Appel 43.1 - Micro

DE APPEL
MICRO
WATCH
ENGINEERING
VISUAL
CAMPUS QUARAN-
TAINE
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j
43.1
Het verenigingsblad van W.S.G. Isaac Newton
A SOFT TOUCH:
SECRET POWER OF
MICROFLUIDICS

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CHAIRMAN’S NOTE
63
Welcome to the first Appel edition of the academic
year! And for all new students, welcome to
maybe even your first edition of the Appel ever.
I hope that everyone enjoyed the first months of
the new academic year, despite it being different
than usual. Personally, I had a lot of fun with the first lustrum activities.
The committee did great work for a spectacular opening drink
and a very nice port tasting. And not to forget, we’ve had countless
DJ’s from our own association turning our self-isolation into a party
with the lustrum radio, live from Diepzat.
Anyways, back to this new edition of the Appel. Most mechanical engineers
like big chunky robust machines and constructions. This is a
logical mindset, more steel is more better, right? For example, during
our 55th Dies we went for the record of biggest apple pie ever made,
resulting in an astonishing and moreover very delicious cake of two
square meters. However, just as important as grandiose is the many
tiny details that every big construction is made up of. Therefore the
theme of this edition is ‘micro’.
Some interesting things of ‘micro’ with big effects are coatings, which
can make an object resistant to water, wear, erosion, et cetera. Another
great example is a computer or phone. Millions of tiny transistors
can get a big job done. And when the performance of one tiny
transistor can be improved slightly, the effects will be enormous.
Furthermore, there are very elaborate studies and work fields consisting
of one simple task: trying to get things smaller. This might be
a type of engineering that goes against our nature, but being small
can have some serious advantages like easier transportation, cheaper
production, and sometimes just to blow people’s minds with new
technology.
I would like to finish this introduction with some advice. It is not the
physical size that matters, but the greatness of the performance.
I wish all of you lots of fun reading this new edition of the Appel!
Jonne van Haastregt
Chairman of W.S.G. Isaac Newton
Adunare Utile Dulci

