(title of presentation – go to ‘slide master’ to put in)

Seven rules for lightweight design

Erik Tempelman, DeFabrique, 20.11.2012 Constructeursdag Out of the Box ontwerpen

Acknowledgements go to…

Richard van der Windt

Olatunji Ladojah

Paul Kengen

Ruben van der Laan

Bastiaan de Jong

Luc van den Heuvel

Fon-Wang Chan

Elena Ferrari

Tijn Huttenhuis

Erik Baas

Jeroen Vlek

Daan Tenwolde

Sander Nieuwveld

Thijs de Vries

Floor Baas

Barend Vermeulen

Bjorn-Evert van Eck

Veronie Croese

Lindy Hensen

Anke Kempen

Tom Schouten

Kim Rutten

Alexander Verhuizen

Sven Herberigs Paul van Adrichem

Ivo Roos

Marijn Hooghoudt

Nienke Veenendaal

Ruud van Gool

Marcel Bolten

Leonie van Andel

Arend-Jan van Lent

Niels van Velzen

Steven Buskermolen

Stephan Maaskant

Michiel Verhaar

Alexander Ettema

Arnold Dijkstra Antonio Recamier Elvira

Sander Homs

Tsu-Han Kuo

Ridzert Ingenegeren Joep Oberendorff Maarten Kamphuis

What it is…

Lightweight design is the science and the art of making things

as light as possible, always within constraints

Why lightweight design matters…

• Motor vehicles: better performance and/or lower fuel consumption

• Portables & wearables, bikes etc.: improved comfort

• Mass-produced products: reduced cost

But also: any product can

have a lower eco-impact

if it requires less material

Apart from all of that,

lightweight design is

challenging and fun

Courtesy NPSP and Maarten van Severen and Fabian Schwärzler for Pastoe

What it is…

Lightweight design is the science and the art of making things

as light as possible, always within constraints

products, structures

numbers, methods, predictions

choice, creativity, style

product constraints

process constraints

knowledge constraints

from pure tension… to pure compression

What it isn’t…

Taking a perfectly normal product and replacing the materials inside with ‘lightweight’ alternatives IS NOT lightweight design

results: - not very much lighter (usually) - not quite as functional (often) - much more expensive (always)

Rule # 1

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Clarence L. ‘Kelly’ Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule # 1: illustration

Rule # 2

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule # 2: illustration

Rule # 3

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule # 3: illustration Same force, different direction! Slender beam, with L/H = L/B = 10 What about stiffness? δtension = FL/(EA) with A = BH

δbending = FL3/(3EI) with I = BH3/12

And what about strength? σtension = F/A σbending = FL/W with W = BH2/6

Then σbending / σtension = 60 NB2: comparison gets even worse for torsion

NB1: for hollow beams (T/H = 10), the two ratios are ‘just’ 244 and 44

Then δbending / δtension = 400

solid square beam LxBxH

δ

δ

F

F

Rule #3: another illustration (1 of 3)

F

Rule #3: another illustration (2 of 3)

F

Rule #3: another illustration (3 of 3)

F

Rule # 4

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule # 4: illustration

aluminium

magnesium

GFRP/CFRP

extrusion (+)

roll-forming blanking, bending deep drawing die pressing

casting forging machining

extrusion (-)

(rare) casting (+)

forging (-) machining

pultrusion

thermoforming filament winding RTM, autoclaving

(rare)

(continuous fibres)

+/- denotes relative suitability

‘Ashby criterion’: 2√E/ρ 3 √E/ρ 1 √E/ρ

Rule # 4: another illustration

Kirk precision: cast magnesium frame Lotus: CFRP monocoque frame ‘standard’ aluminium frame

steel ‘tensegrity frame’ courtesy Frans de la Haye

Rule # 5

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than absolutely necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule #5: illustration

Rule #5: another illustration

load

deflection

Rule # 6

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than absolutely necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Rule # 6: illustration

Bone Chair (inspired by Klaus Matteck) courtesy Joris Laarman Lab

EADS: 3D printed plastic bike

Rule # 7

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than absolutely necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

Yield Strength, MPa

Stra

in-t

o-f

ailu

re, %

Yield Strength, MPa

interstitial-free

mild

interstitial-free, high strength

bake-hardening

chrome-manganese

high strength, low alloy

dual-phase

transformation-induced plasticity

martensitic

twinning-induced plasticity

Stra

in-t

o-f

ailu

re, %

Rule # 7: illustration

AW-6082 (T4-T6) Source: Praktijkboek Hoge Sterkte Staal, FDP

Summarizing…

• DO NOT over-specify “Let the mission design the plane, not the other way around” (Kelly Johnson)

• DO NOT use factors of ignorance instead, use factors of safety

• DO NOT allow bending and torsion … but if you have to, make optimal use of the available space

• DO NOT choose material, shape and production process independently instead, find the right combination

• DO NOT use more joints than absolutely necessary bonus: cost benefit

• DO NOT stop optimizing until it cannot possibly get any lighter “if the plane doesn’t fall from the sky it’s too heavy” (anonymous Boeing engineer)

• DO NOT rule out steel – not yet instead, discard your prejudice and see what’s really out there

PS: want one more rule?

Rule # 8: be inspired by Nature

Reference: “Lightweight Materials, Lightweight Design?” E. Tempelman, 2012, Delft University of Technology. To appear in: “Materials Experience: Contemporary Issues in Materials and Product Design”, Karana, Pedgley and Rognoli (Eds.), Elsevier, Sept. 2013