Title: Protection of the Future

Subtitle: A Shock Absorbing Material that is Both a Liquid and a Solid

By: Hannah Brent, WRIT 340, 9AM section

Key Words: Physics, Mechanical Engineering, Material Science, Lifestyle, Ergonomics,

Entertainment

Author Biography: In Fall 2013, Hannah was a junior studying astronautical engineering at the

University of Southern California. She has been dancing since the age of 8 and has a passion for

finding the engineering applications in dance.

Author Contact information: hbrent@usc.edu

Prepared On: December 6, 2013

Prepared For: Marc Aubertin

Abstract

Dilatant non-Newtonian fluids are a part of our everyday lives, but very few know what

they truly are. They possess both fluid like and solid like characteristics, which sets them apart

from any other fluid. We see them in nature and childhood toys. Today, engineers are taking

these properties and applying them to a futuristic, shock absorbing material called d3o. The

possible applications of this material are endless, and it has the potential to revolutionize how we

approach protective gear.

Introduction

The majority of people today have enjoyed the wonders of putty at some point in their

lives. The seemingly solid yet fluid material has enraptured children and adults for years, but

only a select few know the science behind this multipurpose material. Putty is a toy to pass the

time, a cleaning mechanism, and a perfect example of a dilatant non-Newtonian fluid. This type

of fluid is found in everyday life, and is being used to make innovative, futuristic materials.

Dilatant non-Newtonian fluid is the foundation for one of the most advanced shock absorbing

materials called d3o. This material is designed so that its molecules flow in its’ normal state, lock

together under impact, and instantly return to its’ fluid state [1]. This innovative discovery has

applications in many industries, from sporting goods to cell phone protection.

Background

Dilatant non-Newtonian fluids do not possess the predicted characteristic properties of

fluids set out by Isaac Newton. The best approach to understanding non-Newtonian fluids is to

examine the much more familiar concept of Newtonian fluids. Newtonian fluids are what we

think of as a typical liquid in everyday life. A perfect example is water. The concept of viscosity

is what truly defines a liquid as Newtonian or non-Newtonian. Viscosity, or a liquid’s resistance

to flow, is the ratio of shear stress versus strain [2]. Newtonian fluids have a linear relationship

of this ratio. The term stress is simply,

σ= FA

where is the stress, F is the amount of force applied, and A is the area of application. Using

this equation, we see that more force applied to a smaller area will result in a larger stress. Strain

is a liquid’s reaction to stress. It can be defined as,

ϵ= δL

where ϵ is the strain, is the amount of deformation, or change in length, and L is the original

length. The viscosity of Newtonian fluids must be constant no matter the stress. This does not

mean that all Newtonian fluids have the same viscosity. For example, honey has a much higher

resistance to flow than water, but they are both Newtonian fluids because the value of viscosity

remains constant for each. This characteristic can be seen in tasks such as swimming. When you

swim, the water has the same resistance to flow whether you are moving slow or fast. The water

does not harden or become less resistant based on the force you apply to it.

On the other hand, non-Newtonian fluids do not have a constant viscosity. Instead, the

ratio of stress and strain varies depending on the force applied. So, if you apply more force to a

non-Newtonian fluid, it will not necessarily deform at the same rate. There are a couple different

types of non-Newtonian fluids, but dilatant will be the focus here. Dilatant, or thickening, fluids

are characterized by their ability to harden on impact. In other words, the shear stress applied to

the fluid causes an increase in viscosity, or more resistance to flow. If water were a dilatant non-

Newtonian fluid, then it would harden on impact if you were to dive into the water but remain

fluid if you slowly lowered yourself into the water. Obviously water does not fit into this

category, but there are many fluids that do. Dilatant non-Newtonian fluids are found in nature,

and they are the basis for inventions such as putty and d3o.

Natural and Early Man Made Examples

Have you ever wondered why it is easier to run on wet sand rather than walk? The

answer is dilatant non-Newtonian fluids. When sand is saturated, it acts like this type of fluid.

When walking, the application of shear stress on the wet sand is small. Therefore, the viscosity is

lower; meaning, the sand is more willing to move or flow. On the other hand, running causes

your foot to apply a greater stress on the ground. This causes the viscosity, or resistance, to

increase, which results in a more solid running surface. The greater the impact on the wet sand,

the more solid the surface. If we take the same principles and apply them to simple polymers, we

are able to see these characteristics in experiences of everyday life.

A common, homemade example of this type of polymer has been introduced to people

for years in the form of oobleck, but most have not wondered about the reasoning behind its’

behavior. The beloved science experiment simply combines 1.5 parts

cornstarch and 1 part water [3]. This gooey past time is a dilatant non-

Newtonian fluid. When this fluid is at rest, a bowl is required to contain

it. It is shiny in appearance, gooey in texture, and acts like a thick fluid.