INHOUD
Colofon
De Appel is een uitgave van het werktuigbouwkundig
studiegenootschap Isaac
Newton in samenwerking met de opleiding
Werktuigbouwkunde aan de faculteit
der Construerende Technische Wetenschappen
van de Universiteit Twente.
Redactie-adres
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[E] appel@isaacnewton.utwente.nl
Uitgave
Jaargang 43, nummer 1, december 2020
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© 2020 de Appel
De redactie is op geen enkele wijze
verantwoordelijk voor de inhoud van de
aangeleverde kopij en houdt zich het recht
kopij in te korten en te wijzigen.
Hoofdredacteur
Almer Lagerweij
Eindredacteur
Michiel Louwé
Grafische vormgeving
Fedde Engelen
Jeroen van den Hoogen
Redactie
Ekaterina Antimirova
Roland Guijs
Alicia Knijnenburg
Fausto Visser
Sabine van der Werff
Hugo Wesselink
Danique Wetsteijn
Drukker
Drukbedrijf.nl
Joan Muyskenweg 114
1114 AN Amsterdam
Advertenties & Advertorials
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06
A Soft Touch: Secret Power
of Microfluidics
A rising, sensitive technology
12
Microraptor
The four winged predator
14
Jelle Korblet
De wielen van
31
The little war
Building with Lego
4
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16 Microgravity
20 Watch exposition
Visual
24 Association News
27 Micro huisdieren
Klein formaat, grote
gevolgen
31 Campus quarantaine
Column Hugo
36 Temperature and
strain rate dependence
for end-loaded unidirectional
glass-polypropylene
composites
Graduation article
REDACTIONEEL
Na een paar hele snelle eerste maanden zijn we
onderhand al aanbeland in de tweede module
van dit academisch jaar. Ik hoop dat jullie
allen het eerste kwartiel goed gepresteerd
hebben en jullie cijfers je bevallen. Of je cijfers
nou mee- of tegenzitten, maakt nu even
niet uit, want het is nu tijd voor de eerste Appel van dit jaar.
Langverwacht en naar gesmacht door velen. We hebben een
(te korte) zomerstop achter de rug en zijn weer helemaal vers
voor jullie lezers aan het werk gegaan. Onze redactie heeft
weer wat mooie onderwerpen aangesneden, en dankzij de
grafici ziet het er allemaal messcherp uit. Of je tentamen- en
projectcijfers een 6 of een 8 waren, maakt niet uit met het
thema van deze editie, micro. (Tenzij je cijfer een 6 µ was).
De meeste van ons WB’ers houden van gigantische machines
en constructies. Deze editie gaan we proberen je toch
wat van gedachte te doen veranderen, en je het mooiste van
de hele kleine wereld te laten zien. Micro beïnvloedt immers
macro. Hoe proberen we je van gedachte te veranderen? Misschien
lukt dat al als je leest over micro-zwaartekracht, wat
astronauten ondervinden in het ISS bijvoorbeeld. Wat nog
meer op microschaal is, maar wel gigantische gevolgen heeft
zijn processors. In bijna elk elektronisch apparaat wat je gebruikt
zit het wel, maar de rekenkracht dat zo’n microscopisch
chipje heeft is ondenkbaar. Mocht dit allemaal je nog
niet overtuigd hebben dan zijn er nog microfluidics. Manipulaties
van vloeistoffen in sub-millimeter schaal. Haast ondenkbaar,
maar met ondenkbaar veel applicaties. Daarnaast
is een oude rubriek nieuw leven ingeblazen, sommige ‘oldtimers’
onder ons zullen het nog wel kennen; De wielen van!
Met deze editie, Jelle Korblet.
Mocht je nieuwsgierig zijn geworden nu je dit hebt gelezen,
schroom niet en lees gauw verder. Dit was nog maar het
tipje van de sluier en ik beloof je nog veel meer microscopisch
vermaak. Hierbij onze ode aan de kleine wetenschap,
veel leesplezier.
Almer Lagerweij
Hoofdredacteur
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A SOFT TOUCH:
SECRET POWER OF
MICROFLUIDICS
A rising technology to help your grandparents
feel, veterans move, and more sensitive and
fragile operations take place.
BY EKATERINA ANTIMIROVA
As part of the Mechanical Engineering study, we learn,
analyse, and calculate rigid bodies. Endless hours are
spent on calculating their tensile strength graphs and
failure mechanisms. Well, truth be told, after all that work,
these rigid bodies are not even as useful as one may hope.
When actuated, these rigid bodies are not helpful when
handling soft and biological materials. This is why we need
soft robotics. They tackle the most interesting motions via
the most weak means, fluids, called microfluidics. Currently,
there is a massive gap in the application of microfluidics in
soft robotics, allowing those who jump on this train to steer
development of this technology and spin off companies.
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WHY RIGID-BODIED MECHANISMS ARE NOT AN
ALL-PURPOSE SOLUTION?
First of all, hard robotics and flexure based mechanisms maintain their
shape and material structure, whereas soft robotics adopts a new shape
and adjusts stiffness based on a required application. This sort of operation
was inspired by nature, specifically muscle movement. Imagine a
cheetah as it sets off to catch its prey. Its eyes are set dead on a target as
it leaps forward, but the terrain is changing. It is changing from a rocky
stone where the cheetah was hiding to some soft grass. Its paws and
legs need to compliantly match this new environment. When the cheetah
successfully catches its prey, its jaws need to rapidly adjust their
deadly grip. If every move had to be calculated and individually controlled,
it would be an impossible calculational task. This, in part, is because
there is an infinite amount of degrees of freedom in the body. Besides,
if its limbs were made from a metal with a high modulus of elasticity,
the cheetah would not be able to adjust their stiffness. Potential internal
damage of its organs could follow as result of high contact forces. Hence,
an ideal soft robot would have to exert some if not all of the described
characteristics. This robot must achieve its tasks via adjusting its stiffness
to a given environment and absorbing impacts. For example, use
of soft grippers to handle animals and fragile materials will decrease a
likelihood of their injury or damage. Besides when technology finally
allows robots to operate on humans, you would want this robot to have
built in compliance to prevent some unintentional scratching and stabbing.
Therefore, a basic purpose of soft robotics is to allow for a careful and
safe interaction with humans and animals and manipulation of fragile
materials. This task will be achieved when actuators and materials allow
for programmable adjustment of robots’ stiffness and shape. This
means a soft robot can only be as good as the technology behind its
actuation and composition. For example, a perfect muscle has not yet
been recreated. This is when state of the art technologies like microfluidics
enter the stage.
WHAT ARE MICROFLUIDICS AND WHAT MAKES
THEM SO SPECIAL?
There is no clear definition to the concept of microfluidics. The prefix
“micro” is used rather loosely, since the devices range in size from as
low as the nano level (10^-9 m) to more a understandable millimeter scale
(10^-3 m). So we call any device a microfluidic device if it operates via
fluids within these scales. Conveniently, most of them do fall in the
micro scale (10^-6 ) range. Larger devices are referred to as conventional
fluidic devices. This is why the definition of microfluidics, “The science
and engineering of systems in which fluid behavior differs from conventional
flow theory primarily due to the small length scale of the system”,
is rather vague.
Microfluidics are not well known within mechanical engineering study
primarily due to their original application in chemical and biological
particle analysis. In these fields, microfluidics have several physical advantages
over conventional fluids. On a smaller scale, fluids are more
laminar; particles flow smooth and straight without turbulence. This
simplifies mathematical analysis and helps to precisely predict their
behavior.
Additionally, capillary forces dominate over gravitational forces. These
forces are the reason why tea climbs up the tea bag and spills onto the
table. On a smaller scale, molecules always strive to decrease their surface
energy. Therefore when placed into a sufficiently small channel or
a porous material, like the tea bag, water particles will try to fill it. The
intermolecular forces between particles will keep water together even
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when it defies gravity. Together laminar flow and capillary
forces allow for ideal dispersion and faster diffusion.
Using these principles, chemists and biologists developed
complex microfluidic circuits and measuring devices, like
blood glucose meters and pregnancy tests.
Unfortunately, many of these scientists were too preoccupied
with this microfluidic technology. They neglected
to produce research with commercial or practical applications.
Currently, microfluidics are experiencing a revival
thanks to a close collaboration between new generations
of scientists and engineers.
HOW MICROFLUIDICS CAN BE AP-
PLIED IN A SOFT ROBOT?
design, pressure opens and closes the gates. This controls
whether or not a microfluid can pass through.
This year researchers from the Chonnam National University,
South Korea, published a paper on a new concept
of a 3D slope valve which precisely controls fluid flow.
Through either improvement of functions or revision of
control of microfluidic circuits, researchers are now working
tirelessly to replicate functions of integrated electric
circuits (IECs) into integrated microfluidic circuits (IMCs).
Depending on the amount of programmable actions, soft
robots will be able to sense, move, and interact with their
surroundings.
CONTROL
A recent result of this collaboration has been an introduction
of microfluidics into some soft robotics devices.
In 2016, Harvard presented the first entirely autonomous
soft robotics device, an octopus shaped robot named Octobot.
Microfluidics powered, controlled, and actuated it.
Octobot did not look too phenomenal and its tentacles appeared
to rather twinge than produce a smooth motion,
but it was a start nevertheless.
A complete integration of fully microfluidic control is a
reason why this was such a prominent project. Microfluidics
and regular fluids are a good source for smooth and
compliant movement of a robot. For example changing
pressure can alter the shape of the silicon (or another soft
material), so there is nothing groundbreaking there. However,
prior to Cctobot, the traditional control of these
motions was done via hard electronics and batteries or
other external connections. Naturally, use of rigid electronics
significantly reduces the compliant behavior of
robots and, therefore, their effectiveness.
Beginning with fuel storage and ending with actuation, all
tasks are done via microfluidics within the Octobot. The
power comes from the chemical reaction which explodes
liquid fuel into a gas. This gas fills 3D printed cavities of
the silicon based body, which expands them, causing respective
twitching. The brain of Octobot is a microfluidic
logic circuit, and it controls when the chemical reaction
should take place. This microfluidic circuit functions similarly
to an electronic oscillator where the inductor and
capacitor exchange energy creating an alternating current.
The exchange continues until the robot runs out of
fuel, and friction within channels decreases the current
to zero. According to the Nature Magazine, one milliliter
of the liquid can support Octobot for around 8 minutes [6].
Research to increase and improve functions of a microfluidic
circuit, and thus expanding what it can actually do,
is an ongoing process.
Back in 2011, a group from the University of Michigan,
USA, proposed a design of an elastomeric valve based system
which functions as a self regulating circuit. In the
MANUFACTURING
Two years after the release of Octobot, the same team
from Harvard presented another eight legged silicon
creature, a peacock spider. This soft robot combined microfluidic
control with newly developed microfabrication
techniques to achieve a wider range of motion. Not an expanding
gas but dyed water allows it to squat and balance
on its eight colorful legs. With an increased amount of
channels and interwindings, degrees of freedom and complexity
of the movement increase, approaching the ideal
of a muscle.
But, the spider is still far from this ideal. Its body and legs
are made from twelve layers of stacked silicon allowing
for varying stiffness. The channels and their sizes merge
between different layers. Larger cavities span more layers,
for example. When fluid fills one of knee cavities, the
compliant layers expand under the pressure, thus forcing
the leg to bend. The group from Harvard calls this process
injection-induced self-folding. The control of bending the
eight legs allows for a variety of different motions.
There are different ways to create these patterns of cavities
and channels. The industry standard for many years
has been soft lithography. Simply put, this process transfers
the pattern on a photomask to the surface of a silicon
wafer using UV light. There are many steps and preparation
procedures in this process. The main steps are: (1)
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placement of a photoresisting material onto a silicon base; (2) shining
UV light onto a photoresist through a photomask depicting the design;
(3) removing the photoresist exposed to UV light, and (4) chemically etching
silicon from areas not protected by the layer of photoresist. This
process creates precise cavities for a microfluid to follow.
When manufacturing their peacock spider, the group from Harvard
developed a new microfabrication process, which combined soft lithography
and laser machining. In the future, more complicated interwindings
between channels and more sophisticated geometry of silicon
layers will allow for an even greater range of motion. Therefore, not
only microfluidic control must be developed for this to happen, but also
an improved channel fabrication is needed for fluids to actually create
the smooth motion.
SOFT ROBOTICS IN CONTEXT
Microfluidics is not the sole way to control soft robots. Traditional electronics
and batteries are more technologically advanced than their
microfluidic alternatives, and often they scale better to a micro level.
Micro valves and pumps are bulkier, for example. Therefore to examine
a particular aspect of soft robotics, researchers often rely on the traditional
options. For example, when only the geometry of the body is
of interest, the researchers may choose to actuate the soft robot via
regular electronics.
In other cases a completely soft robot is not necessary, making a hybrid
option the most logical choice. Reduction of degrees of freedom
could be done to decrease computational power. Moreover, soft robotics
are not meant to substitute rigid robotics altogether even when their
technology, like microfluidics, does catch up. They serve different purposes,
and therefore there is no competition. Soft robotics, however, has
a long road ahead to fulfill its purpose. Research to improve microfluidics
with respect to soft robotics is well underway, but it is still in its
infancy. Just two years ago, a single twitch of Octobot was a success.
Many can choose to doubt the necessity for the effort to develop the
field from scratch when rigid robots, like ones from Boston Dynamics,
approximate live dynamics so well. But they are exactly that: they are a
rigid approximation. The only way to achieve absolute compliance is to
forego all traditional rigid technologies.
When it comes to micromanipulation, surgery, and wearable devices,
soft robotics are a road to take. For a veteran coming home with an
unfortunate injury wishing to truly walk again and play with his or her
children, no rigid L-shaped prosthetic will substitute a compliant and
natural biocompatible option. Scientists studying coral reefs, animals,
or taking care of other humans, soft robotics will allow for less invasive
and careful manipulation.
“Too often we underestimate the power of a touch, a smile, a kind word,
a listening ear, an honest compliment, or the smallest act of caring, all of
which have the potential to turn a life around” (Leo F. Buscaglia). When
sitting behind a desk, designing robots and running a finite element
analysis, anyone will feel impersonal. The lines of code do not predict
smiles and tears of joy. We engineer the world to make it a better and
safer place, to ease the struggles and to help those in need. Soft robotics
is an underdeveloped field, and it is far more complex than most manipulation
methods. We are not doing engineering because it is easy. We
are doing engineering because it serves the people. a
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ADVERTORIAL
WHEN OP-
PORTUNITY
KNOCKS,
DARE TO
OPEN THE
DOOR
Experienced people know that careers are founded on as
much luck as judgement and skill, as Arnela Masic discovered
during her engineering studies in 2015. One lucky moment
put her on a path to the career she enjoys today: she forgot
her lunch. “A friend suggested I could get a free lunch at
an ASML-hosted lunch meeting on campus that day. It was
there I learned about the ASML scholarship. I applied and
was eventually selected – it felt pretty special as only 25
scholarships are on offer in the Netherlands each year.”
Through the scholarship, ASML supported Arnela through a
Masters in Systems and Control, which then led to her joining
the company in 2017.
NOTHING “GREY-HAIRED” ABOUT IT
“Everybody at my university had heard of ASML – the logo is everywhere.
But what they did there was more of a mystery. For me personally,
‘lithography’ did not sound as interesting as other technical industries
like aerospace or automotive. I was picturing grey-haired guys
doing boring experiments. It wasn’t until I got to know them through
the scholarship that I realized there’s nothing ‘grey-haired’ about it.
There are so many different careers here, with such diverse, supersmart
people. It was nothing like I expected.”
ENGINEERING AND SO MUCH MORE
“I was looking for more than just a ‘technical’ job. After learning about
the many different careers on offer, the role of Customer Support Applications
Engineer really appealed to me. I get to travel to customer sites
around the world – the US, Korea, Japan, China and Taiwan - and work
on projects to improve the performance of our lithography systems. I
get to use my engineering knowledge – not in terms of always knowing
the answers, but in terms of applying logic, troubleshooting, analysis
and identifying which experts can help – and I combine it with communications,
project management and implementation. There’s great team
spirit; I’m supported by a wide network of experienced colleagues who
all help each other.”
AN IDEA WORTH MILLIONS
“And I receive lots of training, both technical and non-technical – soft
skills like customer focus and influencing without power.” Arnela quickly
found out how useful her newly acquired skills are. “There was project
at a customer where it was important to prove a certain output of a
machine in order to make the sale. However, at that moment, there was
an issue with one of the machine parts that would not have helped my
demo test. My training helped me convince people to make this issue
a priority over their own projects, resulting not only in a permanent
solution, but also in the sale of the system worth millions!”
ARNELA’S ADVICE – ‘GO FOR IT’
“My advice is if something about a job sounds interesting then don’t
overthink it, just try it, because you never know exactly what you will
be doing on a day to day basis. That’s ok, nobody does when they start.
But at companies like ASML, you will have excellent training, support
and inspiring colleagues, so there’s no need to be afraid to go for it.
When opportunity knocks, dare to open the door. For me, there’s has
literally been a whole world to discover, and I’m really enjoying the journey
– it was worth stepping into the unknown to start it.”
Are you interested to learn more about ASML? Visit www.asml.com/
students for more information about our events, internships and scholarship
program.

