Development of a lightweight car body, using sandwich-
design
Michael Kriescher, Simon Brückmann, Gundolf Kopp
German Aerospace Center, Stuttgart, Germany
Research field: Lightweight and Hybrid
Design Methods
14.04.2014
• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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DLR – Overview
DLR's mission:
• exploration of the Earth and the solar system
• research aimed at protecting the environment
• development of environmentally-friendly technologies
to promote mobility, communication and security.
7.700 employee are working at 32 research institutes and
facilities in n 9 locations and 7 branch offices.
SPACE AERONAUTICS TRANSPORT ENERGY
SECURITY
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The departments of the Institute for Vehicle Concepts
Alternative energy
conversion
Vehicle energy
concepts
Lightweight and hybrid
construction
Vehicle systems and
technology assessment
1 2 3 4
Innovative vehicle concepts for road and rail
FK designs and demonstrates innovations for the vehicle concepts and technologies of future
compliant transport systems
www.DLR.de • Chart 4
• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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Car body design variants
• Steel-shell design, e.g. VW Golf:
• Comparatively high weight
• Large number of parts with complex shape (ca. 200-300)
• Very low production costs at very high lot numbers
(approx. 1 million/year)
• Aluminium-extrusions, e.g. Lotus Elise:
• Low weight due to low density of aluminium
• Simple parts, but relatively large number of parts
• Monocoque-design, e.g. Lamborghini Aventador:
• Fiber reinforced materials -> Very low weight, very low
number of parts
• Very high material and processing costs, difficult behaviour
during side impact and missuse cases
• Light weight car body of the DLR: „Metal-Monocoque“-design:
• Very low weight, low part number
• Conventional materials, frequent use of sandwich parts
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Metal-monocoque car body: Development targets / objectives
• Very low weight (86 kg)
• Low part number due to high functional integration: approx. 50 parts
per car body at close-to-series production of approx. 50 000 car
bodies per year
• Use of metallic materials with foam cores -> comparatively low costs
for materials and processing
• High damage tolerance due to the high ductility of the metallic shells
• Good passive safety due to new design approaches and deformation
mechanisms
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Sandwich-Lightweight Design
Overview Project Content – Development Levels
Basic materials
Sandwich
structures
Component
Assembly
Vehicle structure
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• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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Dynamic Testing of a foam filled hybrid beam
• Weight-specific energy absorption is
three times higher, compared to a
hollow beam
• Dynamic testing results in a slightly
higher force level
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A-ring shaped structure should lead to an even better distribution of plastic strain
Absorption of crash energy through elong-ation of material
Stabilisation of the cross section Application:
Ring-shaped frame of a lightweight vehicle concept (metal-monocoque structure)
Development of a ring-shaped frame for a lightweight
car body
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Crash Simulation
• Intrusion and deceleration are similar to the state of the art
• Material models must be evaluated
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Euro-NCAP polecrash
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End of part 1
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• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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Schematic procedure
Analysis of polymer foams under
pressure loading
Determination of material
parameters in uniaxial
compression
Analytical calculation of failure
behavior of sandwich elements
Transfer of stress-strain curves in
FEM
Preparation of failure-mode-maps
Compression testing with
sandwich elements to validate
failure behavior
Material parameters
Matching between simulation and
real material tests
Core Material Sandwich
Simulation
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Compression Tests on Polyurethane
Foams
Density 30 kg/m³ Density 300 kg/m³
After testing
High elastic behavior Brittle behavior
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Failure-Mode-Maps
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
30 60 90 120 150 180 210 240 270 300
Ke
rnd
icke
[m
m]
Kerndichte [kg/m³]
Kombi=Schub
Knittern=Kombi
Knittern=Schub
Knittern
Schubbeulen
Eulerknicken und
Kernscheren
Global = shear
Wrinkling = global
Wrinkling = shear
Core density [kg/m³]
Co
re t
hic
kn
ess [
mm
]
Wrinkling
Bulging (shear)
Euler buckling and
shear failure of core
material
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Global crippling Shear failure of core material Wrinkling
Sandwich Elements in In-plane
Load Case
Stand Februar 2013
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Tests on Planar Sandwich Elements
• Symmetric wrinkling with holes and horizontal cuttings in both layers
• Asymmetric wrinkling with vertical cuttings and various wave lengths in
the layers
Instability of load transferring path between the not cutted sections of
the layers
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• Box structure
• Cross structure
Application Examples
Tests on Structural Components
Stand Februar 2013
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• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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Front Structure
General Information
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Front Structure
Static Tests
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Testing of components: Sandwich front structure
- Weight of the front structure: 12 kg
- Integration of various functions in one part:
- Loads from the chassis
- Support for various drive-train
components
- Energy absorption in frontal crash
load cases
- Relatively uniform force-deformation-curve
- Regular folding of the aluminium layers
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• Introduction of the institute of vehicle concepts
• State of the art and goals for the development
• Development of the passenger compartment
• Mechanical properties of sandwich structures
• Development of the front structure
• Current state of the project and further proceeding
Index
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State of the project
• First car body demonstrator has been built
• Crash test of a component (front structure) has been performed
• First estimate for the manufacturing cost of a car body: 570 €
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Further proceeding
• Crash test of other components
• Crash test of the entire car body on the DLR‘s crash test facility
• Build-up of a rolling prototype
• Development of the technology for series production
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Thank you for your attention!
