1

Aluminium as a structural material

An introduction

by

Professor Magnus Langseth

2

Contents

• SFI CASA

• Why aluminium as a structural material?

• Behaviour of aluminium alloys

• Constitutive and fracture modelling

• Component and system behaviour - validation

• Aluminium in the offshore industry

– Examples

3

Contents cont.

• Design guidelines

– Basis of design

– Materials

– Classification of cross-sections

– Local buckling resistance

– Heat affected zone

– Column buckling

• Simple design example

4

SFI CASA

Centre for Advanced Structural Analysis

2015-2023

5

Innovation in Norway

• A knowledge based NORWAY NORGE (Reve og Sasson, 2010)

– Four premises for future business life in Norway

• Product and processes have to meet the needs of the

customer

• The industry has to ensure that their products and processes

have a high level of knowledge

• The industry has to meet the international competition

• The industry has to be environmental robust, i.e. fulfil

environmental demands

6

Innovation in Norway

– One way to contribute to innovation in Norway is to

use «Advanced Structural Analyses»

• Increased competition by

– Smarter and more environmental friendly structures and

products

– Reduction of time of bringing a product to the market

– Reduction of cost

• Improved competition against nations that have lower labour cost

– Advanced Structural Analyses represents an

important element in risk management analysis

• Accidents, natural hazards, terrorist acts etc

7

Credibility

• Competence of the analysts conducting the work

• Quality of the physical modelling

• Verification and validation of models

• Uncertainty quantifications and sensitivity

analyses, i.e. accuracy of modelling and what is

“good enough”

8

9

10

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Industrail

Partners

Oil & Gas Physical

Security

Transportation

Equinor x

DNV-GL x

Multiconsult x x

KMD x

NSM x

NDEA x

NPRA x x

Hydro Aluminium x x x

Benteler Al Systems x

Audi x

Honda x

Toyota x

BMW x

Renault x

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Transportation Physical security Oil & Gas Fish farming

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Research strategy and programmes

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FractAlMicrostructure-based Modelling of Ductile Fracture in Aluminium Alloys

• Main objective

– To develop and validate a novel microstructure-based modelling framework for

ductile fracture in aluminium alloys and thus to introduce credible multi-scale

simulation in design of aluminium structures against failure

• Key numbers:

– Duration: 2016-2021 (5 years)

– 5 PhD candidates (5 x 3 years)

– 2 postdocs (2 + 4 years)

– Funding: approx. 30 MNOK

– Funding agencies:

• Research council of Norway (50%)

• NTNU (50%)

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Multi-scale

testing,

modelling and

simulation

ˆ ˆˆ e

ij ijkl klC D

ˆ ˆ ˆe p

ij ij ijD D D

ˆ ˆ( )ˆˆ

p

i

k

k

l

j

l

gD

Basic research Technology transfer

Ready to use technology

16

Numbers:

• Budget: NOK 292 000 000 • PhD candidates: 20• Post docs: 5• SINTEF: 3-4 man-years• Master’s: 160-200

Overview of CASA

17

Key professors/scientists

• Host institution NTNU

– Department of Structural Engineering• Professor Tore Børvik

• Professor Arild Holm Clausen

• Professor Odd Sture Hopperstad

• Professor Magnus Langseth

• Professor Aase Gavina Reyes

– Department of Physics• Professor Randi Holmestad

– Department of Materials Science and Engineering• Professor Knut Marthinsen

• Research partner

– SINTEF Materials and Chemistry• Dr Odd-Geir Lademo

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Why aluminium as a structural material?

19

The bad points about aluminium

• Cost– Material

• 50% weight reduction, aluminium=steel

• Effect of temperature– Aluminium weakens more quickly than steel

• Elastic modulus– Buckling

– Deflection

• HAZ– Softening at welds

– Localisation of strains

• Fatigue

• Thermal expansion– Expands and contracts twice as much as steel

20

The good points about aluminium

• Low weigtht (one third of steel)– Reduction of fuel consumption

– Lower carbon dioxide emission

• Extrusion process– Cross section geometry

• Recycling– Energy input equal to 5% of the energy needed to produce primary aluminium

• Low temperature performance

• Non-rusting– Unpainted

• Machinability and weldability

• Good energy absorbing capabilities– Increased specific energy compared to steel

21

Behaviour of aluminium alloys

22

Plastic anisotropy

24

AA6060-T4

Extrusion direction

200

220

240

260

280

300

0.001 0.01 0.1 1 10 100 1000 10000

Strain rate [s -1]

Flo

w s

tress s

_5

[MP

a]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Fra

ctu

re s

tra

in p

_f

s_5

p_f

25

Heat affected zones (HAZ)

