Development of a lightweight car body, using sandwichdesign
Michael Kriescher, Simon Brückmann, Gundolf Kopp
German Aerospace Center, Stuttgart, Germany
Research field: Lightweight and Hybrid
Design Methods
14.04.2014
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Index
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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
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DLR – Overview
DLR's mission:
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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
SECURITY
TRANSPORT
ENERGY
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The departments of the Institute for Vehicle Concepts
Vehicle systems and
technology assessment
Vehicle energy
concepts
Alternative energy
conversion
Lightweight and hybrid
construction
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Innovative vehicle concepts for road and rail
FK designs and demonstrates innovations for the vehicle concepts and technologies of future
compliant transport systems
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Index
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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
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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
Vehicle structure
Assembly
Component
Sandwich
structures
Basic materials
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Index
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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
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Dynamic Testing of a foam filled hybrid beam
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Weight-specific energy absorption is
three times higher, compared to a
hollow beam
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Dynamic testing results in a slightly
higher force level
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Development of a ring-shaped frame for a lightweight
car body
Absorption of
crash energy
through elongation of material
Stabilisation of
the cross
section
A-ring shaped structure
should lead to an even better
distribution of plastic strain
Application:
Ring-shaped frame of a lightweight
vehicle concept
(metal-monocoque structure)
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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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Index
• 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
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Schematic procedure
Core Material
Sandwich
Analysis of polymer foams under
pressure loading
Analytical calculation of failure
behavior of sandwich elements
Material parameters
Determination of material
parameters in uniaxial
compression
Preparation of failure-mode-maps
Compression testing with
sandwich elements to validate
failure behavior
Transfer of stress-strain curves in
FEM
Simulation
Matching between simulation and
real material tests
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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
Wrinkling
Core thickness [mm]
Bulging (shear)
Global = shear
Wrinkling = global
Wrinkling = shear
Euler buckling and
shear failure of core
material
Core density [kg/m³]
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Sandwich Elements in In-plane
Load Case
Global crippling
Shear failure of core material
Wrinkling
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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Application Examples
Tests on Structural Components
• Box structure
• Cross structure
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Index
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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
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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
- Relatively uniform force-deformation-curve
- Integration of various functions in one part:
- Regular folding of the aluminium layers
- Loads from the chassis
- Support for various drive-train
components
- Energy absorption in frontal crash
load cases
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Index
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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
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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
Thank you for your attention!