Journal of Mechanics Engineering and Automation 5 (2015) 427-434 doi: 10.17265/2159-5275/2015.08.001

Stainless Steel Composite Integrated in Modern Facade

Engineering

Marc Tulke1, Jennifer Watzke1, Michael Schomäcker1, Alexander Brosius1, Janine Bach2 and Helmut Hachul2

1. TU Dresden, Institute of Manufacturing Technology, Chair of Forming and Machining Processes, Dresden 01062, Germany

2. University of Applied Science and Arts Dortmund, Architecture and Metal Construction, Dortmund 44227, Germany

Abstract: This paper shows the results of characterising a stainless steel composite material for applications in facade engineering. A number of possible shapes generated with pneumatic stretch forming are presented as a result of simulation studies. In this context a model of a possible facade combined from different shapes is created to show the optical effect of the simulated shapes. Additionally, the manufacturing of a device for pneumatic stretch forming is discussed and first results of transforming the stainless steel composite material with pneumatic stretch forming are shown. Key words: Composite, design, facades, lightweight, pneumatic forming.

Abbreviation

PE polyethylene

PMS pneumatic stretch forming

1. Introduction

Due to characteristics like uncoated brightness and

a wide variety of surface patterning stainless steel is

often used for claddings [1]. Owing to the minimal

corrosion of stainless steel, the brightness of the steel

boards survives in an urban atmosphere. Other

properties like the weight, high material costs and

special demands on processing restrict the application

of stainless steel in facade engineering [2]. The

request for large sized steel boards with several form

elements and hidden fasteners in rear ventilated

claddings results in certain challenges, e.g., difficulties

in forming or high material costs and heavy boards

due to increasing material thickness. For optical and

ecological reasons stainless steel composites represent

an opportunity for application in claddings. The

composite consists of two thin and strong surface

layers and the thick and light core. The advantages of

composite materials include weight reduction

Corresponding author: Marc Tulke, Dipl.-Ing., research field:

forming processes. E-mail: marc.tulke@tu-dresden.de.

compared with solid material, acoustic and thermal

insulation, vibration damping and impact absorption

[3].

A composite with aluminium alloy as face material

and polyethylene as core is commonly used for

claddings. The aluminium composite is resistant to

corrosion and can be shaped liked sheet metal. It can

be formed by bending and folding with a surface

milling process [4]. These techniques enable

generating free formed shapes with sharp edges. The

stainless steel composite can be machined with same

techniques but with the unique design aspects of

stainless steel. Currently, free formed surfaces with

smooth transitions are favored in facade engineering

[5, 6]. A possible approach for visual upgrading of

facades is rear ventilated claddings. The composite

will be formed with PMS (pneumatic stretch forming).

This process allows the creation of individual surfaces

with soft curves. The characterization of the

composite material and the realization of the

pneumatic stretch forming take place within the

project: EVeFA—Stainless-Steel-Composite-Cladding.

The executing research centers are the University of

Technology Dresden and the University of Applied

Science and Arts Dortmund. Aim of the project is the

D DAVID PUBLISHING

428

application o

case study

Based on

orientations

arises across

2. Charact

The exam

thickness of

and made o

material ha

finish) and t

fire-retardan

polyethylene

To chara

material and

bulge test w

DIN EN IS

characteristi

primarily u

of the stainl

In tensile te

occur in the

that grow d

number of c

edge to th

Consequentl

beginning fr

properties o

layers are lis

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marked diff

curves and

fracture stra

is detected.

higher loads

The bulg

forming with

is clamped b

loaded with

blank holde

Sta

of stainless s

of possible

the light in

of the form

s the facade.

