auxetic polymeric materials: expanding materials and ...•cleanable/tuneable filters (bnfl) •...
TRANSCRIPT
Auxetic Polymeric Materials: Expanding Materials and Applications
Andy Alderson [email protected]
What are auxetics?
Poisson’s ratio:xy = -(y/x)
Auxetic Material: Material with a negative Poisson’s ratio
+ve xy
-ve xy
Am I in the right place?
The Poisson’s ratio scale
0 +0.5 -1
Cork
‘Typical’ materials
Rubber
a-cristobalite
Crystalline cellulose
Microporous polymers
Annulus fibrosus
Auxetic or ‘anti-rubber’ materials
Why are auxetics of interest?
• Usefulness of the novel property itself: – Counter-intuitive (‘opposite’) response
– High volume change
• A route to achieving unusual or extreme values of other material properties not easily achievable in conventional materials
Indentation resistance
Non-auxetic Auxetic
For isotropic materials:
and -1 < < +0.5
xE
H
21 • Auxetics: a route to enhancing other material properties, e.g.:
• Enhanced indentation resistance
• Enhanced fracture toughness
• Enhanced volumetric strain energy
dissipation (Uv)
• Enhanced shear modulus
• Ability to naturally adopt dome shape
when bent out of plane
E
U v6
21 2
212
r
ET
Curvature
Non-auxetic Auxetic
12
213KG
12
12
RR
Naturally-occurring auxetic biomaterials
• Increasing number of natural soft biological tissues reported to display auxetic behaviour o Cat skin
o Cow teat skin
o Bovine common carotid arteries
o Human achilles tendon
o Stem cells
o Early stage amphibian embryo tissue (gradient properties?)
o Human annulus fibrosis?
• Likely to have evolved for optimised specific functionality • Gradient structure and properties evident
(Chena & Brodland, Journal of the
Mechanical Behaviour of Biomedical
Materials 2 (2009) 494-501)
Auxetic cellular solids
Honeycombs
Re-entrant hexagon
LIGA auxetic honeycomb
structure - pore dimension ~
100mm
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C C
C C
C
C
C
C
C
C
C
C
C
C
C
Theoretical molecular structures -
pore dimension ~ 10Å
Femtosecond laser ablated
auxetic honeycomb structure -
pore dimension ~ 1mm
Star (connected Hoberman spheres analogy)
single ‘building block’
2 x 2 building block assembly
4 x 4 building block assembly
32 x 32 building block assembly
Rapid prototyped
auxetic honeycomb
structure - pore
dimension ~ 1cm
• A shape-changing (gradient) honeycomb – In-plane uniaxial loading – stress-induced shape change – Complex curvatures under out-of-plane bending
Auxetic cellular solids
Foams
• Cleanable/tuneable filters (BNFL)
• Anisotropic foams (QinetiQ)
• Large area flat and curved thin foams (Sara Lee Branded Apparel, Hanesbrands Inc & Auxetic Technologies Ltd)
• Detailed x-ray microtomography and modelling of structure-properties relationships (Univs of Manchester & Malta)
(A. Alderson et al, Phys. Stat. Sol. B 2007, 244 817.)
PCT Patent application, No. WO 99/22838
US Patent application, No. US 2003/0042176
PCT Pub. No. WO2007/052054,
US Patent Publication US2009119820
UK Patent Application No. 0821287.0
(S.A.McDonald et al, Phys. Stat. Sol. B, 248 (1) (2011) 45)
(S.McDonald et al, Script. Mater., 60 (2009) 232)
(Movie courtesy Sam McDonald, Univ. Manchester)
Impact testing: R60FR foam (Custom Foams),
2.27kg flat dropper, height = 0.1m
Unconverted (UC) Auxetic (0.7 LCR)
R60FR foam, 2.27kg flat dropper, height = 0.1m
Unconverted
Auxetic
R45 foam (Custom Foams), 2.09kg dome
dropper, 1mm PP shell, height = 0.1m
Unconverted Auxetic
Hemispherical dropper R45 foam
Unconverted
Auxetic
Auxetic microporous polymers
10 mm PTFE
PTFE Tape
• Auxetic effect observed in
expanded PTFE tape/ribbon
(Evans & Caddock, 1989)
• Auxetic effect arises due to
material microstructure
consisting of nodules and fibrils
• Batch processing route
(compaction, sintering &
extrusion) developed (K.
