ballistic body armour using shear thickening fluids for enhancing stab resistance

81 Pages·2016·2.49 MB·English

by  Yan Wang

BALLISTIC BODY ARMOUR USING
SHEAR THICKENING FLUIDS
FOR ENHANCING STAB RESISTANCE

A Thesis submitted to the University of Manchester for the degree of Master of
Philosophy in the Faculty of Science & Engineering.

2016

Yan Wang
Textile Science & Technology
School of Materials
Contents
Abstract ................................................................................................................................................... 3
Lay Abstract............................................................................................................................................. 4
Declaration .............................................................................................................................................. 5
Copyright Statement ............................................................................................................................... 6
Acknowledgements ................................................................................................................................. 7
Chapter 1: Introduction .......................................................................................................................... 8
1.1. Background of the Research: the Necessity for Stab resistance ..................................... 8
1.2. The Problems: Difference between Stab resistance and ballistic resistance ........................... 9
1.3. Research Aim and Objectives ................................................................................................. 11
Chapter 2: Literature Review ................................................................................................................ 12
2.1. Materials used for Body Armour............................................................................................ 12
2.2. Approaches to Improve the Stab resistance of Ballistic Body Armour .................................. 14
2.3. Newtonian Fluid and non-Newtonian Fluid ........................................................................... 17
2.4. Classification of non-Newtonian Fluid ................................................................................... 17
2.5. Composition of Shear Thickening Fluids ................................................................................ 18
2.6. Theory of Shear Thickening Fluids ......................................................................................... 18
2.7. Factors Influencing Rheological Properties of Shear Thickening Fluids ................................. 20
2.8. Application of STF on Body Armour ....................................................................................... 22
Chapter 3: Experimental Methods ........................................................................................................ 25
3.1. Preparation of Shear Thickening Fluids ................................................................................. 25
3.1.1. Experimental Materials ............................................................................................... 25
3.1.2. Shear Thickening Fluids Production ............................................................................ 26
3.2. Rheology Test of the Produced STFs ...................................................................................... 27
3.3. Preparation of STF-impregnated Fabrics ............................................................................... 28
3.4. Stabbing Tests of the STF-impregnated Fabrics ..................................................................... 30
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Chapter 4: Results and Discussion ........................................................................................................ 33
4.1. Fraction of Weight and Volume of STFs ................................................................................. 33
4.2. Rheological Data and Analysis ............................................................................................... 34
4.2.1. Particle Size and Shear Thickening at Ambient Temperature ..................................... 34
4.2.2. Particle Weight Fraction and Shear Thickening at Ambient Temperature ................. 37
4.2.3. Dispersing Medium and Shear Thickening at Ambient Temperature......................... 40
4.2.4. Particle Size and Shear Thickening at Different Temperatures .................................. 43
4.2.5. Particle Weight Fraction and Shear Thickening at Different Temperatures ............... 48
4.2.6. Dispersing Medium and Shear Thickening at Different Temperatures ...................... 53
4.3. Specification of the STF-impregnated Fabrics ....................................................................... 58
4.3.1. Thickness of the STF-fabrics ........................................................................................ 58
4.3.2. SEM Pictures of the STF-impregnated Fabrics and Untreated Fabrics ....................... 61
4.4. Stabbing Tests Results and Discussions ................................................................................. 62
4.4.1. Particle Sizes and Performance of the STF-fabrics ...................................................... 62
4.4.2. Particle Weight Fractions and Performance of the STF-fabrics .................................. 66
4.4.3. Dispersing Media and Performance of the STF-fabrics............................................... 70
Chapter 5: Conclusions ......................................................................................................................... 74
Future Work .......................................................................................................................................... 76
References ............................................................................................................................................ 77
Appendix A: The structure of the Rheometer....................................................................................... 79
Appendix B: Engineered Knife Impactor ............................................................................................... 80
Appendix C: Composites of Backing Materials ..................................................................................... 80

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Abstract

The University of Manchester
Yan Wang
Master of Philosophy
Ballistic Body Armour Using Shear Thickening Fluid for Enhancing Stab Resistance
December 21st, 2016

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Lay Abstract
The improvement in stab resistance of ballistic fabric resulting from impregnating shear
thickening fluid into ballistic fabrics has been proved by a large number of researchers.
However, the performance of shear thickening fluid, particularly the critical shear rate,
can be affected by various factors. This thesis studies three production factors including
the size of dispersing particles, the particle weight fraction and the molecular weight of
the dispersing medium. Besides these three factors, the temperature has also been
studied as an environmental factor.
It was found that the shear thickening fluid (STF) with smaller particle size promotes
higher critical shear rate while the one with larger particle size leads to lower critical
shear rate. For the STFs made from the same particle size and dispersing medium, the
lower the particle weight fraction is, the higher the critical shear rate will be. The STF
made with lower molecular weight dispersing medium results in higher critical shear
rate, while the one with higher molecular weight dispersing medium results in lower
critical shear rate. The increase of temperature causes the shear thickening
phenomenon to occur latter while a decreased temperature leads to earlier occurrence
of shear thickening. In addition, the viscosities of the STFs decline with the increase of
temperature.
Under the condition of room temperature (20˚C), the performance of STF-impregnated
fabrics was tested by the drop tower test. The higher energy absorption can be achieved
by the STFs with a larger particle size, higher particle weight fraction, and higher
molecular weight of dispersing medium. It is notable that distinct improvement of the
energy absorption is offered by fully impregnating the fabric.
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Declaration

No portion of the work referred to in the thesis has been submitted in support of an
application for another degree or qualification of this or any other university or other
institute of learning.