terisation

mined stainles

f 4 mm. The

f 1.4404. Th

s a bright a

the front side

nt core mate

e with a thick

acterise the

d the three s

were done. T

SO 6892 [7]

ic values an

used to desc

less steel com

est of the co

interlayer at

during the c

cracks increa

he middle o

ly, the face

rom the edge

of the compo

sted in Table

ng the propert

fference is r

the character

ain of the core

Therefore,

s in the compo

ge test is a

h a working

between the b

an oil pressu

er is 100 m

ainless Steel

steel composi

facades is s

ncidence an

m elements

ss steel comp

face material

he back side

annealed sur

e has a patter

erial is a pa

kness of 3.2 m

stainless

single layers

The tensile te

], is used to

d the flow

cribe the ma

mposite in si

omposite mat

an engineeri

course of the

ases. The crac

of the spec

e material

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osite materia

1.

ties of the tw

recognized. T

ristic values

e is about 5%

the core m

ound than as

preliminary

medium. The

blank holder a

ure. The inne

mm and the

Composite I

ites in facade

hown in Fig

nd the diffe

a different

osite board h

l is 0.4 mm t

of the compo

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article reinfo

mm.

steel compo

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aterial behav

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cimen (Fig.

delaminates

le specimen.

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The stress-st

are similar.

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material toler

single layer.

test for str

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and the die an

er diameter of

testing spee

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g. 1.

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Fig.

Tab

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Rp0

Rp0

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Rm/

Ag/

A /

r-va

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1.5

bulg

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high

bulg

bulg

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com

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imp

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0.05/ MPa 260

0.1/ MPa 273

0.2 / MPa 285

/ MPa 621

/ % 43

/ % 49.5

alue 0.66

value 0.22

mm/s. At th

ge of the com

m. The bulge

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mposite samp

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mposite board

print of the

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ade Engineer

dy of facade e

pecimen of the

ies of face mat

2R, patter

178

249

254

273

614

42.5

5 43.2

6 0.86

2 0.22

he time of th

mposite mate

of the singl

r and minor

presented in

f the composi

n the dome a

forming proc

the face m

le.

geometry of t

nt reflection

d. Especially

bead form e

bulge test p

ring

elements manu

composite.

terial, core, com

rned PE

18

1.4

2,4

4,0

13

3.5

5.0

-

-

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strain determ

Fig. 3. Fig.

ite after failur

and runs in a

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material is sim

the bulge in

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principal aes

ufactured with

mposite.

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39

61

63

65

129

29.7

37.8

0.36

0.1

height of the

hed about 38

about 33 mm

mined in the

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re. The crack

very straight

kling occurs.

milar to the

Fig. 4 itself

ight in one

ions and the

isual effects.

sthetical and

h

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8

m

e

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k

t

.

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f

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e

.

d

Fig. 3 Bulge

Fig. 4 Bulge

technologica

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engineering

and the cor

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when a cra

boards are

delamination

between the

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non-transfor

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transformed

fulfilled as s

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bulge tests

ack occurs.

cut into seg

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core and fac

ured roun

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recognisable

emand is the

site board th

boards in t

shown in Figs

ay the streng

t to the

acement diag

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ainless Steel

osite and face m

osite material.

on the compo

using the com

ond between

ansformed c

no delamina

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gments to ide

specimens n

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nd transitio

site board to t

e in this

e flat non tran

hat is neces

the facade. A

s.Fig. 4 and F

gth of the com

single she

gram is prese

at the tensi

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material.

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mposite in fac

the face mat

composite bo

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no disconnec

detected (Fig

on from

the form elem

figure. Ano

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Fig. 5.

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single sheet.

35 kN and th

out 4.97 kN.

Simulation

To estimate t

mposite mate

etch forming

t can be for

mufact. Form

de). To evalu

ults the bulge

merical and e

ained. For the

out 38 mm wh

ght is about

e difference c

core materi

mposite is tai

n-linear mater

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ade Engineer

lamination in

placement-diag

ore than twice

. The tensile

he tensile for

the formabil

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uate the reli

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33.6 mm fo

can be attribu

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rial behavior

des the prop

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force of the

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ity of the st

bination wit

mine potentia

rocess is sim

0 (regular m

iability of th

lated, too. Co

tests, simila

the height of

curs and in si

or the same m

uted to the ma

the material

ds metal. In

of the plastic

perties of th

429

terial.

he amount of

composite is

ngle sheet is

tainless steel

h pneumatic

al geometries

mulated with

mesh, implicit

he numerical

omparing the

ar results are

f the dome is

imulation the

major strain.

aterial law of

law for the

this case the

c interlayer is

he composite

9

f

s

s

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c

s

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430

material are

behaviour un

the plastic is

In the fo

shown. The

pneumatic s

of the air pr

changed wit

can be cre

necessary di

presented fo

The height

using no too

complex sha

maximum d

of about 54 m

The simul

used to iden

absorbed by

the pneuma

formability

process.

