Crumple Zone Design for Crash Force Limiting in Structures

Overview of Technical Issues:

The energy-absorbing structure in the crumple zone insufficiently limits the magnitude of crash forces transmitted to protected compartments during collision, resulting in excessive peak loads that risk occupant injury or component damage; the goal is to optimize the structure to control force transmission within safe thresholds while maximizing energy absorption through controlled progressive deformation.

Solution directions generated for this problem

Problem Direction 1 :

ImprovePeak force limitation effectiveness
VS
ConstraintPackaging volume requirement

Inspiration 1 : Cross-domain reference

Application Principle: #7 Nested doll
Cross-domain applicability Assess applicability
Driving system for controlling the rotation of an object about two perpendicular axes of rotation and rehabilitation machine for rehabilitation of the lower limbs and the trunk incorporating such a driving system
Innovative Solution Refine solution

Coaxial telescoping crush can for peak-force control in fixed package space

Nested stroke in same space
How to solve :
  • Build 3-stage coaxial crush can with outer, mid, inner tubes and low-friction guides so 240mm package yields 360-400mm effective stroke
  • Use DP780 or 6061-T6 tubes, wall 1.2/1.0/0.8mm, radial clearance 0.35-0.55mm, trigger beads 6-8mm pitch, dry-film lube 8-12um, laser-welded end stops
  • Validate by dynamic crush QC: peak force CV <=8%, trigger depth 0.30+/-0.05mm, tube straightness <=0.4mm/300mm, collapse onset 15-20kN per stage, 100% vision plus 1/200 sled test
Expected Effect : Peak force -25 to -35%, energy +30%, package unchanged, mass +5% max, decel pulse smoother by 20%
Risk Control :
  • tube jamming from burrs
  • stage force overlap too high
  • weld distortion shifts clearances

Problem Direction 2 :

ImproveDeformation progression controllability
VS
ConstraintManufacturing complexity

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Article of footwear with elongated shock absorbing heel system
Innovative Solution Refine solution

Modular bolt-together crush box system with standardized geometric triggers

Divide crumple zone into independent modules with simple geometry
How to solve :
  • Segment crumple zone into 4-6 standardized crush box modules (each 150-200mm length), connected via bolt-together interfaces with M10 Grade 8.8 fasteners at 80mm spacing, enabling independent fabrication and assembly
  • Each module uses constant 1.5mm wall thickness steel tube (ASTM A1008 Grade 50) with stamped circular dimples (diameter 25mm, depth 3mm) at 60mm intervals to trigger progressive folding, eliminating variable thickness or multi-material welding requirements
  • Manufacture via single-stage progressive die stamping with geometric triggers formed simultaneously, then robotic resistance spot welding (6kA current, 200ms duration, 12 spots per seam) for tube closure—total cycle time 45 seconds per module
  • Quality control: dimple depth tolerance ±0.3mm verified by laser scanning (acceptance: 95% within spec), bolt torque 50±5 N·m monitored by digital wrench, crush force verification via drop tower test sampling (target: 80-120kN plateau force, ±10% variation)
Expected Effect : Manufacturing cost -30% vs variable thickness parts; progressive folding efficiency 85-90%; assembly time 8 min per vehicle
Risk Control :
  • dimple position deviation affecting fold sequence
  • bolt joint fatigue under repeated loading
  • module-to-module force transition discontinuity

Problem Direction 3 :

ImproveEnergy absorption capacity
VS
ConstraintMust not deteriorate

Inspiration 1 : Cross-domain reference

Application Principle: #9 Preliminary anti-action
Cross-domain applicability Assess applicability
Method for driving an electro-optic display
Innovative Solution Refine solution

Pre-stressed dual-phase crumple zone with timed stiffness transition

Pre-stressed structure with timed release mechanism
How to solve :
  • Install pre-compressed spring elements (compression rate 15–25%) within crush rails using shear pins rated at 8–12 kN
  • structure exhibits high stiffness (≥80 kN initial resistance) during first 15 ms of impact, then pins fracture to release stored energy enabling progressive collapse at controlled 45–55 kN plateau force
  • Fabricate using dual-hardness steel zones: outer shell heat-treated to 1200 MPa yield strength for initial engagement, inner core at 600 MPa for progressive folding
  • transition occurs automatically as outer shell reaches 12% strain threshold
  • Integrate strain-rate sensitive polymer inserts (polyurea or EPDM rubber, thickness 3–5 mm) between steel layers
  • material exhibits 300% stiffness increase at impact velocities >5 m/s during initial contact (0–20 ms), then softens to baseline modulus as deformation velocity decreases, facilitating controlled yielding phase
Expected Effect : Initial stiffness +85%, peak force reduced 30%, energy absorption +40% within same mass
Risk Control :
  • shear pin fracture timing variance ±3 ms
  • heat treatment zone boundary precision ±2 mm
  • polymer aging degradation over 5 years

Problem Direction 4 :

ImproveEnergy absorption capacity
VS
ConstraintStructural weight

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Green energy-saving fabricated building and construction method thereof
Innovative Solution Refine solution

Modular multi-chamber crush box array with independent energy zones

Divide crumple zone into independent chambers for optimized energy dissipation per unit mass
How to solve :
  • Partition the crumple zone into 4–6 independent hexagonal crush chambers, each 80–120mm in length, connected via shear pins rated at 8–12kN
  • each chamber uses 0.8–1.2mm wall thickness high-strength steel (yield strength 420–550 MPa) with pre-stamped diamond-pattern triggers (depth 2–3mm, spacing 40mm) to initiate progressive folding at predetermined loads
  • chambers activate sequentially as shear pins fail, distributing energy absorption across discrete zones rather than continuous structure
  • Design each chamber with optimized cross-sectional geometry — hexagonal profile provides 18–22% higher specific energy absorption (kJ/kg) than square sections due to corner stress concentration
  • use laser cutting (tolerance ±0.15mm) and robotic TIG welding (penetration depth 1.5–2.0mm) for consistent joint quality
  • Implement graduated chamber stiffness — front chambers use 1.2mm walls for initial impact resistance (peak force 85–95kN), middle chambers 1.0mm (plateau force 65–75kN), rear chambers 0.8mm (final absorption 45–55kN)
  • total system mass reduced by 17–23% versus equivalent monolithic structure while maintaining 45–50kJ total energy absorption
Expected Effect : Energy absorption 45–50kJ; weight reduction 17–23%; peak force controlled ≤95kN
Risk Control :
  • shear pin failure timing variance
  • welding joint strength inconsistency
  • chamber wall thickness tolerance deviation
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