ADVERTORIAL
COMPANY PROFILE
ASML is a high-tech company, headquartered in the Netherlands. We manufacture
the complex lithography machines that chipmakers use to produce integrated
circuits, or computer chips. Over 30 years, we have grown from a small
startup into a multinational company with over 60 locations in 16 countries
and annual net sales of €11.8 billion in 2019.
Behind ASML’s innovations are engineers who think ahead. The people who
work at our company include some of the most creative minds in physics, electrical
engineering, mathematics, chemistry, mechatronics, optics, mechanical
engineering, computer science and software engineering.
Because ASML spends more than €2 billion per year on R&D, our teams have
the freedom, support and resources to experiment, test and push the boundaries
of technology. They work in close-knit, multidisciplinary teams, listening
to and learning from each other.
GET IN TOUCH WITH YOUR
ASML CAMPUS PROMOTOR!
SANDER GEURTS
sander@workingatasml.com
If you are passionate about technology and want to be a part of progress, visit
www.asml.com/careers.

MICRORAPTOR
THE FOUR WINGED PREDATOR
DOOR DANIQUE WETSTEIJN
While many of the topics in this edition are
about very, very small things, this article will address a very, very old
thing. It’s dinosaur time! And although dinosaurs couldn’t really be
categorized to be small, one of them has a really convenient name:
The Microraptor. This ancient creature is very interesting to tell about
regarding history, evolution, but also aerodynamics. And fortunately
it’s also small!
When we are talking of dinosaurs the first thing coming to mind are:
The T-rex, the velociraptor, the stegosaurus or any other of those gigantic
reptiles walking around in Jurassic Park. But the microraptor
is more comparable to a large bird, like an owl or an eagle. But with a
very long tail, feathers over its complete body and four wings. Scientists
have estimated the length of a full grown microraptor to be 70 - 120 cm,
a height of at least 40 cm and weighing 1 kg. In 2012 research has been
done with the pigment cells in a new specimen. The structure of the
cells was found to be similar to that of the starling, a bird really common
to find in the Netherlands. Like the starling, the microraptor had a
blue metallic color that reflected light beautifully.
Something that a lot of people don’t know is that all birds we know nowadays
have a direct line to dinosaurs. Birds and dinosaurs have many
similarities. Their digestive system makes use of gastroliths, their bone
structure is hollow and include many pneumatic bones, they build
nests, lay eggs and brood them. Actually, that makes sense, doesn’t it?
We know several land dinosaurs that had feathers around their heads,
their legs or were even completely covered in it. And if you ever have
seen a plucked chicken, you know it’s basically a Tyrannosaurus Rex
that lost his deep voice after a rough night of partying …
That the microraptor was a predator and creative hunter has been proven
several times in the past 10 years. Besides the obvious claws that
were discovered in well preserved fossils, its gut contents told us even
more. Not only did the microraptor eat small mammal-like animals that
lived around trees, also smaller birds were swallowed whole and fish
couldn’t escape this dinosaur bird either. This suggests that the microraptor
did not only live amongst trees, but also close to lakes and seas.
Let us pay some attention to the fact that the microraptor has four wings
instead of only two. The microraptor is a special kind of avian dinosaur,
as it is an important historical link that strongly supports the fourwinged
stage of bird-evolution. Although it may be hard to imagine for
us right now, having four wings was trending topic in the dinosaur era.
There are multiple classes of bird-like dinosaurs with feathers attached
to the arm limbs and the leg limbs, resulting in four wings. But only the
microraptor family was discovered to be able to actually use the ‘leg
wings’ for flying or gliding purposes. As it was able to arrange its leg
limbs much alike a flying squirrel while gliding. This was determined
after carefully studying the hip bone structure. Moreover, the feathers
attached to the leg limbs of the microraptor were much longer and had
higher structural stiffness than on other dinosaur birds, creating four
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aerodynamic surfaces with suitable
properties for midair maneuvers.
In 2014, Dennis Evangelista and his very large
research team did wind tunnel experiments on a
3D-printed and scaled model of the microraptor. This
model was based on what experts thought it must have looked
like. The research team wanted to find out how having four
wings and being able to arrange leg limbs in various positions
affected the flying capability of a feathered dinosaur.
A bird or bird-like animal can use its wings in three ways. The
wings can act like a parachute, decreasing falling velocity while
dropping from a tree; they can be used as passive gliders, for
levitating as long as possible; or be used in “true flight”. The
latter is the situation where occasionally flapping wings create
thrust and all aerodynamic surfaces create enough lift compared
to drag and gravitational forces to maintain or even increase
altitude. The wind tunnel experiments showed that the “parachute
function” was not possible as the wings were too narrow
and were not having a suitable curvature. Gliding and flying
was determined to be very possible and even likely for the microraptor.
As the microraptor had two extra wings that could be
arranged in many configuration, several flying specifics could
be created, just by moving its legs. After the wind tunnel experiments,
the researchers concluded that adding two extra aerodynamic
surfaces vertically (legs down) provided stability and
more maneuverability.
Horizontally (legs up) these surfaces provided a double amount
of lift, which makes the total amount of lift more likely to be
enough for the “true flight” situation.
The microraptor would be able to
achieve true flight with only two wings as
well, provided that their arm limb wings were
much longer than they were. This is an indicator
that the natural habitat of the microraptor included narrow
spaces, for which long arm feathers would be inconvenient.
Mankind has been copying many concepts of nature before. As
also we know aircrafts making use of these aerodynamic tricks
of this four winged predator. Think of tandem winged aircrafts,
of which a so called “Delanne wing” mimics the aerodynamic
geometry of the microraptor most.
If the microraptor would be able to align its hind winds perfectly
with its front wings, then one can compare its flying abilities
with a “Canard”. These aircrafts can do impressive maneuvers in
mid-air like loops, corkscrews and abrupt turns.
Regardless of any fancy wing configurations, the microraptor
needs his tail to change direction while flying. A little sweep left
or right changes the air flow and hence the flying direction. But
also does the tail help to swift its center of gravity to make fast
and sharp curves. We find this vertical stabilizer in fixed form as
well on every single flying aircraft, namely the fin on the back!
All together the microraptor had interesting features, making it
almost a pity it is not flying around nowadays anymore. Luckily
we are able to fill the skies with our own impressive birds of
steel. With or without feathers… k
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De Wielen Van
JELLE KORBLET
In de collegezaal zie je
genoeg auto’s op de
bureaubladachtergronden van
WB’ers. Ook wordt er in de
gangen van de horst vaak genoeg
gesproken over paardenkrachten,
wegligging, topsnelheden en
nieuwe technieken om het
eerdergenoemde tot een hoger
niveau te tillen. Maar net zoals
bij seks wordt er meer over
gepraat dan gepraktiseerd. Maar
er zijn uitzonderingen, een aantal
WB’ers heeft niet alleen een twee
wieler voor het vervoer naar de
collegezaal maar ook een vierwieler
erbij. Vanuit de Appel gingen we
opzoek naar deze uitzonderlijke
WB’ers, met de vraag of ze over
hun auto wilden ouwehoeren.
14 DE APPEL
DOOR FAUSTO VISSER
FOTO’S AUDI MICHIEL LOUWÉ
Voor deze eerste editie van de hernieuwde rubriek bijt Jelle het spits af. Als 29-jarige masterstudent
pakt hij het even anders aan en heeft zelfs meerdere vierwielers tot zijn beschikking.
AUDI 100
De automechanische avonturen van Jelle begonnen met een Audi 100, deze was samen met maten
gekocht onder het mom van een cross auto. Gekocht bij het inbeslag genomen spul van de
politie voor 406 euries. Dit allemaal voordat Jelle zelf 18 was. De auto had al een paar jaar zonder
APK stil gestaan. Echter was het wel de meeste luxe uitvoering van de 100, met een 2.3L vijf
cilinder blok in combinatie met een handbak. Gedurende een jaar werd in rustig tempo de auto
weer opgelapt en rijklaar gemaakt. Naast wat schoonmaakwerk waarbij mos en een vogelnestje
onder de motorkap werd verwijderd moesten natuurlijk ook de standaard dingen aangepakt
worden. Nieuwe accu, remmen vervangen en nagelopen etc. Na deze opknap beurt heeft de Audi
in goede toestand veel kilometers mogen maken op vakanties en allerlei andere trips, zelfs de
Nürburgring heeft ie nog mogen zien.
Ondertussen gaat de Audi van Jelle al lang mee, hij heeft al de dertig jaar aan mogen tikken, wat
ook gunstig is met de APK intervallen die vanaf dan tweejaarlijks zijn. Qua wegenbelasting viel
het sowieso al mee, vroeger maakte men namelijk nog grote ‘auto’s’ die niet twee ton wegen.
Met zijn 1200 kilo de Audi 100 dan ook een relatief lichte auto. Aangezien Jelle best veel rondrijdt
met de Audi wil hij nog wel groot werk verzetten aan de auto maar komt dat eigenlijk niet goed