The minute you crush it in your hands, it changes to a powdery solid

substance with the ability to return to its fluid state by releasing the

stress on the polymer. Oobleck is a fun pastime for many people, and one of the easiest ways to

physically see the characteristics of dilatant non-Newtonian fluid.

These characteristics can be seen in another childhood pastime, in the form of the

previously mentioned, putty. Putty can be molded and played with for hours without becoming

hard or drying out like play-doh. This is because it is in its fluid state, but most people have

discovered that by adding pressure, putty becomes harder to manipulate. This is why putty needs

to be worked when it comes out of the compressed casing. It displays the same characteristics as

oobleck but in a more processed form. Although putty has had success in the toy industry, its’

original use was a much more practical one. It was originally designed as an alternative to rubber

during World War II when there was a shortage of rubber [4]. Even though putty was deemed a

shorecrest.org

failure in this respect, it may have sparked the idea for a dilatant non-Newtonian fluid that can be

used for practical purposes. One such invention is d3o.

D3o: What Is It?

D3o is a dilatant non-Newtonian fluid that has been used in many practical applications.

Engineers have taken the characteristics of these fluids and created an amazing shock absorbing

material that hardens on impact while being flexible in its steady state. It shares characteristics

with oobleck and putty, but is more durable and stronger upon impact. The material exhibits

strain rate sensitivity. This means that the molecules of the

material react differently depending on the speed of impact.

When it is struck with normal speed, the molecules slide past

one another causing the fabric to have a flexible quality. When

asked to move faster, the molecules rearrange to lock together and form a shock absorbing

material. Referring back to our original equations, the viscosity, or resistance to flow, of d3o

becomes higher when more stress applied. The harder the impact, the more solid the material

becomes. The raw material “feels like something between Jell-O and Play-Doh” [1] (See figure

above). In its’ raw form, it can be torn apart, stuck back together, and have holes poked through

it as long as the impact is slow enough. A great visual is the ability to tear a piece of it slowly,

roll it into a ball, and immediately bounce it on the ground creating a large impact causing the

ball to bounce like a rubber bouncy ball and hold shape [1]. One of the most innovative aspects

of d3o is its ability to immediately revert from its solid form, during impact, to its’ elastic form

within seconds.

Primarily, d3o has been designed as a lightweight alternative for protective gear. It is

armor without the bulk and restriction of movement. D3o aims to be lightweight, durable,

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breathable, washable, and elastic. The material can be made millimeter thin, enabling it to be

implemented into clothing and padding without causing unnecessary mass [1]. Even in such a

thin form, the material maintains its strength and durability. The question is, why implement a

dilatant non-Newtonian fluid as protective gear when padding can do the same task? The answer

is that the ultimate benefit of d3o comes from the fluid characteristics. It provides protection

while enabling unrestricted movement. Unwieldy padding does not provide the same comfort.

The fluid state of the material is what makes it different, and the solid state is what makes useful.

Both characteristics of this dilatant non-Newtonian fluid make for a marketable, economically

sound alternative for protective wear.

Sports Equipment

The avid snowboarder and original inventor of d3o, Richard Palmer, says, “I recognize

that if I could build a material which made use of those liquid properties but was no longer a

liquid then that would be extremely useful in the context of snowboard protection” [5]. The first

market to see d3o implemented was sports equipment. It was first commercialized when the

American and Canadian alpine ski teams used the material in their ski suits for the 2006 Winter

Olympics. “Skiers normally have to wear bulky arm and leg guards to protect themselves from

poles placed along the slalom run” [6]. This prohibits maximum speed and restricts their

movements. D3o has been implemented into padding for their shins and forearms. The material

can be worn under their ski suits and allows for full range of motion with the necessary

protection. [6] The ski suits were a success within this community.

Since then, d3o has been implemented into many other forms of sports equipment. You can

find beanies that can act as snowboarding helmets due to the lining of d3o. It provides the

warmth and comfort of a beanie while having the capability to protect from injury in the case of

a fall. It has also been applied as mesh reinforcement in backpacks to hold skis. You can find the

material in polo knee protection gear, running shoes, motorbike gear, goalkeepers’ gloves, and

horseback riding clothing. The possibilities are endless. D3o is extremely appealing to the sports

world due to its lightweight material and strength under impact. It acts as a shock absorber,

padding, and wearable material. D3o products are giving consumers the ability to perform at a

higher level due to the elimination of limiting protective gear. It is bettering the activities.

Pointe Shoes

D3o is being used where people see a need for it. The possibilities are endless, but one of

the most unique applications is in the form of pointe shoes for ballet. Dancing en pointe, or on

point, has long been a right of passage for most ballet dancers and is the norm for anyone

studying ballet. Dancing on the tips of your toes can cause an enormous amount of stress that is

extremely painful and the catalyst for many injuries in dancing. If we go back to our definition of

stress as the amount of force applied divided by the area of application, we see why dancing en

pointe is so painful. While standing normally, you are distributing the force of your weight over

the area of your two feet. While en pointe, dancers are placing all of their weight on

approximately one square inch of space. This causes the

stress to become significantly higher.

