Sacha Cavelier & Francois Barthelat (supervisor) McGill University, Department of Mechanical Engineering, Biomimetic lab

sacha.cavelier@mail.mcgill.ca, francois.barthelat@mcgill.ca

Conclusions

• Nacre (or mother-of-pearl) from mollusk shell is made of millions of microscopic mineral tablets assembled in a 3D brick wall structure. Nacre is so well constructed that it is 3000 tougher than the mineral of which it is made.

• Urethane glue shows good start of sliding but elasticity is not enough to let tablets slide completely. • PDMS allows sliding but locking is rare so strength does not increase a lot. • Repositionable glue 3M is too strong and the tablets break before any sliding and locking. • Repositionable glue Easy Tack has a strength low enough to let sliding and locking appear. It clearly increases the strength, proving that the nacre structure can improve mechanical properties of materials. • This phenomenon also exists when instead of glue a pressure is applied like in a house wall.

A bio-inspired construction spreads damage and dissipates energy, leading to more stable and progressive failure

Locking phenomenon due to the dovetail

• Masonry construction mimicking nacre may display superior toughness, damage tolerance and robustness in extreme loading conditions such as earthquakes.

• In this research we develop and test a clay brick wall bonded by different types of glue, with a structure directly bio-inspired by nacre.

Goal • Design and fabricate small-scale bio-inspired “brick

walls” made of brittle clay to demonstrate the potential of bio-inspired construction.

Motivation

Towards bioinspired housing : Stronger brick walls inspired from seashells

References: - F. Barthelat, R. Rabiei, Journal of the Mechanics and Physics of Solids 2011, 59, 829-840. - F. Barthelat, D. J. Zhu, Journal of Materials Research 2011, 26, 1203-1215. - H. J. Gao, International Journal of Fracture 2006, 138, 101-137. - L. J. Bonderer, A. R. Studart, L. J. Gauckler, Science 2008, 319, 1069-1073. - ASTM, ASTM International 2008. - R. Rabiei, S. Bekah, F. Barthelat, Acta Biomaterialia 2010, 6, 4081-4089.

Acknowledgments: Barthelat group – Ahmad Khayer, Mohammad Mirkhalaf, Elton Tan and Francois Barthelat - facilities, training, interpretation, support

Nacre from mollusk shells is one of the toughest hard biological materials known. Here we show that that we can “steal” design concepts from nacre to build masonry with superior properties

Brick wall (+Easy TackTM)

Sample fabrication

• The maximal force and the dimensions of the sample give the maximal strength.

Strength of individual bricks • To measure the strength of individual bricks, sample is mount on the

Fullam machine and a tensile force is applied until sample breaks. Carbon fibers are used to fix the sample.

Results of tensile test

• The maximal force and the dimensionsof the sample give the maximalstrength.

• To measure the strength of individual bricks, sample is mount on theFullam machine and a tensile force is applied until sample breaks.C bCarbon fibfibers are dused to fifix hthe samples .

Results of tensile test

The Fullam machine.

Testing protocol Maximal strength : 8,86+/-3,44 MPa

• Same tensile tests than for simple bricks are performed on rectangular and dovetail brick walls for each glue.

• Urethane has been tested because of the elasticity of this glue.

Clay brick Adhesive

Two different brick walls

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 0.1 0.2 0.3 Strain

Stre

ss (M

Pa)

Stress – Strain curve

Locking clearly

observed on pictures and

curves.

No locking

Dovetail

Rectangular

0

0.05

0.1

0.15

0.2

0.25

0 0.1 0.2 0.3 0.4Strain

Stre

ss (M

Pa)

No difference between

dovetail and rectangular

shape.