uit zolang er nog geen tweede auto
is die de last samen met de Audi kan
dragen. Mocht dat zo zijn, dan zouden
de volgende zaken aangepakt
gaan worden; De velgenranden kunnen
wat werk gebruiken, de randen
zijn wat gecorrodeerd, dus op het
moment lopen de banden mondjesmaat
leeg. De airco heeft ook eigenlijk
een nieuwe pomp nodig. Nu
is het even wachten tot het buiten
echt lekker koud is of de airco pompen
nog wat goedkoper worden.
FORD BUS
Het tweede voertuig dat Jelle veel
gebruikt is een Ford Transit Mk2 uit 1980. Deze heeft Jelle samen met een collega gekocht
van een lid uit de Simca club van zijn collega in februari 2018. Die beste man had
een Bierwinkel in Leiden, dus zat de bus natuurlijk helemaal vol geplakt met stickers
van zijn winkel. Maar hij wilde er graag van af omdat de bus uitermate slecht liep.
Gelukkig bleek het een bekend probleem te zijn met de automatische choke van de
carburateur, maar dat wist de verkoper nog niet. Deze was zelf ook in bezit van twee
linkerhanden dus die wilde er graag van af. Voor een kleine duizend euro is deze bus
van eigenaar veranderd naar Jelle en zijn collega. Nu kan de bus veel gebruikt worden
voor allerhande zaken, verhuizen, tijdelijk slapen, etc. Terwijl hij ook al richting de
veertig jaar oud gaat.
aVW PASSAT
De laatste vierwieler beschrijft Jelle meer als een
Kermis auto, deze heeft ook een interresant verhaal.
Voor de Carbage run heeft hij deze met een paar maten
uitgezocht, specifiek omdat ze op zoek waren naar
vierwiel aandrijving met toch een beetje por onder de
motorkap. Voor de Carbage run mag het natuurlijk wel
wat aandacht trekken en herrie maken. Het werd een
passat uit 1999 met een 2.8L V6. Herrie maken dat doet
de Passat zeker, omdat het thema de NS was zit er ook
een enorme toeter op. Dit thema was snel gevonden
omdat de twee maten van Jelle bij het spoor werken.
Zo zijn er zoveel mogelijk logo’s van de volkwagen vervangen
door echte NS pijlen, is er een bewegende pantograaf
op het dak gemaakt en komt de verlichting aan
de voorkant in de buurt van een goede loc. Door hard
te crossen door het bevroren en sneeuwigge noorden
en maffe opdrachten uit te voeren heben ze ook nog de
Carbage run kunnen winnen. Deze overwinning kwam
onder andere door het passeren van de finish met een
vis bevroren in een blok ijs.
Ook mooie wielen? Neem contact op
met de Appelredactie!
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MICROGRAVITY
BY ALICIA KNIJNENBURG
Have you ever looked at space and imagined yourself being there? Seeing Earth’s
surface from a completely different view. Not only the view, but also the feeling of being
weightless must be incredible. You do not have to go all the way to space to experience
being weightless. It is also present here on Earth. You only need to know where to look.
WHAT IS IT?
The name microgravity already speaks for itself: a very small amount
of gravity. It is also referred to as weightlessness since objects or people
appear to be weightless in it. It should be noted however that the gravity
will not be exactly zero, but just very small. Gravity works between
objects with a mass. For it not to work, you have to be very far away
from an object. However, environments can be created where you do
not have to be far away and still experience microgravity. Astronauts,
for example, who float in their spacecrafts or the fact that they can lift
the heaviest objects with just one hand or finger. Those experiences are
possible because of microgravity.
HOW TO CREATE IT?
Being in a state of microgravity means that no other forces should be
present. One way of doing that is by being in a free fall. It also means
that air drag cannot be present, as it is with for example skydivers.
16 DE APPEL

