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Materials that fight back

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Presentation on theme: "Materials that fight back"— Presentation transcript:

1 Materials that fight back
R. Critchley, I. Corni, K. Stokes, J. Wharton, F. Walsh, R. Wood Please use the dd month yyyy format for the date for example 11 January The main title can be one or two lines long. 22 April 2010 – TriboUK – Imperial College London

2 Outline Current problems Proposed solution
The outer hierarchical coating Inner auxetic foam Where the project is heading

3 Outline EPSRC and DSTL call:
Study the properties of new materials under high rate dynamic loading to enhance their damage tolerance. Proposals from the following areas: Nanomaterials or novel materials approaches to improve the resistance of materials to high rate mechanical loading, wear and impact. Modelling of the response of materials to high rate loading, including high rate materials property development for the input to such models. Predicting and improving the high rate deformation performance of polymer composite materials and structures. Novel ceramic materials, composite materials and steels- highlighted in the recent Defence Technology Strategy - that address these issues. Bio-inspired approaches to improving high rate materials response. The development of new techniques and the use of existing ones are both of interest.

4 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 blunt trauma (BABT)

5 Hybrid Sandwich Structure
How it works Hybrid Sandwich Structure

6 Schematic structure Armour substrate
Outer layer: a laminate composite structure to diffuse the energy of the impact and to resist to deeper penetrations 1mm Armour substrate 5 mm Discuss how the energy will be disipated. Bullet hits outer layer, where bullet fragmentation occurs, causing the coating and substrate to become destroyed (Intentional deformations thoughout layers to ensure, one layer destruction does not directly affect the others). Energy ‘punch’ travels through the material. Foam layer attempts to dissipate the energy across the whole body, opposed to a localised pressure. 10 mm Inner layer: auxetic foam structure acting as small airbags to protect the body from BABT

7 Outer hierarchical coating
Use divider pages to break up your presentation into logical secti

8 The outer hierarchical coating
It is well-known that biological materials present optimized structure and excellent 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) and PVD (Ti-V-Zr and Ti-V-Zr nitride): CVD is a high temperature process (1000ºC for B13C2) and therefore just few substrate are compatible. PVD coatings can be deposited on CVD films but the opposite is not always true – e.g. we experienced decomposition of the PVD films in the atmosphere needed for CVD deposition. 8

9 Nacre (mother of pearl)
Barthelat, et al. Experimental Mechanics 2007 Materials Research to Meet 21st Century Defence Needs, 2003. Nacre is a ceramic laminate composite made of aragonite tablet layers separated by thin layers of an organic material (polymer). Nacre resists impact by dissipating the impact energy through nano and micron cracks, plastic deformation and elastic responses.

10 Vent gastropod shell Ortiz et al. PNAS 2010. The hardness and Young modulus reported to be higher in the two external layers (with the inner layer presenting the higher value) and lower in the middle layer (ML). The outer layer (OL) behaves as a sacrificial layer and helps to dissipate the impact energy through localized micro-cracking and delamination.

11 Bruet et al. Nature Materials, 2008.
Ancient fish armour Bruet et al. Nature Materials, 2008. Young modulus and hardness increase (inside to outside of the armour) Each layer had a specific deformation and energy dissipation mechanism: The stiff outer layer transferred the energy of an applied load to the layers below The stratified isopedine layer hinders deeper penetrations and prevents catastrophic cracking through micro-cracking in the sub-layers.

12 Improved ballistic performance of coated plates
Özsahin and Tolun studied the ballistic performance against a high velocity (> 350 m/s) impact 9 mm bullet of aluminium alloy plates with and without mm thick cobalt-molybdenum-chromium or Zirconia plasma spray 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 the ballistic resistance of the plates with an increase in non-perforating projectile velocity and a decrease in penetration depth and bulging. Ozsahin and Tolun, Materials & Design 2010; Ozsahin and Tolun, Materials & Design, In Press.

13 Inner auxetic foam Use divider pages to break up your presentation into logical sections and to provide a visual break for the viewer. The title can be one or two lines long.

14 Auxetic Materials – What are they ?
Conventional materials have a positive Poisson’s ratio Auxetic materials have a negative Poisson’s ratio - grow fatter when stretched Poisson’s Ratio = _ Change in X Change in Y Evans and Alderson, Advanced Materials, 2000.

15 Auxetic Materials - Background
Auxetic materials have been known for approximately 100 years Field only started to be studied in 1987 by Rod Lakes The term auxetic was coined by Ken Evans - derived from the Greek word auxetikos which means ‘that tends to increase’ Surge in interest since the late 1980’s

16 Auxetic Materials – How they work
Fabricated through a compression, heating and cooling process Foam cell structure determines the overall properties x10 x25 Conventional Cell Structure Auxetic Random Rib Structure Evans and Alderson, Advanced Materials, 2000.

17 Alicona InfiniteFocus optical 3D measurement device
x5 x5 Conventional Foam Auxetic Foam

18 Scanning Electron Microscopy (SEM)

19 Auxetic Materials – Importance to the high strain project
Non-auxetic Auxetic foam to act as ‘smart airbags’ Act behind sandwich structure Auxetic materials are popular for their increase in impact resistance and energy absorption: - Reduce BABT - Reduce / prevent backface signature injury Auxetic Evans and Alderson, Advanced Materials, 2000.

20 Increase in strain rate
Testing Methods Indentation test Falling drop impact test High energy particle erosion test (350 m/s) Ballistic test Other Testing Methods: Compressive test Tensile test Shear test 3 point bending test Quasi-static cyclic loading Increase in strain rate

21 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 number of different situations

22 Acknowledgements The author would like to acknowledge EPSRC and DSTL for providing funding and opportunity for this project, and my project supervisors for all their direction and support.

23 THE END Any Questions ?


25 Understanding the threat - Bullets

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