World Virtual Conference on Advanced

Research in Materials and Engineering

Application

22 – 26 SEPT 2014

NEW APPROACH FOR FABRICATION OF AUXETIC FOAM

AND DETERMINATION OF POISSON'S RATIO

Mozafar Shokri Rad and Zaini Ahmad

Universiti Teknologi Malaysia, Malaysia

1

Overview

� Research background

� Introduction to auxetic foam

� Fabrication of auxetic foam

� Experimental testing on auxetic foam

� Preliminary results

� Conclusion and outcomes

2

Research background

Impact force

Frontal structureSurvival space

P1P2

∆∆∆∆ ∆∆∆∆

P1 < P2

� Energy absorber – protect the structure under consideration due

to the adverse effect of impact

� Thin-walled structures and lightweight foam – excellent impact

energy absorbers and high energy absorption efficiency

Square Circular Frusta Hat-section Conical

4

Research background

� Combination (foam-filled thin-walled tubes) – enhance energy

absorbing capacity

Research background

� Auxetic material - a material with negative Poisson’s ratio

Introduction to

auxetic foam

Introduction to

auxetic foam

Auxetic foam

Natural:

Cancellous bones,

graphites, etc.

Man-made:

polyurethane

foam, etc.

� Auxetic foam has potential to

meet a lot of needs of industry

� Auxetic foam may provide

desirable mechanical

properties for various

applications

� Aerospace

� Automotive

� Biomedical

� Composite

� Military

� Textile industry

Auxetic

Material

High

energy

absorption

High

impact

absorption

High

fatigue

resistance

High

bending

resistance

High shear

modulus

Introduction to

auxetic foam

Introduction to

auxetic foam

Aerospace • Vanes for gas turbine engine

• Thermal protection

Automotive

• Bumper

Military

• Helmet

• knee pad

• protective gear

Open Cell

FoamPollyol

Isocyanate

Fabrication of auxetic foam

Fabrication of open-cell foam

� Auxeticity of material can only be obtained by using open-cell foam

� Fabrication of open-cell foam

Fabrication of auxetic foam

� Forming a cubic auxetic sample

Sizing Silicate Glue Plastic Cover

Fabrication of auxetic foam

Oil

∼∼∼∼ 20 – 50 bar Air

Cubic foam

specimens

� Pressure is applied sufficiently

Fabrication of auxetic foam

� Resizing – just after pressurized

� Moulding – to prevent foam

expansion

� Heating (oven) – just above the

softening temperature

� Cooling at room temperature

Temperature ∼∼∼∼ 170o

Duration ∼∼∼∼ 20 minutes

Fabrication of auxetic foam

� Verification of auxeticity behaviour

� Poisson’s ratio measurement using

high speed camera

� Auxeticity of the foam and amount of energy absorption are

determined by fabrication parameter:-

� Volumetric compression pressure

� Heating temperature

� Heating time

Uniaxial compression test

P

Fabrication of auxetic foam

Auxeticity = f(VP, ∆∆∆∆T, t)

Experimental testing

� Energy absorption capacity is

determined:-

� Falling weight system (Method 1)

� High speed camera (Method 2)

� Poisson’s ratio is measured using

a high speed camera

Experimental testing

� Method 1 – determine the energy absorption capacity

� Based Newton’s second law for the impactor

� � ��� � ���� � �

Experimental testing

� Method 2 – determine the

energy absorption capacity

� Calculation of acceleration

function

High speed camera

Velocity function

Displacement function

of impactor

Acceleration function

Derivation

Derivation

Preliminary results

� Effect of hydraulic pressure, heating time and heating temperature

on Poisson’s ratio

Preliminary results

Specimen

No.

Hydraulic

Pressure

(bar)

Heating time

(min)

Heating

temperature

(oC)

Poisson’s

ratio

1 10 30 140 0.18

2 10 20 140 0.21

3 20 30 150 -0.08

4 20 20 150 -0.06

5 30 30 160 -0.22

6 30 20 160 -0.26

7 40 30 170 -0.28

8 40 20 170 -0.31

� Additional test - indentation resistance test

Auxetic foam

Steel indenter

Preliminary results

15

Replacement of auxetic foam with negative Poisson’s ratio may be anticipated to be

beneficial solution that promotes an advantage in energy absorption

performance, thus enhancing level of safety in impact applications

Conclusion and Outcomes

Thank you

for your attention