Therefore, drop towers are created. These towers are often very high, up
to 150m, and the air is pumped out of it. Objects are then shot to the top
of the tower and dropped. The objects are in microgravity during their
fall until they crash on the ground. Of course, this crash is not ideal, but
the research can tell us a lot about microgravity.
Another place where microgravity exists is inside the International
Space Station ISS. The station has a specific speed and altitude. It orbits
around Earth 15 times a day at an altitude of 400km making it appear in
free fall. Experiments with microgravity at the ISS are conducted to get
more insight. One of the outcomes is that the human body loses bone
and muscle mass while being in a microgravity environment. Because
of this research, together with other studies and technology, improvements
could be made to treat osteoporosis.
Astronauts have to train a lot before going into space. One of the ways
to get used to the microgravity environment is a reduced-gravity aircraft
or parabolic flight. Some refer to it as the vomit comet, since the
near-weightlessness experiment can be quite hard on the stomach. The
environment is achieved by following a parabolic flight path relative to
the center of the Earth. At some points during the flight, the object and
people inside are in free fall. In this way, the astronauts can get used to
the feeling of orbiting the Earth.
HOW CAN IT BE USED?
Wherever you are, a gravitational force is present between you and another
object. You do not even think about it as it is there all the time.
However, it makes the Earth orbit the sun and the moon orbit around
Earth. It makes the apples fall from the tree. Now imagine it not being
there. You would feel weightless on Earth itself. While this is a very
interesting experience for you, it is also interesting for scientists. Since
gravity is always present, it has an influence on all research and scientists
have to take it into account in their experiments. Working in a
microgravity surrounding therefore opens new doors for research.
In the field of material science already some progress has been made.
A lighter compound that can be used in turbine blades for aircrafts has
been created. In the medical and physics research areas also interesting
discoveries have been made. One of those is the growth of crystals. Proteins
in the human body are responsible for a variety of biological functions,
such as the repair and build of tissues. Protein crystallography
helps understanding the structure of protein. On Earth, the growth of
crystal is influenced by gravity. However, in a microgravity environment
its influence is much smaller. This results in crystals growing to much
larger sizes than here on Earth. This makes the structure analysis much
easier and is useful in developing medicine for all kinds of diseases.
Another observation following from experiments in space is that what
we perceive as natural convection disappears. On Earth hot air naturally
flows up and cold air goes down. However, in a microgravity environment,
there is no up or down. Other forces now determine the movement
of the hot or cold gas or liquid. An example where this is shown is
the shape of a combustion flame. On Earth, the gases from the chemical
reaction of combustion are much hotter and rise. This makes the shape
of a flame more like a falling teardrop. In microgravity the hot gases are
not influenced by gravity anymore and the flame looks more like a ball.
At the moment, research regarding microgravity is still ongoing. With
the continued exploration of outer space, a better understanding of microgravity
and its effects is necessary. Not only in the ISS, but also in
drop towers on Earth, experiments take place. There are multiple drop
towers already in use around the world, the closest one being in Bremen.
Every year around 400 drop experiments are carried out there.
They even have a program that assists students with research projects
in the drop tower. But they are not the only one. So, if you want to find
out more about microgravity, make sure to contact one of the research
centers available and pitch your ideas! n
DE APPEL 17

TAKE A MINUTE
TO LOOK AT
THOSE WATCHES
PHOTOGRAPHY MICHIEL LOUWÉ
To accurately read time at any place, numerous small devices have been developed
over the last centuries. Starting roughly in the same era as our famous hero in
the seventeenth century, the clocks and watches have a rather long history which
results in the most beautiful technique on its scale. Engineering effort has gone
to various different mechanisms to let the user know precisely what time it is. This
has paid off twofold: mechanical mechanisms have reached high accuracies and
their appearance is simply magnificent. Thanks to Maaskant
Juweliers at Apeldoorn, we have taken a look
inside the clock and watch
world.
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24 DE APPEL
ASSOCIATION NEWS
IN THE PICTURE
THE LUSTRUM HAS BEGUN!
The Lustrum has finally begun! Newton has turned 55 years old, and
that is of course a reason to celebrate. Sadly, a lot of the activities
we would have had right around now were rescheduled due to corona.
Luckily though, the lustrum committee still had some awesome
things planned for now as we still wanted to celebrate on time
of course. With the lustrum opening kicking it all off, a great drink
behind the Horst was held with amazing weather! A fair bit of drinks
had been poured and a fire was lit, very much Olympic games style!
Everyone was seated as per the official guidelines, however this took
nothing away from the fun. A lot of people stayed the whole drink
from half past three to eight, but this seemed to be no time at all, as
the theme of the lustrum says “Time Flies” right? At the end a nice
J
song was sung with everyone there. The lustrum committee also baked
a huge apple pie for the Dies. With roughly 1.6 m2 of apple pie,
there was enough to go around and it was handed out in the Horst
canteen, people being guided to it with the green carpet as every year.
There was also a selection of merchandise arranged by the committee.
Three pieces were created, a clock, a LEGO apple and a pair of
custom pockies. Next to this, the lustrum committee has also set up
the lustrum radio, so that the lustrum cheer could be broadcasted to
everyone who is working at home! It is safe to say, despite the bad luck
we have had with this year’s celebration, we are still making the best
out of it and it is definitely showing!
24 DE APPEL

OPENING NEWTON ROOM
Since the summer holiday is over, the Newton Room has opened
once again for the members! We have coffee and free notebooks as
always, but there is a walking route and there can not be too many
people at once in the room. We are very happy to see you once more
in the Newton Room though, so please come and get a cup of coffee!
We are happy to have a chat as well of course, just make sure it is
not getting too cramped!
KICK-IN
With the new year starting, the Kick-In came along as always. New
students were welcomed to Enschede and shown around to the best
of the do-groups ability while the corona measures are still in play.
Such as all other events, the Kick-In was altered quite significantly
as well. Do-groups were still set up, this time by presenting themselves
with just videos, and they made sure the new students had a
great time in their first experiences in our city!
LUSTRUM RADIO
COMMITTEE INTEREST MARKET
With the corona measures, the committee interest market had to be
held a little bit differently than it normally would have been held.
This time we held the committee interest market outside of the
Horst, on which we were luckily enough greeted with some great
weather once again. A lot of committees were presenting themselves
to interested members and a lot of interested members were
there to sign up for the committees. All in all, the attendance was a
little lower than normally, but that is to be expected if most people
are working at home, but it was a good market nonetheless.
As was mentioned before, the lustrum committee has set up the
lustrum radio. The committee has made a whole set-up in Diepzat,
making it a temporary radio studio in which our members come and
make Radio for an hour each on Thursdays. People who signed up
could make radio the way they wanted for an hour long according
to a schedule made by the lustrum committee. This radio was going
on all Thursdays in October for six hours every time. The radio has
reached far and wide, taking over multiple association rooms in Enschede!
DE APPEL 25

ADVERTORIAL
NUCLEAR:
A SUSTAINABLE POWER
SOURCE FOR A
DECARBONIZED FUTURE
The scientific case for climate change is
overwhelming, immediate and undeniable
– the burning of fossil fuels has to stop. If
climate change is the biggest challenge
facing humanity, how can we quickly move to
a global energy supply that meets our needs
while remaining sustainable and protecting
the planet?
Every small action makes a difference, of course: recycle those cans;
walk instead of drive; cut down on plastic packaging; and produce less
waste, if possible. But will that be enough? Our hunger for energy continues
to rise, and not just in the most obvious ways of transport, heat
and light. After all, even an email has a carbon footprint, and something
needs to power the internet.
“We have to do everything possible to overcome this challenge, and we
have to do it now,” says Reinhard Hinterreither, CEO of ETC Nederland,
a company based in Almelo which designs and builds highly sophisticated
centrifuge systems for enriching uranium so it can be used as
nuclear fuel. “Only a mix of the different types of renewable energy
sources, plus nuclear energy, can help remediate the problem and give
us an achievable and sustainable energy supply. If we genuinely want
to get to zero CO2 emissions and completely decarbonize by 2050, there
isn’t any other way.”
But what happens when the uranium runs out? “Uranium is one of the
most prevalent elements in the earth’s crust, as common as tin or zinc”
says Hinterreither. “Also, the Japanese have already developed a method
for extracting it from sea water. If this proves cost-effective it would
provide almost limitless raw material.”
Delivering future demands while decarbonizing is not going to be easy.
“Can anyone predict when the human race’s demand for power will
actually fall?” asks Hinterreither. “Our industrial processes need huge
amounts of energy. If we want to continue to produce the steel and concrete
that underpin our engineering projects without burning fossil
fuels, we need nuclear power. Looking at the technologies that we have
available today, if we are serious about achieving net carbon zero by
2050, there is no other option but to embrace nuclear power as part of
an energy mix that drives and sustains a cleaner world.”
Renewable energy sources on their own are not going to meet our
needs. Europe, and the Netherlands in particular, simply doesn’t have
enough room for the amount of infrastructure needed to produce sufficient
wind and solar energy. It also can’t afford a 40cm rise in sea
levels. “Any other solution has a massive infrastructure commitment
that would take decades, which is time we don’t have” comments Hinterreither.
Instead, he points to advances being made in nuclear technology which
address the issues that have seen nuclear energy’s popularity diminish
over the last decade. New Generation IV reactors are being developed
that are inherently safe. Huge investments are being made into techniques
for using and re-using nuclear materials to produce more electricity.