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Copyright Statement

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owns certain copyright or related right in it (the ‘Copyright’) and s/he has given The
University of Manchester certain rights to use such Copyright, including for
administrative purpose.
2) Copies of this thesis, either in full or in extracts and whether in hard or electronic
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IP Policy (see http://documents.manchester.ac.uk/display.aspx?DoclD=24420), in any
relevant Thesis restriction declarations deposited in the University Library, The
University Library’s regulations ( see
http://www.library.manchester.ac.uk/about/regulations/) and in The University’s
policy on Presentation of Theses.

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Acknowledgements
I am grateful to Dr Xiaogang Chen, the supervisor of my MPhil study. He gave the
comprehensive advices to my project and guided me to carry out my project
systematically and sufficiently.
The second person I want to appreciate is Miss Yue Xu, a PhD student in Dr Chen’s
research group for providing guidance on the preparation of the experimental
materials, and for offering training on the use of the testing machine. Her discussions
with me on technical issues inspired me on analysis of experimental data.
Mr Basile Khara, the technician in Rheology Test Lab, is the third person I want to thank,
for providing training to me on the use of the rheometer and giving me some valuable
suggestions on testing my samples.
Lastly, I want to thank Mr Phillip Cohen and Mr David Kenyon, the technicians in the
Dye House for their technical assistance and for providing the polyethylene glycols and
ethanol for this study.

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Chapter 1: Introduction
1.1. Background of the Research: the Necessity for Stab resistance
Body armour is designed to guard against the threats of injury and even death; current
body armour offers the capability to protect the human body against ballistic threats.
However, the application environment of body armour is extremely complicated. For
example, in the battlefield, soldiers may encounter a variety of stab threats such as
direct attacks from knives and other sharpened instruments, or physical contact with
debris, broken glass and razor wire [1]. In the civilian sector, particularly in some
countries which apply strict gun ownership restrictions, the civilian police forces in
these countries have to face the rising threats with knives or other improvised sharp
objects [2].
The studies carried out by Taylor [3] and Stone [4] have indicated that there was an
escalating trend of stabbing injury and the correlating death rate since 1966, and have
shown their concern over such an increase [5]. However, more recent studies show that
the annual total of all types of assaults on police officers were relatively constant during
the period 1989 to 1997 [6], which kept around 18,000 per year, there was even a slight
decrease since 1991. Among these annual 18,000 assault incidents, around 1,000 were
classed as serious assaults, typically resulting in fractures, serious lacerations and
bruising, or concussion [7]. In mainland Britain, an investigation shows that a total of 29
police officers were killed in the line of duty over the period 1985 – 1995. Among these
cases, 9 road traffic accidents or incidents, 8 shootings, 7 stabbings and 5 from other
causes [8]. These data show that stabbing threats need to be treated as being similar in
importance as ballistic threats.
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From the side of police officers, they expressed their strong desire for improving the
performance of their personal defensive equipment. In 1995, an investigation of the
requirements for national police officers uniform was carried out by the United
Kingdom Association of Chief Police Officers (ACPO). The results of the investigation
were reported in October 1996 after a wide range of studies of all types of police
uniform and a series of surveys on 10% of police officers in England and Wales. The
surveys showed that almost 82% of officers expressed a desire for the personal
protection performance of the uniform to be improved [9]. This investigation illustrated
the fact that the performance of current protection equipment cannot satisfy the high
demand in actual use.

1.2. The Problems: Difference between Stab resistance and ballistic resistance
Ballistic resistance and stab resistance are two resistances which relate to impacting at
different velocities.
Ballistic resistance aims at resisting projectiles with high velocity and blunt shape, such
as various bullets. Ballistic protection is realised by the rapid conversion and
dissipation of kinetic energy from the striking bullet to strain energy of the ballistic
body armour system. Ballistic body armour disperses the kinetic energy of bullets
through deformation of the bullet, fibre fracture and propagation of an impact wave, as
is shown in Figure 1.1. This mechanism requires the textiles designed for ballistic body
armour to provide sufficient yarn mobility within the weave to propagate the impact
wave. Hence, bullet proof fabrics are not very dense, where the fabric density is usually
located from 7picks/cm to 9picks/cm.
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