Crumple Zone Design for Convertible Vehicle Rigidity

Overview of Technical Issues:

The convertible vehicle body frame provides insufficient structural constraint to the crumple zone due to the absence of roof reinforcement, resulting in unpredictable and unreliable energy absorption during collisions that compromises occupant protection; the goal is to optimize the crumple zone design to achieve controlled deformation and effective crash energy management while maintaining the open-top configuration requirements.

Solution directions generated for this problem

Problem Direction 1 :

ImproveFrame structural constraint strength
VS
ConstraintFrame reinforcement mass

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Joining structure
Innovative Solution Refine solution

Modular high-strength node reinforcement for convertible frame constraint

Divide frame into discrete load zones with targeted reinforcement
How to solve :
  • Segment A-pillar and sill into three discrete reinforcement modules: upper hinge zone (150mm, 2.5mm wall), mid-section (standard 1.8mm), lower rocker junction (200mm, 3.0mm wall) — concentrating mass only at critical load transfer points
  • Install precision-cast aluminum nodes (AlSi10Mg, yield strength ≥240 MPa) at A-pillar-to-sill junctions using single-mass laser welding per patent US10435081B2, achieving 150kN load capacity at 55% steel mass
  • Design floor pan with segmented cross-braces (carbon fiber tubes, 40mm diameter, 2mm wall) positioned at front seat mounts and rear bulkhead only, providing 72% hardtop torsional rigidity while adding only 18kg total reinforcement mass
Expected Effect : Torsional rigidity 70-80% of hardtop; total mass penalty reduced to 28kg (vs. 45-65kg uniform reinforcement); bending resistance >150kN at critical nodes
Risk Control :
  • aluminum-steel galvanic corrosion at welded joints
  • laser weld penetration consistency (target ±0.3mm depth)
  • carbon fiber tube-to-steel interface bonding durability under cyclic loading

Problem Direction 2 :

ImproveFrame structural constraint strength
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #27 Cheap short-living objects
Cross-domain applicability Assess applicability
Nucleating agent for polyolefin resin, nucleating agent composition for polyolefin resin containing same, master batch for polyolefin resin, polyolefin resin composition, molded article thereof, film thereof, method for producing porous film, and package
Innovative Solution Refine solution

Replaceable precision crash node inserts for tolerance-relaxed frame assembly

Tolerance-insensitive frame with precision nodes
How to solve :
  • Design replaceable precision-machined crash node inserts at A-pillar-to-sill and floor-to-sill junctions with ±0.3mm tolerance, while surrounding frame uses standard ±2.0mm automotive tolerance
  • Inserts are hardened steel socket assemblies (yield strength ≥800 MPa) with self-centering tapered interfaces that absorb ±1.5mm positional variation during bolt-up torque (120–140 Nm)
  • Post-assembly laser weld the insert perimeter to parent frame, creating controlled load path nodes achieving 72–78% hardtop torsional rigidity without precision-machining the entire structure
Expected Effect : Frame precision cost −60%, constraint strength 75% of hardtop, assembly time −40%
Risk Control :
  • insert-to-frame weld quality variation
  • socket wear after multiple crash-replacement cycles
  • tolerance stack-up in multi-insert assemblies

Problem Direction 3 :

ImproveCrumple zone load distribution capacity
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
motor
Innovative Solution Refine solution

Pre-stressed load channel geometry for tolerance-insensitive crumple zone

Pre-form residual stress patterns in crumple zone rails during assembly to guide deformation paths
How to solve :
  • Apply controlled pre-compression (80-120 MPa) to longitudinal rails during welding fixture stage, creating residual stress gradients that define buckling initiation zones independent of ±1.0mm geometric variations
  • Integrate laser heat treatment zones at 200mm intervals along rail length, generating hardness bands (380-420 HV core, 280-320 HV transition) that channel forces through predetermined paths regardless of wall thickness variations up to ±0.8mm
  • Install self-centering tapered socket joints at A-pillar/sill junctions with 3° taper angle, achieving load path alignment within 0.3° angular tolerance even with ±1.5mm positional mating errors, maintaining >150kN transfer capacity
Expected Effect : Load path predictability ±12%; manufacturing tolerance relaxed to ±1.0mm; assembly time -30%
Risk Control :
  • residual stress relaxation over thermal cycles
  • hardness gradient consistency across production batches
  • socket joint wear under repeated load testing

Problem Direction 4 :

ImproveEnergy absorption predictability
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Bonding wire for semiconductor device
Innovative Solution Refine solution

Thermal gradient crumple zone with post-assembly property tuning

Thermal gradient processing eliminates precision dependency
How to solve :
  • Apply localized laser heat treatment post-assembly to create hardness gradients (HV 180-350) in crumple zone rails, establishing predictable buckling zones independent of ±1.5mm geometric variations
  • Use infrared thermography mapping to measure as-built geometry, then program laser path (scan speed 8-15 mm/s, spot diameter 4-6mm, power 800-1200W) to compensate dimensional deviations by adjusting local yield strength distribution
  • Install hardness verification stations measuring 5 points per rail (acceptance: ±8% from target gradient profile), ensuring energy absorption consistency ±12% across NCAP protocols without tightening manufacturing tolerances
Expected Effect : Energy absorption deviation ±12%, manufacturing tolerance relaxed to ±1.5mm, cost reduction 18-22%
Risk Control :
  • laser parameter calibration drift
  • thermal distortion in thin-wall sections
  • hardness gradient measurement repeatability

Problem Direction 5 :

ImproveCrumple zone load distribution capacity
VS
ConstraintFrame reinforcement mass

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Reinforcing shank arrangement for footwear sole structure
Innovative Solution Refine solution

Zoned wall thickness crumple zone rails with geometric load channels

Divide rails into optimized zones by load
How to solve :
  • Segment longitudinal crumple zone rails into three discrete thickness zones: 3.2mm at crush initiator (first 150mm), 1.8mm in mid-deformation section (300mm), 2.6mm at passenger cell interface (200mm) to handle >150kN peak loads with targeted material placement
  • Integrate pre-formed geometric load channels into floor pan using laser-cut raised ribs (height 8mm, width 12mm) and strategic lightening holes (Ø40mm, staggered pattern) that guide forces through predetermined paths without adding thickness
  • Apply localized laser heat treatment (1064nm fiber laser, 2kW power, scan speed 15mm/s) to create hardness gradients (HV 420 at initiator zones, HV 280 in deformation zones) ensuring buckling sequence control with ±1.2mm geometric tolerance instead of ±0.5mm
Expected Effect : Total reinforcement mass reduced to 28-32kg (52% reduction vs uniform reinforcement); >150kN load capacity maintained; ±12% energy absorption consistency across NCAP protocols
Risk Control :
  • laser heat treatment depth variation beyond ±0.15mm
  • geometric rib forming springback exceeding 0.8mm
  • zoned thickness transition stress concentration
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