r critchley - materials that fight back

8/3/2019 R Critchley - Materials That Fight Back

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Materials that fight

backR. Critchley, I. Corni, K. Stokes, J. Wharton, F. Walsh, R. Wood

22 April 2010 TriboUK Imperial College London


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Outline

Current problems

Proposed solution

The outer hierarchical coating Inner auxetic foam

Where the project is heading

htt ://hermes52.deviantart.com/art/U-S-Arm -Soldier-34508852


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Body armour: problems and requirements

Lightweight (now the body armour is 13 kg)

Flexible wear and allowing mobility

Low cost

Stop projectile penetration

Diffuse the impact energy to reduce behind armour blunttrauma (BABT)

http://cn1.kaboodle.com/hi/img/2/0/0/c0/e/AAAAAhTx1z0AAAAAAMDr-A.jpg


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htt ://www.com uterweekl .com/PhotoGalleries/235075/757_30_Hi-tech-bod -armour.JPG

How it works

HybridSandwichStructure


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Outer layer: a laminate compositestructure to diffuse the energy of theimpact and to resist to deeperpenetrations

Armoursubstrate

Inner layer: auxetic foamstructure acting as small airbagsto protect the body from BABT

Schematic structure

1mm

5 mm

10 mm


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Outer hierarchicalcoating


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The outer hierarchical coating

It is well-known that biological materials present optimized structure andexcellent mechanical properties.

The challenge is to deposit a hierarchical hard and tough ceramic-metal

multilayered coating that mimics nature (e.g. nacre (mother of pearl),mollusc shell and ancient fish armour).

The initial coatings have been deposited by CVD (W3C and B13C2) andPVD (Ti-V-Zr and Ti-V-Zr nitride):

CVD is a high temperature process (1000C for B13C2) and thereforejust few substrate are compatible.

PVD coatings can be deposited on CVD films but the opposite is notalways true e.g. we experienced decomposition of the PVD filmsin the atmosphere needed for CVD deposition.


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Nacre (mother of pearl)

Nacre is a ceramic laminate composite made of aragonite tablet layersseparated by thin layers of an organic material (polymer).

Nacre resists impact by dissipating the impact energy through nano andmicron cracks, plastic deformation and elastic responses.

Barthelat, et al. Experimental Mechanics 2007

Materials Research to Meet 21st Century Defence Needs, 2003.


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Vent gastropod shell

Ortiz et al. PNAS 2010.

The hardness and Young modulus reported to be higher in the twoexternal layers (with the inner layer presenting the higher value) and lowerin the middle layer (ML).

The outer layer (OL) behaves as a sacrificial layer and helps to dissipatethe impact energy through localized micro-cracking and delamination.


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Ancient fish armour

Each layer had a specific deformation and energy dissipation mechanism:

The stiff outer layer transferred the energy of an applied load to the layersbelow

The stratified isopedine layer hinders deeper penetrations and preventscatastrophic cracking through micro-cracking in the sub-layers.

Bruet et al.Nature

Materials,2008.

Young modulus andhardness increase(inside to outside ofthe armour)


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Improved ballistic performanceof coated plates

Ozsahin and Tolun, Materials & Design 2010; Ozsahin and Tolun, Materials & Design, In Press.

zsahin and Tolun studied the ballistic performance against a highvelocity (> 350 m/s) impact 9 mm bullet of aluminium alloy plates with andwithout 0.762 mm thick cobalt-molybdenum-chromium or Zirconia plasmaspray coatings.

Penetration depth on the front face of the plate and the bulging on the

rear face of the plate were compared for plates with and without coatings.

The coatings improved theballistic resistance of the plateswith an increase in non-perforating projectile velocityand a decrease in penetrationdepth and bulging.


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Inner auxetic

foam


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Auxetic Materials What are they ?

Conventional materials have a positive Poissons ratio

Auxetic materials have a negative Poissons ratio - grow fatterwhen stretched

Evans and Alderson, Advanced Materials, 2000.

Poissons Ratio = _Change in X

Change in Y


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Auxetic Materials - Background

Auxetic materials have been known for approximately 100years

Field only started to be studied in 1987 by Rod Lakes

The term auxetic was coined by Ken Evans - derived fromthe Greek word auxetikos which means that tends toincrease

Surge in interest since the late1980s

htt ://www.imeche.or /NR/rdonl res/4CB11B44-DB9A-44D0-B94C-662AE7A93740/517/meshauxeticfoam94. n


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Auxetic Materials How they work

Fabricated through a compression, heating and coolingprocess

Foam cell structure determines the overall properties

Conventional Cell Structure Auxetic Random Rib Structure

Evans and Alderson, Advanced Materials, 2000.

x25x10


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Conventional Foam AuxeticFoam

x5 x5

Alicona InfiniteFocus

optical 3D measurement device


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Scanning Electron Microscopy (SEM)


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Testing Methods Indentation test

Falling drop impact test

High energy particleerosion test (350 m/s)

Ballistic test

Other Testing Methods: Compressive test

Tensile test

Shear test

3 point bending test Quasi-static cyclic loading

htt ://www.m mtechnolo ies.com/ima es/Batter Im actTest_med.http://english.ymhiten.com.tw/image/E-003a.jpghttp://www.worldoftest.com/img/products/Q250.jpg

http://www.tc.umn.edu/~seong001/web%20image/7R009r1.jpg

Increasei

n

strainr

a

te


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Where project is heading

Select a standard polymer foam most likely polyurethane

Determine optimum conditions for the selected foam

Characterise the foam

Test the foam in a numberof different situations

htt ://reasonsoflife.files.word ress.com/2008/08/success2. n ?w=317&h=320


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Acknowledgements

The author would liketo acknowledgeEPSRC and DSTL forproviding funding andopportunity for thisproject, and my projectsupervisors for all theirdirection and support.


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THE END

Any Questions ?

htt ://croak .deviantart.com/art/Universal-Soldier-19082158


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Understanding the threat - Bullets

r critchley - materials that fight back

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