LS-DYNA Vehicle Crash Simulation: Frontal, Side, and Rear Impact Analysis

LS-DYNA Vehicle Crash Simulation: Frontal, Side, and Rear Impact Analysis

I've been involved in vehicle crash simulation for years, and LS-DYNA is the tool everyone in automotive uses — there's really no debate about that. What I want to share here isn't just the setup steps, but the things that actually make your crash results match physical tests. Because honestly, getting a crash simulation to correlate with a sled test is one of the hardest things I've done in my career.

Full Vehicle Model

Model Components

1. Body in white (BIW): Spot-welded sheet metal panels
   • Elements: S4R (Belytschko-Tsay shells)
   • Thickness: 0.7-2.5mm
   • Material: *MAT_PIECEWISE_LINEAR_PLASTICITY (MAT_024)
2. Closures: Doors, hood, trunk lid
   • Shell elements with hinges
3. Frame rails: Front and rear longitudinal rails
   • Thicker shells (1.8-3.0mm) for energy absorption
4. Suspension: Springs, dampers, control arms
   • Beam and shell elements
   • Spring elements (*ELEMENT_DISCRETE)
5. Powertrain: Engine, transmission (rigid or deformable)
   • Rigid: *MAT_RIGID (fast, for non-crushing components)
   • Deformable: For engine block intrusion analysis
6. Wheels and tires: Rigid or deformable
7. Seats: Frame + foam + trim
8. Interior: Dashboard, door panels, headliner

Spot Welds

1. *CONSTRAINED_SPOTWELD:
   • Connects two shell panels at a point
   • Parameters:
     • SN: Spot weld ID
     • N1, N2: Nodes on each panel
     • SN: Strength (force-based failure)
2. Or use beam elements:
   • *ELEMENT_BEAM between welded nodes
   • *MAT_SPOTWELD (MAT_100) with failure criterion
3. Spot weld failure:
   • Force-based: F > Ffail → weld breaks
   • Typical: 3000-8000N (steel sheet spot weld)
4. Check: Spot weld failures in post-processing (critical for structural integrity)

Adhesive Joints

1. *MAT_COHESIVE_MIXED_MODE (MAT_138):
   • For adhesive bonds (hem flanges, structural adhesive)
   • Traction-separation law
   • Mixed-mode failure (Mode I + Mode II)
2. Parameters:
   • Normal strength: tN (MPa)
   • Shear strength: tS (MPa)
   • Fracture energy: GIC, GIIC (mJ/mm²)

Barrier Models

Rigid Wall

1. *RIGIDWALL_PLANAR:
   • Define wall plane (point + normal)
   • Infinite rigid wall
2. Parameters:
   • NS: Normal direction (e.g., (0,1,0) for wall in XZ plane)
   • X0, Y0, Z0: Point on wall
3. Use for: FMVSS 208 frontal barrier (rigid wall)

Deformable Barrier

1. *MAT_RIGID for barrier frame
2. *MAT_PIECEWISE_LINEAR_PLASTICITY for barrier face (honeycomb)
3. FMVSS 214 side impact barrier (MDB):
   • Moving deformable barrier
   • Mass: 1367 kg
   • Velocity: 50 km/h
   • Honeycomb face with defined stiffness

Pole Impact

1. *RIGIDWALL_CYLINDRICAL:
   • Rigid cylinder (diameter = 254mm for FMVSS 214 pole)
2. Parameters:
   • Radius: 127mm
   • Axis direction: Vertical (Y)
3. Use for: Side pole impact (roof crush, side intrusion)

Crash Scenarios

Frontal Rigid Barrier (FMVSS 208)

1. Velocity: 56 km/h (35 mph) or 64 km/h (40 mph, EuroNCAP)
2. Barrier: Rigid wall, 0° or 30° angle
3. Impact direction: Frontal (X-direction)
4. Duration: 100-150 ms
5. Measurements:
   • Acceleration: At B-pillar, seat cross-member, engine cradle
   • Intrusion: Firewall, toe board, steering column
   • Dummy response: Head, chest, pelvis acceleration
6. Criteria:
   • Chest acceleration: < 60G
   • Chest deflection: < 63mm
   • Femur force: < 10kN
   • HIC (Head Injury Criterion): < 1000

Side Impact (FMVSS 214)

1. MDB velocity: 50 km/h (31 mph)
2. MDB mass: 1367 kg
3. Impact direction: Lateral (Y-direction)
4. Duration: 80-120 ms
5. Measurements:
   • Door intrusion: At chest, abdomen, pelvis levels
   • B-pillar intrusion: Maximum lateral displacement
   • Dummy response: Thorax, abdomen, pelvis
6. Criteria:
   • Thoracic TTI: < 85G (50th percentile male)
   • Pelvic acceleration: < 130G
   • Door intrusion: < 381mm (15 inches)

Side Pole Impact (FMVSS 214)

1. Velocity: 32 km/h (20 mph)
2. Pole: Rigid, 254mm diameter
3. Impact angle: 75° from vehicle centerline
4. Measurements:
   • Door intrusion: At chest level
   • Head contact: With pole (HIC)
5. Criteria:
   • HIC: < 1000
   • Thorax deflection: < 42mm

Rear Impact (FMVSS 301)

1. Velocity: 80 km/h (50 mph) for rear moving barrier
2. Barrier mass: 1367 kg (MDB)
3. Impact direction: Rear (−X direction)
4. Duration: 100-150 ms
5. Measurements:
   • Fuel system integrity: No leakage
   • Rear intrusion: Seat, fuel tank area

