical (validation error [%]), contact area [mm²], contact gap (no penetration check), frictional shear stress CSHEAR [MPa], convergence behavior (any chattering/stabilization used), press-fit retained force [kN] (if applicable), gasket minimum contact pressure vs. ASME requirement, and applicable standard (ASME V&V 10, ABAQUS manual).