MICRO HUISDIEREN
KLEIN FORMAAT, GROTE GEVOLGEN
DOOR SABINE VAN DER WERFF
Puppy’s, kittens, veulentjes, kalfjes, biggetjes… Zouden ze maar voor altijd zo klein en schattig
kunnen blijven! U vraagt, wij draaien, moet de (huis)dierfokkerij gedacht hebben. Inmiddels zijn
miniatuurdieren redelijk makkelijk te verkrijgen, van klein tot heel klein en alles daartussenin.
Ze staan fantastisch op je instagrampagina, en zo’n wollig kopje met guitige oogjes is een leuke
accessoire in je handtas. Maar hoe schattig en lief is dat nou eigenlijk echt? Helaas blijkt het
allemaal toch iets minder rooskleurig, want kleine dieren komen met grote gevolgen.
DE APPEL 27

HOE KLEIN?
Dwerg, toy, mini, micro, miniatuur, teacup, pocket, de naamgevingen
voor kleine dieren zijn eindeloos. Dat maakt het soms best verwarrend,
want geen van deze benamingen is “officieel”. Het zegt dan ook helemaal
niks over hoe groot een dier uiteindelijk kan worden, het is een willekeurige
term die de fokker zelf gebruikt om zijn huisdieren te verkopen.
Het kleinste erkende hondenras door de FCI, de internationale rashondenorganisatie,
is de chihuahua. Chihuahua’s horen volgens de rasstandaard
tussen de 1 en 3 kg te wegen, en zijn ongeveer tussen de 15 en
22 centimeter groot. Het kleinste kattenras dat is erkend door de FNK,
de Federatie Nederlandse Kattenverenigingen, is de singapura, die niet
zwaarder wordt dan 4 kg.
Dat dit de twee kleinste erkende rassen
zijn, betekent echter niet dat er geen
kleinere dieren worden gefokt.
Vanwege alle risico’s die deze
kleine afmetingen met
zich meebrengen wordt
het ten zeerste afgekeurd
door dierenartsen
en de
internationale
en nationale
overkoepelende
ras- en
fokverenigingen,
maar
het is daar bovenop
ook nog eens verboden. De
NVWA is er erg duidelijk over:
de fokker moet ervoor zorgen dat het
ouderdier geen schadelijke, uiterlijke kenmerken
aan de nakomelingen doorgeeft.
Om een idee te geven hoe klein zulke dieren nou eigenlijk zijn, maakt
een groep onderzoekers een treffende vergelijking. Waar een gemiddelde
hond zo rond de 30 kilo weegt, wegen veel kleine hondjes minder
dan 5 kilo of zelfs minder dan 1 kilo. Zouden we dezelfde verhouding
aanhouden voor mensen, dan hebben we het over volwassen mensen
van 2 tot 10 kilo.
HOE FOK JE ZO’N KLEIN DIER?
Dat het niet gewenst of zelfs niet toegestaan is om zulke kleine dieren
te fokken, zal sommige, discutabele, fokkers een worst wezen. Dit soort
fokkers worden broodfokkers genoemd: fokkers die hun brood verdienen
met dieren fokken. Dit gebeurt vaak onder trieste omstandigheden,
waarbij de dieren niet de zorg krijgen die ze verdienen, omdat teveel
kosten met zich meebrengt en de winst dus afneemt. Mensen zijn bereid
om grof te betalen voor een harig bolletje schattigheid, en voor broodfokkers
komt dierenwelzijn dus niet op de eerste plaats.
De meeste miniatuurdieren worden gefokt uit rassen die ‘van nature’
al niet groot zijn, of kruisingen van zulke rassen, zoals maltezers, keeshondjes
en poedels bij honden, of hangbuikzwijntjes bij varkens. Om dan
het gewenste formaat te krijgen, worden de kleinste dieren weer geselecteerd
om verder mee te fokken. Dit selectief fokken is niet iets onbekends,
vaak wordt het gedaan om een ras te verbeteren
en om de goede, gewenste eigenschappen
van een dier door te geven
aan de
volgende
generatie.
Dit werkt
echter alleen
als het
verstandig
ingezet
wordt door
iemand die
oog heeft voor
het algehele
dierenwelzijn. En
daar zit nu net het
probleem.
De kleinste dieren uit een
nest zijn vaak ook de zwakste,
minst ontwikkelde dieren.
Met goede zorg en een hoop liefde
komt het met deze nakomelingen in normale
omstandigheden vaak wel goed, maar wanneer
een fokker ervoor kiest om twee zwakkere dieren te
gebruiken om te fokken, kan je voor nare verrassingen komen te staan.
Soms zijn nakomelingen simpelweg zwak door een tekort aan voedingsstoffen,
maar het gebeurt ook dat er een afwijking of ziekte aan ten
grondslag ligt. Als je met zulke afwijkingen verder fokt, wordt de gezondheid
van het diertje er niet beter op, met alle vervelende gevolgen
van dien.
GEZONDHEID EN ANDERE PROBLEMEN
Die vervelende gevolgen en gezondheidsproblemen, dat zijn er nogal
wat, en ze zijn niet mals. Een van de grootste problemen is dat vooral
28 DE APPEL

het skelet verkleind wordt, maar dat de zachte weefsels niet evenredig
kleiner worden. Een aantal gevolgen zijn onder anderen dat de oogjes
uitpuilen, er ademhalingsproblemen zijn en dat de hersenen te groot
zijn voor de schedel, Dit laatste zorgt bij honden in veel gevallen voor
twee aandoeningen genaamd chiari malformatie en syringomyelie: de
hersenen worden weggedrukt, blokkeren het ruggenmerg en leiden uiteindelijk
tot hoofdpijn, waarbij sommige hondjes zelfs agressief worden
of het uitgillen van de pijn.
Nog een probleem van het verkleinen van het skelet is simpelweg dat de
botjes alsmaar kleiner worden, waardoor ze sneller breken. Hierdoor is
spelen met (grotere) soortgenoten niet mogelijk, ze zijn immers extreem
kwetsbaar. Nog schrijnender: het is al meerdere malen gebeurd dat iemand
per ongeluk bovenop zijn eigen hondje is gaan staan, vaak met
(voor de hond) fatale afloop.
Ook bij katten zijn dwergvarianten in trek, een goed en bekend voorbeeld
is de Munchkin kat. Deze variant is met zijn korte pootjes en “normale”
lichaam het beste te omschrijven als een teckel-kat. Met dit opvallende
uiterlijk ziet de kat er best schattig uit, en hij wordt er dan ook
doelbewust op gefokt. De korte poten van de Munchkin zijn echter te
wijten aan een genetische afwijking, die naast dwerggroei ook veel andere
gezondheidsproblemen met zich meebrengt, zoals een afwijkende
ruggengraat en vervormende kaken. Daarnaast zijn ze ook niet goed in
staat om te rennen of te springen, waardoor ze enorm beperkt worden
in hun “normale” kattengedrag. Ook andere rassen kunnen in dwergformaat
voorkomen, vaak als gevolg van een afwijking. Net als met honden
wordt het fokken met dit soort mutaties sterk afgekeurd door de meeste
organisaties.
EEN VARKEN IN JE HUIS
Naast de standaard hond en kat, zijn er ook nog genoeg andere dieren
die veel leuker schijnen te zijn als ze klein zijn. Bonus: je kan ze dan
ook als huisdier houden! De miniatuurkoe en het mini-varken zijn geen
uitzonderingen, maar er zijn nog genoeg andere dwerg-varianten van
(boerderij)dieren te bedenken. Hoewel er minder te vinden is over de
gezondheidsproblemen van deze dieren, is het niet onwaarschijnlijk dat
ook zij niet vrij van gebreken zijn.
Het klinkt misschien redelijk logisch, maar een varken of koe als huisdier
is niet voor iedereen weggelegd, je moet goed bedenken waar je
aan begint en of dat überhaupt wel een verstandige beslissing is. Maar
Google op “mini koe” en het eerste wat je ziet is de kop “Dit wil je hebben:
Een fluffy mini-koe als huisdier” op een “online lifestyle magazine voor
de twenty something vrouw die alles uit het leven wil halen”. Over het
algemeen niet het publiek dat kennis heeft over het houden van dergelijke
dieren. Het artikel bejubelt hoe schattig de koetjes wel niet zijn, met
vervolgens de uitleg waar je er een kan aanschaffen. De enige disclaimer
is dat je ze waarschijnlijk niet in je appartementje moet houden.
Het is een illustratie van het soort onwetendheid en onkunde dat vaak
leidt tot problematisch gedrag van dit soort huisdieren. Minivarkens en
-koeien zijn nog steeds varkens en koeien, en die zijn niet gemaakt om in
een huiskamer te wonen, ze hebben behoefte aan contact met soortgenoten
en buitenruimte, om maar een voorbeeld te noemen. “Vervelende”
minivarkens als gevolg van verkeerde huisvesting en opvoeding zijn
geen uitzondering, er zijn zelfs speciale varkenstehuizen om dit soort
gevallen op te vangen.
Dit is nog maar een korte opsomming van alles wat er mis kan zijn of
mis kan gaan met miniatuurdieren, de lijst is immens. En natuurlijk, het
is niet gezegd dat grotere rassen dan wel volledig zonder gebreken zijn,
want ook die kennen hun eigen problemen. Dat neemt echter niet weg
dat fokken voor extremen tot ontzettend sneue situaties kan leiden voor
DE APPEL 29