Dummy Models

ATD (Anthropomorphic Test Device)

1. Hybrid III 50th percentile male:
   • Mass: 78.2 kg
   • Height: 175 cm
   • Use for: Frontal crash
2. Hybrid III 5th percentile female:
   • Mass: 49.5 kg
   • Height: 152 cm
   • Use for: Frontal crash (small occupant)
3. SID-IIIs (Side Impact Dummy):
   • Use for: Side impact
4. Q-dummies (EuroNCAP):
   • Q3, Q6, Q10 (child dummies)
   • Use for: Child restraint evaluation

Dummy Positioning

1. Position dummy in seat:
   • H-point: At defined seat reference
   • Head: Upright, facing forward
   • Hands: On steering wheel (driver) or lap (passenger)
   • Feet: On floor or pedals
2. Seatbelt routing:
   • Across shoulder and lap
   • Through dummy pelvis and chest

Dummy Injury Criteria

1. HIC (Head Injury Criterion):
   • HIC = max[(1/(t2-t1)) ∫a(t)dt]².5 × (t2-t1)
   • a: Head resultant acceleration (G)
   • t2-t1: Time window (36ms for HIC_36, 15ms for HIC_15)
   • Limit: HIC < 1000
2. Chest acceleration: < 60G (3ms clip)
3. Chest deflection: < 63mm (Hybrid III)
4. Neck injury (Nij):
   • Nij = Fz/Fzc + My/Myc
   • Limit: Nij < 1.0
5. Femur force: < 10kN

Restraint Systems

Seatbelt

1. *MAT_SEATBELT (MAT_195):
   • 1D elements (seatbelt webbing)
   • Properties:
     • Stiffness: Force per unit strain
     • Pretensioner: Initial tension force
     • Load limiter: Force at which belt yields
2. Routing:
   • Anchor point (floor)
   • D-ring (B-pillar)
   • Shoulder and lap segments
   • Buckle

Airbag

1. *AIRBAG_PARTICLE:
   • Particle method for gas dynamics
   • Inflator: Mass flow rate and temperature vs. time
2. *AIRBAG_SIMPLE_PRESSURE:
   • Simplified pressure-volume model
   • Faster but less accurate
3. Parameters:
   • Inflator curve: Mass flow (kg/s) vs. time
   • Gas: Molecular weight, specific heat ratio
   • Vent holes: Outflow area
4. Airbag deployment:
   • Crash sensor triggers at t = 10-20ms
   • Inflator fires: t = 15-25ms
   • Bag fully inflated: t = 30-40ms
   • Occupant contact: t = 40-60ms

Post-Processing

Acceleration Pulse

1. B-pillar acceleration: Primary crash severity metric
   • Plot: Acceleration (G) vs. time (ms)
   • Shape: Should show controlled deceleration
   • Peak: Typically 30-50G (frontal), 40-80G (side)
2. Filter: SAE J211 CFC 60 (filter for structural acceleration)

Intrusion

1. Firewall intrusion: Distance firewall moves rearward
   • Measure: Initial to final position at toe board
   • Limit: < 125mm (frontal, at toe board)
2. Steering column intrusion: Rearward displacement
   • Limit: < 125mm
3. Door intrusion: Inward displacement (side impact)
   • Measure: At chest, abdomen, pelvis levels

Energy Absorption

1. By component: Energy absorbed by each part
   • *DATABASE_MATSUM: Per-part energy
   • Identify: Which components absorb most energy
   • Optimize: Increase energy absorption in crush zones
2. Total energy: Initial KE = IE + CE + HG + EW
   • Initial KE = 0.5 × m × v²
   • Example: 1500 kg at 56 km/h (15.56 m/s)
   • KE = 0.5 × 1500 × 15.56² = 181,500 J = 181.5 kJ

Velocity Profile

1. Vehicle velocity: vs. time
   • Starts at impact velocity (e.g., 56 km/h)
   • Decelerates to 0 (or rebounds)
   • Duration: 80-120ms (frontal)
2. Delta-V: Change in velocity
   • For rigid barrier: ΔV = Vinitial (full stop)
   • For deformable barrier: ΔV < Vinitial (rebound)

Verification Checklist

• [ ] Vehicle mass matches test (±2%)
• [ ] Center of gravity matches test
• [ ] Spot welds are correctly placed and fail at correct force
• [ ] Material stress-strain curves include strain rate effects
• [ ] Barrier mass and velocity match regulation
• [ ] Dummy is positioned correctly (H-point, head angle)
• [ ] Seatbelt is routed and pretensioned correctly
• [ ] Airbag deployment timing is correct
• [ ] Acceleration pulse shape matches test (if available)
• [ ] Intrusion values match test (if available)
• [ ] Energy balance is satisfied (KE = IE + CE + HG)
• [ ] Hourglass energy < 5% of internal energy

Wrapping Up

If you're getting into crash simulation, my biggest advice is to correlate with physical test data early and often. I've seen beautiful-looking simulations that were completely wrong because the spot weld failure force was off or the material strain rate parameters weren't calibrated. Get the vehicle mass right (within 2%), make sure your material cards include strain rate effects, and check your acceleration pulse against a physical test before you trust any injury numbers. Once your baseline correlates, you can confidently evaluate design changes — and that's where crash simulation saves months of development time.