crash-analysis

name	crash-analysis
description	Crash analysis — FMVSS, EuroNCAP/IIHS tests, energy absorption, crush zone design, deceleration pulse, HIC, thoracic criteria, LS-DYNA FEA methodology, occupant kinematics, restraint systems.
metadata	{"priority":7,"promptSignals":{"phrases":["crash analysis","crashworthiness","impact analysis","FMVSS 208","frontal crash","energy absorption crash"],"minScore":3}}

Crash Analysis — Complete Skill

Regulatory Tests and Standards

FMVSS (US Federal Motor Vehicle Safety Standards)

Test	Speed	Configuration
FMVSS 208	56 km/h (35 mph)	Full-width frontal rigid barrier
FMVSS 301	80 km/h (50 mph)	Rear 70% overlap
FMVSS 214	54 km/h (33.5 mph)	Side moving deformable barrier (MDB)
FMVSS 216	Static	Roof crush — 1.5× vehicle weight
FMVSS 305	48.3 km/h	Rear (electric vehicle)

EuroNCAP Tests

Test	Speed	Config	Pass criterion
Frontal ODB	64 km/h	40% overlap, deformable barrier	Chest compression ≤ 50 mm
Side pole	32 km/h	29° angle pole	HIC36 ≤ 650
AEB	20–60 km/h	Active safety scoring	Collision avoidance
Whiplash	16 km/h	Rear sled	Neck injury criteria

IIHS Tests

Test	Speed	Config
Frontal 40% overlap	64 km/h (40 mph)	40% offset deformable barrier
Small overlap	64 km/h	25% offset rigid
Side impact	50 km/h	MDB
Moderate overlap	64 km/h	40% full frontal deformable

Injury Criteria

Head Injury Criterion (HIC)

HIC36 = max over 36 ms window: HIC = [(1/(t₂-t₁)) ∫_{t₁}^{t₂} a(t)dt]^2.5 × (t₂-t₁) [a in g] Limit: HIC36 ≤ 700 (FMVSS 208); HIC15 ≤ 700 (15 ms window)

Chest Criteria

Chest acceleration: 3 ms clip: a_chest ≤ 60 g (FMVSS); EuroNCAP: a_chest ≤ 30 g for 3 ms Chest compression: δ_chest ≤ 76 mm (US); ≤ 42 mm (EuroNCAP frontal, 50 mm alarm) Viscous criterion (VC): VC = V × C(t) ≤ 1.0 m/s [V = compression velocity; C = compression fraction]

Neck Criteria

Nij (normalized neck injury): Nij = F_z / F_zc + M_y / M_yc ≤ 1.0 F_zc = 6806 N (tension); M_yc = 310 N·m (flexion) NIC (neck injury criterion, whiplash): NIC = a_head_rel × 0.2 × 0.0546 + 0.5 × v_rel²

Lower Extremity Criteria

Tibia Index (TI): F_z/F_zc + M_y/M_yc ≤ 1.0 Femur force ≤ 10,000 N (FMVSS 208)

Energy Management

Crush Zone Design

Total energy absorbed: E_total = 0.5 × m × v² × η_transfer [η = fraction going to crush zone] E_total = ∫ F_crush × dδ [area under force-displacement curve]

Mean crush force: F_mean = E_total / δ_crush [design for F_mean × δ_crush = required energy]

Progressive folding (thin-wall tubes): F_mean = 3.5 × σ_y × t^(5/3) × b^(1/3) [for square section; t = wall thickness; b = width] σ_y = material yield strength; b = section width

Energy density (structural materials):

Material	Specific energy [kJ/kg]
High-strength steel (DP780)	10–15
Aluminum 6061	8–12
GFRP	20–40
CFRP	40–80

Crash box (crush initiator): Trigger mechanism (indentations, pre-crush) to initiate controlled folding Fold wavelength: λ ≈ 0.67 × √(t × b)

Deceleration Pulse

Average deceleration: ā = v² / (2δ_total) [δ_total = sum of all crush zones] Target: ā < 30 g (occupant survivable for typical frontal crash)

Pulse shape: Square pulse: minimizes occupant displacement for given deceleration Triangular pulse: typical of vehicle crush; higher peak than square (equivalent ΔV)

Vehicle deceleration tolerance: Limiting structural intrusion: Δ_intrusion ≤ 150 mm (footwell), ≤ 75 mm (firewall)

Occupant Kinematics

Occupant forward motion (relative to vehicle): x_occ = ∫∫ a_vehicle dt² [during crash, before belt loading] Typical: 100–150 mm forward before belt fully loaded

Seatbelt system: Pretensioner: removes 50–75 mm slack at crash detection Load limiter: caps belt force at 4–6 kN to limit chest loading Airbag deployment: 10–20 ms after crash detection; fully inflated by 30 ms

Airbag interaction: Occupant must be > 100 mm from airbag at deployment (out-of-position = injury risk) Deployment speed: 280–320 km/h

FEA Methodology (LS-DYNA)

Model Setup

Element types: Belytschko-Tsay shell (BT, type 2) — default for crash; hourglass control Element size: 5–10 mm for crashworthiness (coarser for full-vehicle BIW = 10 mm) Time step: Δt = 0.9 × L_min / (c × √3) [L_min = minimum element size; c = sound speed; factor 0.9 safety] For steel, 5 mm element: Δt ≈ 1 μs → total crash at 100 ms → 10⁵ steps

Material models: MAT_24 (Piecewise Linear Plasticity): most common for steel; input σ-ε curve up to fracture MAT_58 (Laminated Composite Fabric): for FRP Failure: DUCTILE failure with ε_f defined; elements deleted at failure (erosion)

Contact: CONTACT_AUTOMATIC_SINGLE_SURFACE: general self-contact for sheet metal CONTACT_TIED_SHELL_EDGE_TO_SURFACE: rigid welds Friction coefficient: μ = 0.15–0.20 (steel-steel in crash)

Barrier Models

NCAP deformable barrier (AE-MDB): MAT_MODIFIED_HONEYCOMB material; EEVC standard ODB (frontal): 40% overlap; mesh of barrier available from NHTSA/EuroNCAP

Correlation

Force-displacement: match test corridor ± 15% (corridor = ± 1 standard deviation of tests) HIC: match within ± 5% of test average Pulse: time to peak deceleration ± 3 ms

Standards

Standard	Scope
FMVSS 208	Frontal occupant crash protection
FMVSS 214	Side impact protection
SAE J2980	Crashworthiness evaluation
ECE R94	Frontal impact (ECE regulation, 40% ODB)
ECE R95	Lateral impact
ISO 13232	Motorcycle rider protection

Output

Provide: test type (FMVSS 208/EuroNCAP/IIHS), crash configuration (speed [km/h], barrier, overlap [%]), total energy absorbed E [kJ], mean crush force F_mean [kN], crush zone length δ [mm], deceleration pulse (peak [g], duration [ms]), HIC36 value vs. limit (700), chest compression [mm] vs. limit, Nij, intrusion [mm] vs. limit, material selection for crush zone (σ_y [MPa], specific energy [kJ/kg]), LS-DYNA element size [mm] and time step [μs], and applicable standard (FMVSS 208, ECE R94).