de dieren in kwestie. Maar niet alleen de dieren zijn de dupe van deze
trend, ook voor mensen kan het soms vervelend uitpakken.
OPLICHTING
Extreem kleine dieren zijn populair, mede door social media accounts en
beroemdheden die graag laten zien hoe schattig zo’n dier is. Door deze
grote interesse kunnen de fokkers veel geld vragen, er zijn teacup hondjes
die verkocht worden voor omgerekend tot wel €7500,-. Maar met zo’n
prijs ben je nog niet verzekerd van een gezonde en gezellige hond.
Met alle risico’s voor de gezondheid van de mini-dieren kan een koper
voor vervelende verrassingen komen te staan. Een puppy laat misschien
nog geen problemen zien, maar zodra ze ouder worden kunnen de gebreken
opstapelen, en de rekeningen van de dierenarts ook. Daar komt
bovenop dat broodfokkers de dieren vaak onder valse voorwendselen te
jong verkopen, omdat ze dan kleiner zijn. Puppy’s en kittens mogen in
Nederland vanaf 7 weken het nest uit. Een dier dat eerder het nest verlaat
is minder goed gesocialiseerd en mist cruciale vaardigheden in het
omgaan met soortgenoten.
De industrie achter zulke dieren is niet heel transparant en waarschijnlijk
ook niet heel gezond. Websites die vanuit bijvoorbeeld Korea teacup
puppy’s aanbieden zijn zo te vinden, en zijn bereid het hondje naar je op
te sturen. Ze geven ook een gezondheidsgarantie van een jaar, op een
aantal aandoeningen die leiden tot de dood, hartafwijkingen en een aantal
virussen. Mocht het hondje nu een onbehandelbare aandoening hebben
of daaraan overlijden, dan is het bedrijf bereid je een nieuw beestje
op te sturen van hetzelfde geslacht, ras en kwaliteit als waarvoor je had
betaald. Alsof je dieren zo kan inruilen.
Mocht alles nu goed zijn gegaan en je een leuk huisdier in je hart hebben
gesloten, dan is er nog een mogelijke uitdaging: het dier blijkt helemaal
geen mini-huisdier te zijn! Je zal niet de eerste zijn met een volledig volgroeid
varken in huis, terwijl je in de veronderstelling was dat het voor
altijd het formaat van een biggetje zou blijven. En dat is toch vervelend.
GOED NIEUWS!
Gelukkig is er niet alleen maar ellende. Steeds meer mensen worden
zich bewust van de grote problemen die bij heel kleine dieren komen
kijken, en van broodfokkers in het algemeen. Dit is mede door dierenartsen,
dierenwelzijnsorganisaties en ras- en fokverenigingen die zich
nadrukkelijk uitspreken tegen dit soort praktijken.
Ook verkoopplatforms nemen hun verantwoordelijkheid, zo heeft de
Duitse eBay de verkoop van alle dieren die volgens de Duitse wet onder
het ‘martelfokken’ vallen, verboden. Marktplaats heeft zo’n verbod nog
niet, maar het is wel mogelijk om malafide advertenties te melden. Ook
neemt de NVWA stappen, de opsporingscapaciteit voor broodfokkers is
in 2020 verdubbeld naar 10 fte.
En natuurlijk zijn er ook heel veel fokkers die wel hun verantwoordelijkheid
nemen. Ze kijken naar waar het ras te verbeteren is, waar de dieren
baat bij hebben en zorgen dat ze een gezond en gelukkig leven tegemoet
gaan.
Dat er nog zoveel interesse is in schattige maar ongezond kleine dieren,
is ontzettend verdrietig, vooral voor de dieren zelf. Het beste advies is
om ze simpelweg niet te kopen, want door zulke dieren aan te schaffen
wordt de industrie in stand gehouden. Dat neemt niet weg dat je nooit
meer een huisdier mag nemen, want een dier in huis is vooral ontzettend
gezellig! Maar doe het dan wel verstandig; denk goed na over wat
je een dier kan en wil bieden, lees je in over een huisdier adopteren of
kopen en doe een beetje onderzoek naar het ras en de fokker. Dat is voor
jou een kleine moeite, maar daarmee doe je je dieren een groot plezier! a
30 DE APPEL

COLUMN
HUGO WESSELINK
CAMPUS QUARANTAINE
Er zijn in het verleden een flink aantal experimenten geweest
waarvan men achteraf vond dat een strengere ethische
commissie niet misplaatst zou zijn geweest. Echter zullen
de vlagvoerders van deze experimenten, er vanuit gaande
dat Rutger Bregman gelijk had en dat de mens goed is, niet
hebben gestreefd naar deze resultaten. Bij deze hang ik dan
ook een kleine disclaimer aan deze column. Mocht het hier
beschreven hersenspinsel worden uitgevoerd, maar achteraf
niet heel hoog scoren op het ethisch gebied, dan was
dat niet zo bedoeld.
Door de steeds veranderende maatregelen
van Mark, Jaap en Hugo verandert ook
steeds onze lockdown situatie. Eerst
was het een intelligente lockdown,
daarna mocht er weer een hoop en
nu zijn we al weer verzeild geraakt in
een nieuwe (gedeeltelijke) lockdown.
Toch heeft dit coronatrio het nog niet
één keer gehad over de lockdown die
ik graag zou willen invoeren. Ik wil het
namelijk hebben over een nieuwe vorm van
quarantaine, de campus quarantaine. Veel studenten
balen van hun ingeperkte vrijheid en snakken
naar het verleden waar huisfeesten, sporten en onbeperkt
sociaal contact de norm waren. Nu begrijpen we heus wel
dat dit met de huidige omstandigheden niet mogelijk is en
we onze verantwoordelijkheid gewoon maar moeten nemen,
maar wat als dit gecombineerd zou kunnen worden? Een
oase van vrijheid, sociale contacten en als kers op de taart:
een flinke portie verantwoordelijkheid. De campus quarantaine
begint met een periode van drie weken, waarin iedere
campusbewoner de kans krijgt om deel te nemen aan het
sociaal experiment. Deze uitnodiging aannemen dan wel afwijzen
is geheel vrijwillig, echter wordt er bij verwerping van
het aanbod vriendelijk doch dringend verzocht een nieuwe
woning buiten de campus te zoeken. U wilde immers niet
meedoen.
Na deze initiële periode kan fase twee van start gaan: de
campus gaat in lockdown. De vrijheidsoase wordt gecreëerd,
maar ook direct afgebakend. Bewoners mogen namelijk de
campus niet meer af en buitenstaanders mogen er niet meer
op. Dit recht behoort enkel tot de toevoer van de Coop, de
Vestingbar, Diepzat en andere vergelijkbare etablissementen.
Gezien geen enkele docent nu de
campus meer op mag, zullen ook je laatste
analoge colleges zich verplaatsen naar
Teams of Discord. Je ouders, de kapper of
de markt bezoeken is ook verleden tijd
en vervangen voor hetgeen waar je zo
naar snakte: de sociale interactie van
de pre-corona campus. Je mag weer
onbeperkt sporten in teamverband,
drie huisfeesten in één weekend afwerken
en net zo lang aan de bar blijven zitten
totdat het TL licht aangaat en piano man
afgelopen is. Zo lang het maar op de campus is.
Mocht je onverwachts een griepje krijgen en naar de IC
moeten voor een beademingsapparaat, helaas. Het is te hopen
dat je jong en vitaal genoeg bent en dat het met een paar
dagen goed uitzieken weer over is.
Met de campusquarantaine is in één klap de speelruimte
terug waar zo naar wordt gesnakt. Daar bovenop wordt er
geen enkel zorgstelsel overbelast, omdat er simpelweg géén
gebruik van zal worden gemaakt. Het is een perfecte balans
tussen vrijheid en verantwoordelijkheid, doordat de top van
studerend Nederland zichzelf afsluit van de buitenwereld en
zich schuilhoudt in zijn eigen oase. Een daadwerkelijk intelligente
lockdown. HW
DE APPEL 31