As part o

with respect

boards comp

this connect

(a

G

Fig. 7 Comp

Sta

determined i

nder biaxial s

s much differ

ollowing figu

e basic for

stretch formin

ressure in pr

th tool inserts

eated. The a

ie and option

orm elements

of the dome

ol insert (Fig

ape generate

dome height

mm.

lation of pneu

ntify the rea

y the device.

atic stretch

of the stainl

of simulation

t to the stiffn

pared with f

tion the disp

Displac

0 a) Stretch formi

Displac

0 (b) Stretch formGreen = die

posite boards f

ainless Steel

in tensile test

stress conditio

rent.

ure two pos

rm element

ng is a bulge

inciple is 1 m

s and in result

air pressure

nal tool inser

are shown ne

is about 120

g. 7a). Fig. 7

d with one t

of the two s

umatic stretc

action forces

Altogether, t

forming in

ess steel com

studies a po

ness of transfo

flat boards w

placement as

cement in mm

74 120 ng without tool

cement in mm

37 54 ming with tool

Black = tool

formed with PM

Composite I

t but the mat

on specificall

sible shapes

produced w

. The active

m2 which can

t different sh

is 6 bar.

rt to generate

ext to the sha

0 mm in cas

7b shows a m

tool insert an

ymmetric bu

h forming is

that have to

the simulatio

ndicates a g

mposite with

ossible advan

ormed compo

was examined

consequenc

l inserts

insert insert

MS.

ntegrated in

erial

ly of

are

with

area

n be

apes

The

e the

apes.

se of

more

nd a

ulges

also

o be

on of

good

this

ntage

osite

d. In

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Fig.

win

disp

to t

max

high

com

com

defo

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con

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give

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the

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alum

of

Modern Faca

Disp

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. 8 Displacem

nd equal to b

placement of

the wind ten

ximum displ

her stiffness

mposite board

mpletely elas

formation aft

mulated board

amined transf

cause of symm

played. For

ling factor of

Design Elem

A rear ventil

nstruction sys

described in D

ers of specif

uirements su

bility, natural

und insulation

e the build

nstructing eco

ates rear venti

Particularly a

building i

ailable. Comm

minium, copp

materials w

ade Engineer

lacement of tra

Displacement oinal state G

ment due to win

blasts near th

f the transform

ds to zero w

lacement of

is caused b

d. In both c

stic strain, so

fter the imp

ds have an

formed boar

metry only h

a better rec

f 3 is used to s

ments in A

ated facade

stem used for

DIN 18516 [8

fic materials

uch as separa

l lighting and

n (Fig. 9) and

ding a good

onomic and

ilated facades

variety of cl

ts unique

mon materials

per and zinc

with its char

ring

ansformed board

of flat board Green = deforme

nd load.

e coast is sim

med composi

while the flat

3.6 mm (Fi

by the geom

cases the de

o there is n

pact of the

area of 1

rd is shown

half of the cro

cognisability

show the disp

rchitecture

is a self-sup

r chamber fo

8]. It consists

in order to

ating inside f

d ventilation,

d last but not l

d look. Esp

sustainable h

s are first cho

adding eleme

look are co

s like steel, st

are applied.

racteristics a

d

ed state

mulated. The

ite board due

board has a

ig. 8). So a

metry of the

eformation is

no remaining

wind. The

m2 and the

in Fig. 7a.

oss section is

in Fig. 8a

placement.

e

pporting wall

orming which

s of different

meet several

from outside,

thermal and

least it has to

pecially, for

high-end real

oice.

ents that give

ommercially

tainless steel,

These range

and its own

e

e

a

a

e

s

g

e

e

.

s

a

l

h

t

l

,

d

o

r

l

e

y

,

e

n

Stainless Steel Composite Integrated in Modern Facade Engineering

431

Fig. 9 Concept of rear ventilated cladding.

surfaces are complemented by metal composite materials

like the new stainless steel composite material.

