development of a lightweight car body, using sandwich-...

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

www.DLR.de • Chart 2

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


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








Index


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


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


Sandwich-Lightweight Design

Overview Project Content – Development Levels

Basic materials

Sandwich

structures

Component

Assembly

Vehicle structure








Index


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


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


Crash Simulation

• Intrusion and deceleration are similar to the state of the art

• Material models must be evaluated


Euro-NCAP polecrash


End of part 1








Index


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


Compression Tests on Polyurethane

Foams

Density 30 kg/m³ Density 300 kg/m³

After testing

High elastic behavior Brittle behavior


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


Global crippling Shear failure of core material Wrinkling

Sandwich Elements in In-plane

Load Case

Stand Februar 2013


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


• Box structure

• Cross structure

Application Examples

Tests on Structural Components

Stand Februar 2013








Index


Front Structure

General Information


Front Structure

Static Tests


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








Index


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 €


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!

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