In order for ballet dancers to rise to the tips of their

toes, a special shoe must be invented. “Imagine a shoe so

uncomfortable you have to hammer the insole and smash it

inside a door to make it tolerable. Now imagine tossing the same $70 shoe in the trash because it

shredded into pieces after just 45 minutes” [7]. The construction of pointe shoes is for support,

but that makes for an extremely stiff and uncomfortable shoe. The construction is for support,

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but in order for them to be useable, they must also be pliable. They must be pliable so the dancer

can roll through their feet during landings and intricate steps. This is so the dancer appears light

and ethereal. Therefore, the supporting shank (See figure above) must be broken in extensively

causing the shoes to be usable for only a short period of time. In essence, the breaking in process

is taking away the necessary support that the shoe was originally invented for. The design of

pointe shoes has not changed over the past 400 years, and d3o is one of the first innovations to be

implemented [8].

D3o’s unique ability to be flexible and solid depending on the amount of impact is

perfect for the application of pointe shoes. The d3o designed pointe shoes are lined with varying

millimeters of thickness of the material [7]. It allows the shoes to be flexible when under normal

stress, or not en pointe, and immediately supports and solidifies while en pointe due to the

increase of stress on the shoe. Also, the breaking in process is no longer necessary due to the

fluid characteristics of the material, therefore making it more economic. D3o is revolutionizing a

technology that has not been changed in hundreds of years.

Other Applications of D3o

Some other markets that d3o has been applied to are phone cases and military equipment.

The shattering of phones has always been a problem in the age of touch screen. With a d3o

phone case, you will have the comfort of a soft, flexible case and the protection. The dilatant

non-Newtonian characteristics make for a perfect balance of comfort and security. There is also

research being done for a bulletproof vest made of d3o material. The theory behind this is that

the higher the stress or impact, the more solid the material becomes. This would enable people to

have a lightweight, flexible vest that protects just as well, if not better, than the current vests

being used. It is still in the research phase, but the applications could be amazing [9].

Conclusion

Dilatant non-Newtonian fluids are a natural phenomenon that can be seen in everyday

life. The engineered version of these fluids has the potential to span every walk of life. These

modern advances can be seen in the form of d3o. This futuristic material has the capacity to

change societies approach to many topics from phone cases to pointe shoes. The use for dilatant

non-Newtonian fluids is endless, and society is mostly unaware of the engineering behind these

“simple” products. The majority of us have been exposed to dilatant non-Newtonian fluids from

a very young age in the form of putty or oobleck. Now, we are seeing this technology cross over

to our adult lives through phones and sports equipment. These innovative fluids have been with

us our entire lives from our toys to our walks on the beach. The research being done with d3o is

highlighting the remarkable properties that have gone unnoticed our entire lives.

References

[1] Brett Zarda. (2009, August 14). “The Incredibly Wide World of Smart Material D3o.”

Popular Science. [Online]. Available:

http://www.popsci.com/gear-amp-gadgets/article/2009-08/incredibly-wide-world-smart-

material-d3o.

[2] “Viscosity.” Encyclopaedia Britannica. [Online], 2013. Available:

http://www.britannica.com/EBchecked/topic/630428/viscosity.

[3] Mossy. “Oobleck.” [Blog]. Available: http://mossymossy.com/?p=298.

[4] (2013, August 19). “Weird Science: The Accidental Invention of Silly Putty.” KIDS

Discover. [Online]. Available: http://www.kidsdiscover.com/quick-reads/weird-science-

the-accidental-invention-of-silly-putty/.

[5] (2009, May 27). “Shock Factor-D3o.” physics.org. [Online]. Available:

http://www.physics.org/featuredetail.asp?id=35.

[6] Will Knight. (2006, February 14). “US and Canadian Skiers Get Smart Armour.” New

Scientist. [Online]. Available: http://www.newscientist.com/article/dn8721-us-and-

canadian-skiers-get-smart-armour.html#.UmD9vShem0s.

[7] Brett Zarda. (2008, May 14). “The Modern Twist on an Ancient Shoe.” Popular Science.

[Online]. Available: http://www.popsci.com/score/article/2008-05/modern-twist-ancient-

shoe?dom=PSC&loc=recent&lnk=2&con=the-modern-twist-on-an-ancient-shoe.

[8] (2008, May 16). “New Technology With a Good Pointe.” Sky News. [Online]. Available:

http://news.sky.com/story/603794/new-technology-with-a-good-pointe.

[9] Chris V. Thangham. (2009, March 1). “UK Military Uses New D3o Gel In Armor to Stop

Bullets.” Digital Journal. [Online]. Available: http://digitaljournal.com/article/2683