3M too strong and tablets beak. No

locking. Dovetail

Rectangular

Max stress (Kpa) Locking Rect. 200 Dov. 170 No

Mini vice Teflon plate1

Brick wall Piece of steel2

Carbon fibre Teflon plate1

Foam3

Metallic plate Metallic plate

Screw

1 : To minimize friction forces. 2 : Sticked on the wall, to assure uniform pulling. 3 : To apply uniform pressure (foam property). The mini-vice

• In real brick wall, mortar is brittle. After it breaks, only friction between the bricks and gravity of the house ensures adhesion of the bricks in shear. In this experiment, a mini-vice applies pressure on a brick wall without glue.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.01 0.02 0.03 0.04 0.05 0.06Strain

Stre

ss (M

pa)

Results

Tablets break: even if tablets are breaking, the strength increases

After a while instead of decreasing, the strength is in a plateau, probably due to the locking of the dovetail bricks

• A foam is used to apply a uniform pressure. Its properties allow to keep a constant pressure and so simulate the gravity (like in a house wall).

• So the mini-vice reproduce house wall with a mortar broken.

• The natural phenomenon of locking existing In nacre is reproducible experimentally and it increase the material strength.

• Repositionable glues with low strength are the best glues offering combination of large deformation in shear (to dissipate energy) and low strength ( to avoid fracture of the bricks).

The natural phenomenon of locking existing In nacre is reproducibleexperimentally and it increase the material strength.

• Repositionable glues with low strength are the best glues offeringcombination of large deformation in shear (to dissipate energy) and lowstrenggth (( to avoid fracture of the bricks)).

MAIN FINDINGS :

Standard house wall: a single cracks leads to catastrophic failure

Structure of nacre. • The micro-bricks in nacre are

not flat but wavy, which generates strain hardening, prevents localization of damage and enhances overall energy absorption.

•••••••••••••••••••• SSSSame tttensiiiilllle tttesttts ttthhhhan ffffor siiiimplllle bbbbriiiickkkks are

performed on rectangular and dovetail brickwalls for each glue.

•••••• Urethane has been tested because of theelasticity of this glue.

Brick wall (+urethane)

Brick wall (+PDMS)

Max stress (Kpa) Locking

Rect. 26

Dov. 46 Yes

Brick wall (+3MTM)

Views of wall

Results

0

0.05

0.1

0.15

0.2

0.25

0 0.1 0.2 0.3 0.4Strain

Stre

ss (M

Pa)

No differencebetween

dovetail and rectangular

shape.

3M too strong and tablets beak. No

locking. Dovetail

Rectangular

Max stress (Kpa) LockingRect. 200Dov. 170 No

Brick wall (no glue)

Views of wall

Results

Stress – Strain curve

• PDMS is a polymer whose strength can be controlled thanks to the amount of crosslinker (6.9, 14.7 or 30% tested) .

• Easy Tack has been tested because of the repositionable property of this glue.

• The low strength allows sliding and locking of the tablets.

• 3M has been tested because of the repositionable property of this glue and the high strength.

• But its high strength does not allow any locking (tablets break before).

• 1. Clay plates shaped in a Teflon mould.

• 2. High temperature treatment at 1000 C.

• 3. Plates cut accurately with a diamond saw.

• 4. Assemble the tablets with glue in order to build a brick wall.

• 5. Tensile tests on the Fullam machine. This loading machine measures forces and displacement while tensile forces are transmitted to the sample.

The diamond saw

• Two types of natural clay brick wall (rectangular and dovetail) are designed and the fabrication is the following :

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.00E+00 5.00E-02 1.00E-01 1.50E-01Strain

Stre

ss (M

Pa)

Both sliding and

breaking observed. So locking is also

obervable.

Views of wallStress – Strain curve

Both sliding and breaking.

Max stress (Mpa)

Locking

Rect. 1,08 Dov. 1,25 Sparsely

• Results show that tablets slide but also break due to the strength of the glue.

Results

0

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15

Dov. 6.9%Dov. 14.7%Dov. 30%

Strain

0

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15

Rect. 6.9%Rect. 14.7%Rect. 30%

Strain

Stre

ss (M

Pa)

S

tress

(MP

a)

Max stress (Kpa)

Locking

Rect. 6.9% 100 Rect. 14.7% 190 Rect. 30% 150 Dov. 6.9% 120 Sparsely Dov. 14.7% 220 Sparsely Dov. 30% 170 Sparsely

Sliding observable but locking is rare.

So strength is sparsely

increased.

14.7% seems to be the best crosslinker

amount. Views and curves Results