Alderson et al, 1992/6/8)
• Nodule-fibril microstructure
replicated in other microporous
polymers
• Auxetic cylinders of UHMWPE,
PP and nylon fabricated
A. Alderson & Evans, 1995/7
Veronda & Westmann, J. Biomechanics (1970)
Cat skin
In-plane
Thru’
thickness
Frohlich et al, J. Zool. Lond. (1994)
Veronda & Westmann, J. Biomechanics (1970)
Caddock & Evans, 1989
Ex-PTFE
Auxetic fibres and textiles
• Polypropylene fibres (Alderson
et al, 2002)
• Polyester fibres (Ravirala et al,
2005a)
• Polyamide fibres (Ravirala et
al, 2005a)
• Polypropylene films (Ravirala
et al, 2005b)
• Novel continuous melt extrusion process developed to
produce auxetic monfilaments and films
PP Film
PP Fibre
LAB-SCALE MELT EXTRUSION
University
PROCESS DEVELOPMENT & FIBRE DEMONSTRATORS
INCREASE RANGE OF POLYMERS
INDUSTRIAL-SCALE MELT EXTRUSION
APPLICATIONS
2 Ends x 2 Picks Woven
Fabric (Auxetic Monofilament)
1 x 1 Rib Knitted Fabric
(Auxetic Monofilament)
Fabrics incorporating Auxetic fibres
Non Woven Fabric (PP Non
Woven containing 40%
Auxetic Monofilament)
Naturally-occurring auxetic nanopolymers
Crystalline cellulose – Kraft cooked spruce
Experimental data
Tc [min]
Poisson’s ratios
zx
(before yield)
zx
(after yield)
120 -1.06±0.53 -0.98±0.46
150 -0.91±0.25 -1.00±0.25
180 -0.76±0.3 -0.86±0.25
210 -1.17±0.26 -1.05±0.26
240 -0.26±0.15 N/A
M. Peura, et al (2006),
Biomacromolecules, 7, 1521-1528
z x
z y
Molecular mechanics simulations on
cellulosic auxetic mechanism
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
-0.01 -0.005 0 0.005 0.01 0.015 0.02
z
ij
xy
yx
xz
zx
yz
zy
ij
Y. T Yao, PhD thesis (University of Bolton) 2010
0
5
10
15
20
25
-0.01 -0.005 0 0.005 0.01 0.015 0.02
z
|di| (o)
δ1
δ2
z (GPa)
C4-H...O2
d(D…A)
(Å)
2 2.491
1.5 2.491
1 2.491
0.5 2.491
0 2.491
-0.5 2.491
-1 2.491
-1.5 2.491
-2 2.491
• z (z) > 0
• x > 0 → zx < 0
• y < 0 → zy > 0
(a) Before rod rotation (b) After rod rotation
y
x
y
xx
b
a
d
b
a
b
a
d
b
a
Rigid spacers
Rigid rod
b
a
b
a
Rigid spacers
Rigid rod
Gradient auxetic
structures =
morphing wing
boxes
Auxetic composites = reduced
composite damage volume
for replacement
Auxetic
honeycombs =
curved nose cone
panels
Auxetic constituents in hybrid
adhesives = stiffer joints
‘Auxetic balancing’ = lightweight
composite structures through
reducing thermal distortion
1
MN
MX
XY
Z
-2.595
-2.062-1.529
-.996486-.463755
.068976.601707
1.1341.667
2.2
OCT 17 2007
15:29:59
NODAL SOLUTION
STEP=1
SUB =1
TIME=1
UZ (AVG)
RSYS=0
DMX =2.595
SMN =-2.595
SMX =2.2
1
MNMX
XY
Z
OCT 16 2007
13:56:32
NODAL SOLUTION
STEP=1
SUB =1
TIME=1
S1 (AVG)
Distorted (no auxetic)
No distortion (with auxetic)
Multifunctional auxetic
structures and systems =
vibration damping
Sector case study: Aerospace
US ARO
Sector case study: Healthcare
Auxetic foam pads will improve wearer
acceptance and compliance in hip protector
devices due to:
• improved comfort/fit (double curvature)
• enhanced energy absorption (impact
response)
• lower device weight and/or volume
Hip implants with auxetic mesh stems
provide
• improved match to bone mechanical
properties
• reduced ‘stress shielding’
• a compensation mechanism for
loosening of the stem over time -
extending device lifetime and time
between implant replacement operations
Deployable gradient
auxetic structures for
space creation and
organ retraction in
keyhole surgery
The 'smart bandage' concept delivers controlled drug release
from wound dressings in response to swelling of the wound
Gradient one-piece foams
mimic the concentric core-
sheath structure of the
natural intervertebral disc.
The auxetic sheath
reduces disc bulge under
compression to reduce
lower back pain
Acknowledgements • Prof Kim Alderson (The Open University)
• Dr Tom Allen (Sheffield Hallam University)
• Prof Subhash Anand (University of Bolton)
• Titus Augustine (CMFT)
• Dr Vicky Coenen (University of Bolton/Rolls-Royce)
• Dr James Corden (Trustech)
• Dr Phil Davies (University of Bolton)
• Prof Ken Evans (University of Exeter)
• Dr Leon Foster (Sheffield Hallam University)
• Trishan Hewage (Sheffield Hallam University)
• Dr Sam McDonald (University of Manchester)
• Dr Frank Nazare (University of Bolton)
• Dr Naveen Ravirala (University of Bolton)
• Dr Amit Rawal (Indian Institute of Technology)
• Mohammad Sanami (University of Bolton)
• Prof Fabrizio Scarpa (University of Bristol)
• Dignesh Shah (Sheffield Hallam University)
• Dr Ginny Simkins (University of Bolton)
• Jonathan Shepherd (Griffith University, Gold Coast, Australia)
• Dr Gill Smart (University of Bolton)
• Dr Muhammet Uzun (University of Bolton)
• Prof Phil Withers (University of Manchester)
• Dr Yong Tao Yao (Harbin Institute of Technology)