The simplest type of cladding elements are tailored

pieces of the stainless steel composite which can be

fitted to the supporting system by screwing, riveting

and bonding. A higher aesthetic value can be reached

by folding tailored pieces to tray panels and suspend

them into a special substructure.

Additionally to the possibilities described above the

composite material provide a big advantage. Easy and

complex folded shapes can be constructed by milling

the backside of the composite material. This milled

line causes a planned weakening of the composite

material, so that manufacturers are able to fold them

into panels by hand. In this way complex

three-dimensional figures can be easily and

economically produced (Fig. 10).

In contrast to the folding method which creates

sharp edged shapes, it is possible to create slightly and

soft curved cladding designs by using pneumatic

stretching. The following example shows the

visualisation of a possible design which is arranged as

a rear ventilated facade. The single composite board

of this example is already presented as result of

simulation in Fig. 7a.

The element describes a square facade element

whose centre bulges out smooth and gentle. Arranged

to a facade it could be associated with quilted fabrics.

The gleaming surface of the stainless steel composite

material emphasizes the variation of light and

shade which arises by its three-dimensional shape.

Fig. 10 Facade with folded shapes.

Fig. 11 Example facade 1.

The shown examples of facades demonstrate the

potential of the composite with regard to designing

facades. Especially, the different reflective properties

depend on the form elements in a surface.

5. Pneumatic Stretch Forming

Stretch forming describes the forming of metal

sheets while the material flow is suppressed due to the

clamped blanks [9]. In contrast to the stretch forming

with stiff stamps the pneumatic stretch forming uses

air pressure to transform the blank. Examinations on

sheet metal forming with working media were already

done during SPP 1098 with the aim of a homogeneous

material allocation for preforming deep drawing

shapes [10]. Due to lower elastic properties of the

composite material pneumatic stretch forming was

chosen to avoid delamination between the two

432

material com

real flow pro

to be determ

stretch form

The dema

claddings can

This forming

with smooth

elements. W

about 1 m2 c

be varied thr

tool, shown

forming wi

quality of th

with the too

without furt

steps. This

blanks alrea

As a res

forming pro

Based on th

1.2 × 1.2 m

about 1 m² a

The tool

The design

hydraulic pr

upper part b

Fig. 12 Mai

Fig. 13 Con

Sta

mponents as a

operties of th

mined. The ma

ming process i

and for new s

n be met with

g technology a

h transitions

With a pressur

can be transfo

rough tool in

n in Fig. 12

th pressurize

he parts, beca

ol. Therefore

ther surface

is limiting

dy have the s

sult of simul

ocess the form

he simulation

m2 and an acti

a tool is const

consists of a

is based o

ress to provi

uilds a herme

n principle of p

nstruction of pn

ainless Steel

a result of m

he combined c

ain principle

s shown in Fi

haping metho

h the pneumat

allows individ

between th

re up to 12 ba

ormed. The fo

nserts in the b

2. One majo

ed air is th

ause there is

, the parts c

treatment o

waste, beca

size needed fo

lating the pn

ming forces w

n results using

ive area of th

tructed, as sh

an upper and

on the use

ide the clamp

etical sealed s

pneumatic stre

neumatic stretc

Composite I

material flow.

components h

of the pneum

ig. 12.

ods for ventil

tic stretch form

dual round sh

e different f

ar large board

orm elements

bottom part of

or advantage

he intact sur

no direct con

an be assem

or added pro

ause the for

or the facade.

neumatic str

were determi

g a blank siz

he air pressur

own in Fig. 1

d lower tool p

of a 1,000

ping forces.

