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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
� 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
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
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
� 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
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