AA6082-T6

26

Fracture modes

27

Constitutive and fracture modelling

Behaviour and modelling of joints

28

Model framework

Yield surface

Isotropic

hardening

Kinematic

hardening

Anisotropy/

texture

Disloc. density/

ageingDeform. induced

anisotropy

Flow rule

Viscous

stress

Damage &

Fracture

Plastic slip

(Schmid’s law)Rate effects/

PLC-effect

Microvoids/

microcracks

ˆˆ :σ C D

29

Behaviour and Failure of Flow Drill Screw Connections in Aluminium structures

FDS connection Process

Component

J.K. Sønstabø,HONDA/CASA, NTNU

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Main research achievements

• Virtual laboratory for design of aluminium structures

• Multiscale modelling framework for structural joints

Chemical composition

&

Thermal history Texture & microstructure Void & particle types Imperfection size

Nanostructure

modelling

Crystal plasticity

modelling

Unit cell

modelling

Localization

analysis

Continuum

modelling

Mesoscopic model Macroscopic model Structural analysis

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Crashbox bumper system

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Trolley

Bumper

Interface plate

Longitudinal

y

z

x

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The kicking machine

Photocells

Axial load

cells

Multi-reaction

load cell

Hydraulic piston

accumulator

Hydraulic/pneumatic

actuator

Trolley

Arm

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A

ASection A-A

Trolley

Load cell

Crash boxBumper

Top wall load cell

Bottom wall load cell

Load cells

Mx

My

Mx

My

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Test data

Crushing

Failure

Bending

Failure

Tear/Shear

Failure

Local

Buckle

36

Predictions

37

Aluminium in the offshore industry

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Living quarter

Helideck

Helideck

Telescopic gangway

Prefabricated walls

Stairtowers

Support for lifeboats

Use of aluminium offshore

Protection covers

Topside: Handrails, walkways,

stairs, flexibarrier etc.

39

Use of aluminium offshore

40

Design guidelines

41

Structural Eurocodes

• EN 1190 Eurocode 0: Basis of structural design

• EN 1991 Eurocode 1: Actions on structures

• EN 1992 Eurocode 2: Design of concrete structures

• EN 1993 Eurocode 3: Design of steel structures

• EN 1994 Eurocode 4: Design of composite steel and concrete structures

• EN 1995 Eurocode 5: Design of timber structures

• EN 1996 Eurocode 6: Design of masonary structures

• EN 1997 Eurocode 7: Geotechnical design

• EN 1998 Eurocode 8: Design of structures for eathquake resistance

• EN 1999 Eurocode 9: Design of aluminium structures

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Aluminium - Design guidelines

• EN 1999-1-1: Design of aluminium structures: General structural rules

• EN 1999-1-2: Design of Aluminium Structures: Structural fire design

• EN 1999-1-3: Design of Aluminium Structures: Structures susceptible to fatigue

• EN 1999-1-4: Design of Aluminium Structures: Cold-formed structural sheeting

• EN 1999-1-5: Design of Aluminium Structures: Shell structures

• BS 8118: Structural use of aluminium (1991)

• NORSOK Standard (1999)

– Reference is made to EC9

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EN 1999-1-1

• Part 1-1: General structural rules– Basis for design

– Materials

– Durability

– Structural analysis

– Ultimate limit states for members

– Serviceability limit states

– Design of joints

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45

Basis of design

46

Design process

Load: F

Characteristic value: Fk

Effect of load: Eγ

Design value: Fγ=γfFk

Material strength: f

Characteristic value: fk

Design value: fd=fk/γm

Design resistance: Rγ

Design check: Eγ<Rγ

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Materials

48

Modelling of the stress-strain curve

ep

e

0 0

ep e -

E

ep ee

e

E E

ep

e

0 0

ep e -

E

ep ee

e

E E

/e p pEe e e e

1( ) ,

m

pK mn

e

1

m

pK

e

n

E K

e

(Ramberg-Osgood equation)

(Power law)

49

50

Classification of cross-sections

51

b

t

52

53

54

55

0.000 0.001 0.002 0.003 0.004 0.005 0.006

Strain

0

25

50

75

100

125

150

Str

ess (

MP

a)

(a)(b)

(c)

(d)

(e)(f)

a) b) c)

d) e) f)

Local buckling of cruciform extrusion

6082-T6

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57

58

Local buckling resistance

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60

61

0.000 0.001 0.002 0.003 0.004 0.005 0.006

Strain

0

25

50

75

100

125

150

Str

ess (

MP

a)

(a)(b)

(c)

(d)

(e)(f)

a) b) c)

d) e) f)

Local buckling of cruciform extrusion

6082-T6

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63

Heat affected zone (HAZ)

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Heat affected zones (HAZ)

AA6082-T6

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66

67

68

Column buckling

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70

A

B

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Flexural buckling curves in EC9

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Design examples

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3 42450 10

TI Modified mm

Extrusion

75

Elevation

Section

Problem:The figure shows a walkway over a

stream. The two beams composing

the walkway have to be carried to

the construction site. Thus the

beams have to be lightweight and

an engineering firm has proposed

two steel beams IPE240. However,

the building owner wants also to

evaluate aluminium as a structural

material and has asked SIMLab at

NTNU to perform a calculation.

The design requirement is that the

two solutions shall have the same

deformation when subjected to

variable actions (loads). No

buckling(local or global) is

considered for the beams.

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Solution:

The deformation at midspan of a beam subjected to a uniform distributed load q is:

Thus

With

Then

45

384

qLW

EI

st st

al al st st al

al

E IE I E I and I

E

al stW W

6 438,9 10 / 3

st st alI mm and E E

6 4116,7 10

alI mm

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For a beam with a rectangular cross section:

Keeping the width constant gives:

Weight reduction of 52%

3112

I bh

133 1, 44

al st sth h h

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Concluding remarks

• Aluminium is a structural material for the future if it is used on its own premises, i.e. the design has to be based on the advantage of the material

• We need engineers who know the material and how it can be used in design. – Knowledge about how to use a design code is not sufficeint!

– Numerical simulations are a key tool in design

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Thank you for your attention!