space to gene

etch forming.

ch forming too

ntegrated in

The

have

matic

lated

ming.

hapes

form

ds of

s can

f the

e of

rface

ntact

mbled

ocess

rmed

.

retch

ined.

ze of

re of

13.

part.

kN

The

erate

ol.

the

betw

bott

spa

form

tool

mod

com

form

stre

stre

exa

mou

forc

due

very

ligh

vari

redu

is n

cho

by

with

env

due

low

elem

D

vari

tool

6. E

B

of

pne

and

com

test

forc

boa

The

Modern Faca

air pressur

ween the upp

tom tool part

ce for the for

ming shapes

l inserts into

dules are va

mbined for ad

mability, the

etching of the

etch behavio

amined. For t

unted on the

ces on the bo

e to the size

y heavy if c

htweight des

iety of mater

uce weight. I

not subjected

osen to substi

over 50%. C

h the tool w

vironment. Ad

e to lower ma

wer part is m

ments are ma

Due to detai

iable tooling

l different sha

Experimen

Based on the

the new sta

eumatic stretc

d first tests ar

mposite descr

t the pressure

ce is about 5

ard is transfor

erefore, the r

ade Engineer

re for form

per and lowe

t stabilizes th

rmed compo

can be create

o the lower

ariable in for

dded variabil

e goal is to

e material. In

r different k

this purpose

e clamping s

ottom part of

needed for th

onventionally

sign offers t

rials in an in

In this case, f

to heavy load

itute steel, th

Consequently

will be much

dditionally, t

aterial prices

made of woo

ade of steel.

iled material

design could

apes of facade

ntal Procedu

numerical an

ainless steel

ch forming t

e done. For t

ribed in sectio

e is about 6

500 kN. The

rmed without

esult is a big

ring

ming the bla

er tool part (F

he forming a

site board. A

ed by insertin

part of the

rm and size

ity. In order

ensure a h

n an effort to

kinds of be

a modular be

surface of th

the tool are

he large blan

y made of st

the possibilit

ntelligent co

for the lower

ds, a beech tr

ereby reducin

y, handling a

h easier in

the tool costs

and machinin

d whereas o

studies a c

be investigat

elements can

ure

nd empirical e

composite m

the tool is m

the tests the s

on 0 is used.

bar and the

stainless ste

t the usage of

g bulge grow

ank clamped

Fig. 13). The

and creates a

A variation of

ng additional

tool. These

and can be

to maximize

homogeneous

optimize the

eads will be

ead holder is

he tool. The

very low but

nks it will be

teel. Modern

ty to use a

nstruction to

tool part that

ree wood was

ng its weight

and working

a laboratory

s are reduced

ng costs. The

only function

complex and

ted. With this

n be produced.

examinations

material and

manufactured

stainless steel

For the first

blank holder

el composite

f tool inserts.

wing from the

d

e

a

f

l

e

e

e

s

e

e

s

e

t

e

n

a

o

t

s

t

g

y

d

e

n

d

s

s

d

d

l

t

r

e

.

e

Stainless Steel Composite Integrated in Modern Facade Engineering

433

centre of the composite board. The composite board

before and after the pneumatic transformation still in

the tool is shown in Fig. 14.

The transformed composite board shows a smooth

transition from the non-transformed even part of the

blank to the bulge. Also the corners of the big bulge

have homogenous radii. The surface of the face

material shows no signs of tool contact and has kept a

bright metal surface as before the transformation. No

scratches or other defects can be detected in the range

of the die radius, either. The height of the bulge

reaches 113 mm in good accordance with the results

of the numerical tests that predicted a dome height of

120 mm. The resulting difference is only about 6%,

but with a small part of material flow that assists the

forming of the bulge. Therefore, the dome height will

be a little bit less when eliminating the material flow.

