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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
11
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
12
Transportation Physical security Oil & Gas Fish farming
13
Research strategy and programmes
14
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%)
15
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
18
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
30
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
31
Crashbox bumper system
32
Trolley
Bumper
Interface plate
Longitudinal
y
z
x
33
The kicking machine
Photocells
Axial load
cells
Multi-reaction
load cell
Hydraulic piston
accumulator
Hydraulic/pneumatic
actuator
Trolley
Arm
34
A
ASection A-A
Trolley
Load cell
Crash boxBumper
Top wall load cell
Bottom wall load cell
Load cells
Mx
My
Mx
My
35
Test data
Crushing
Failure
Bending
Failure
Tear/Shear
Failure
Local
Buckle
36
Predictions
37
Aluminium in the offshore industry
38
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
42
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
43
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
44
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
47
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
56
57
58
Local buckling resistance
59
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
62
63
Heat affected zone (HAZ)
64
Heat affected zones (HAZ)
AA6082-T6
65
66
67
68
Column buckling
69
70
A
B
71
Flexural buckling curves in EC9
72
73
Design examples
74
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.
76
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
77
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
78
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
79
Thank you for your attention!