In Fig. 15, the effects of the different light incidences

across the shape are clearly visible and indicate the

new design possibilities. The two main prerequisites

for the application of the stainless steel composite

material in combination with pneumatic stretch

forming in facade engineering are the possibility to

fasten the boards to facades and prevention of

delamination during the forming. For that reason the

non-transformed part of the composite board needs to

remain flat. In the range of the beads the composite

board is flat and no delamination of the face material

exists.

When looking at the outer edges of the composite

board, however, a material flow from outside of the

beads can clearly be recognised. This material flow

needs to be suppressed because it can result in

wrinkles. Due to high wrinkling, the core material can

suffer cracks, because of its lower formability

compared to the face material. So the blank holder

force has to be increased to suppress the material flow

and to avoid wrinkling and realize a stretch forming

process.

(a) Composite board bevor the forming process

(b) Composite board after the forming process

Fig. 14 Composite board (a) before and (b) after pneumatic stretch forming without tool inserts.

(a) Front side (b) Back side

Fig. 15 Transformed stainless steel composite board.

7. Conclusions

The characterisation of the composite material shows

a good formability of the stainless steel composite

with pneumatic stretch forming. Comparing the tensile

test and the bulge test, the formability of the

composite depends on the stress condition. The results

of the simulation show that complex shapes can be

generated. In total the numerical and experimental

results indicate that the stainless steel composite

combined with the pneumatic stretch forming meet the

requirement of modern facade engineering and

designing. Shapes with soft curves and different

Stainless Steel Composite Integrated in Modern Facade Engineering

434

reflective properties in one surface can be created. No

delamination of the composite material occurs during

bulge test of the composite material. In pre-test of

pneumatic stretch forming only small areas at the

outer edges of the composite board display some

delamination effects. The compound of the whole

composite board survives even if the specimen fails in

bulge test or delaminates in very small parts of a 1 m2

big composite board. This property represents a

decisive factor for application in facade engineering.

8. Outlook

Additional tests of pneumatic stretch forming will

be done mainly with different tool inserts. In this way,

different shapes will be created and subsequently

investigated regarding their influence on the material

flow of the stainless steel composite. It is planned to

examine different geometries of beads and to

determine their influence on the material flow. Based

on these future results a mock-up will be produced for

presenting the possibilities of pneumatic

stretch-forming. Establishing the theoretical and

practical limits of this concept, a design catalogue

with different shapes will be compiled.

Acknowledgments

The presented results are based on the

investigations of the project

“EVeFA—Stainless-Steel-Composite-Cladding”,

which is kindly supported by the Research

Association for Steel Application (FOSTA).

References

[1] Euro Inox. 2005. Guide to Stainless Steel Finishes, 3rd

edition. Building Series, Volume 1.

[2] Hachul, H. 2013. Building Envelopes with Stainless Steel,

Stahl und Eisen, VerlagStahleisen GmbH Düsseldorf,

fourth ed., pp. 61-7.

[3] Zenkert, D. 1997. An Introduction to Sandwich

Construction, EMAS Publ.

[4] 3A Composites GmbH. 2014. ALUCOBOND,

Processing and Technical Data, 2nd edition.

[5] Franke, A. 2011. Vortrags-Campus: Neues Denken für

Nachhaltiges Bauen, Gebäudehüllen aus Stahl und Glas,

Internationale Projekte der Stahlarchitektur, Messe Bau.

(In German)

[6] Lother, K. 2013. Integrale Planung im Zusammenspiel

von Architekt und Fassadenbauer, DBZ, Fassade.

[7] DIN EN ISO 6892-1. 2009. Metallic

Materials—Tensile Testing, Method of Test at Room

Temperature.

[8] DIN 18516-1. 2010. Cladding for External Walls—Part 1:

Requirements, Principles of Testing.

[9] DIN 8585-2. 2003. Manufacturing Processes under

Tensile Conditions—Part 2: Stretch Reducing;

Classification, Subdivision, Terms and Definitions.

[10] Kleiner, M., Homberg, W., and Trompeter, M. 2006.

Hochdruckumformung einzelner Bleche,

Abschlussbericht zum DFG-Schwerpunktprogramm

SPP1098. (In German)