THE LITTLE WAR
BUILDING WITH LEGO
BY FAUSTO VISSER
Since the first general purpose processor set free from the
R&D development tract and made into a consumer product
the race was on. The race for ever faster, cheaper,
more efficient and more versatile forms
of compute was born. However, around
the start of this decade it was clear who was
leading the race. With Intel capturing more than
70% of the marketshare in the processor market and
even more than that with the laptop and server divisions.
What Intel had been doing since 2007, and quite succesfully at that was
their tick-tock engineering strategy. Every year an new line of processors
would be released, however not every year was the same. A tock
was a change and redesign of the micro architecture which mostly allowed
for streamlining of the innerworkings of the processor and the
implementation of new features. The following step, a Tick, introduces
a new fabrication process that would allow the node size to be shrunk
down. What this essentially means is that the same physical features
on the processor can be packaged in a smaller physical area. This by
decreasing the nanoscopic disctances between the nodes, such as in
2010 when moving from the Nephalem architecture (42nm) to Westmere
(32nm). Decreasing this distance means there is less length to be travelled
within the CPU which generally results in less powerconsumption
for the same performance. An added benefit is that the die (piece of silicon
in the cpu) can now either be made smaller such that more processors
can be made from the same size wafer. Or the die size can be kept
the same but performance will be greatly improved.
Until about 2015 this strategy worked swimmingly, with the update of
the skylake microarchitecture on the existing 14 nm production process.
This would be the last time that the tick-tock bell had rung per
usual. For the next step would be the move to a 10nm production process.
But Intel had and has quite some problems with making this step .
In the last five years only a few chips have come from Intel on the 10 nm
process but most are still made on 14nm.
Meanwhile over at AMD things had been quite rough. Their last processor
that could really compete with the offerings from Intel had been in
the form of the AMD phenom II X4 in 2008. And even that was for the
bit more budget concerned pc builder, on the high end Intel held all the
cards with their i7 processors. After that came some marginal succes
and a few big failures. Most likely inspired by the succesfull quad core
designs of Intel, Amd focussed on the multicore aspect of the processors.
With their new generation of bulldozer cpu’s launched in 2011 they
promised high performance numbers with low power consumption. Dis-
32 DE APPEL

CORE 0 CORE 1
CORE 4 CORE 5
CORE 2
CORE 3
CORE 6
CORE 7
CORE 8 CORE 9
CORE 12 CORE 13
CORE 10
CORE 11
CORE 14
CORE 15
appointingly this generation could only come close to the competition
from Intel, which was to top it off even cheaper. Small pickings were had
by AMD in the desktop APU market. These were small computers with
considerable graphics performance for their size, which a nice integration
tactic as the graphics cards branch of the company had been doing
quite well. In these years most of the profits of AMD originated from
making chips akin to their APU’s for the console market. AMD chips
were found in the XBOX one, playstation 4, playstation 4 pro, XBOX one
S, XBOX one X and the playstation 5.
In 2017 AMD came with the launch of RYZEN, which would mark the
beginning of the resurgence for AMD. With the first generation of this
concept AMD was able to provide more performance, especially in multi
core applications, than intel in their offering while undercutting them
on pricing. How they managed this was by completely changing the way
they produce processors.
MONOLITHIC DESIGN
Virtually all processors are made by engineering a single piece of silicon,
the so called die. This includes the 2 to typically 4 cores, the low
level cache, on board graphics and the I/O. Incorporating all these parts
on single piece of silicon requires quite some engineering, but has certainly
been proven as the go-to method. However this approach requires
a different design and layout for every processor that is produced.
These differences in design also impact the production, as every design
has to be produced individually. This model of production is called the
monolithic design aproach.
CHIPLET APPROACH
Instead of making different pieces of silicon for each and every chip
AMD went down a different path in 2017. Their base unit became a computing
block with four cores, this is essentially their smallest lego block
with which they build virtually all their processors. A pair of these is
installed on one die (piece of silicon) where they share things like cache
and other things, this is the basic unit and called a CCD. Essentially
meaning an eight core processor is the smallest one made. But in the
whole line up there are 6, 8, 12, 16, 24 and 32 core processors. These
are all still built from those eight core dies, so a 16 core processor is
formed by combining two CCD’s that each contain eight cores. This can
be further extended for a 32 core processor by combining four of these
units. But now comes the ingenius part. With any production process
there are rejected parts, that is simply an inevitabilty. Especially in the
semi conductor industry a considerable part of the produced chips can
be rejected due to faults. Generally these faults are localised an thus
will have one or two cores that are faulty. So the 6 core processors are
made by taking the partial rejected eight core blocks, disabling the two
faulty cores which then can have a productive life as a six core processor.
The same is done for the 4 core unit where half of the cores were
not working etc. Meaning the statistical yields of the production process
are part of the strategy to create a line up varying from budget
processors all the way to enthausiast and server products. Compared
to the monolithic approach this makes sense for a larger number of
cores as the risk of a completely failed product is much lower.
The last contributing factor for the resurgence of AMD is that because
their process naturally accounts for failures they have been able to
more quickly move to a smaller process. In 2017 they started on 14nm,
12nm in 2018 and in 2020 they moved to all the way down to 7nm, while
Intel is still on 14nm. This leap in technology in a market that had been
dominated by one party means that active competition has resumed
after a lull of about 12 years. In the end this should only mean faster
technological progress from both sides where hopefully the consumers
and new siences enable by faster compute will have the pickings. k
DE APPEL 33

ADVERTORIAL
COMBINED EXPERTISE IN MOTION CONTROL, ELECTRONICS, SOFTWARE AND
MECHATRONICS UNIQUE IN EUROPE
NTS’ KNOWHOW OF
MECHATRONIC PRINT
SYSTEMS CONSIDERABLY
SHORTENS CUSTOMERS’
TIME-TO-MARKET
System architect Mike Curvers (47) develops printing systems at
NTS. Twenty years ago, he started at a predecessor of NTS. He
saw his professional field change: mechanical machines became
mechatronic, motion control continued to become more important
and the demand for printing flexible, customised series continued
to grow. Moreover, technologies like printing reliefs and Additive
Manufacturing entered the market. The know-how NTS has in the
field of customized printers is unique in the market. “Our knowledge
and experience in the field of motion control, electronics and
mechatronics cannot be found at any other company. That helps our
customers to considerably shorten their time-to-market.”
Mike was already interested in technology at a very early age. During
his study he found electronics especially appealing. In practice he discovered
that he was mainly fascinated by engines and propulsion That is
why Mike chose to start at Te Strake, one of NTS’ predecessors.
“That was twenty years ago,” Mike says: “and now I still work here. In
that time a lot has changed, the company has professionalised a great
deal. Although we were already a forerunner back then when it came
to our machines for textile printing for instance. That was a very innovative
product.”
UNDERSTANDING EXACTLY WHAT HAPPENS
“Back then those machines were entirely mechanical. At a later moment
in time they became mechatronic: a combination between electronics,
software and mechanics. The textile printer is an example of an extensive
project that I have worked on. It is a system printer, motion control
in this case is very complex, the ink needs to end up in the exact right
position. I want to be able to understand what happens exactly and I
want to see that it works.”
FROM CUSTOMER QUESTION TO PROJECT PLAN
AND CONCEPT
“Recently we received a question from a customer that wanted to develop
a bar in which printheads needed to be integrated. At such a moment
we demonstrate the customer what we have already done before
and what our competences are. The customer was enthusiastic, we showed
him what he wanted to see and he chose to work with NTS. After he
had sent us his requirements, we made a project proposal and then you
translate it in a project plan and a concept.”
“We are now working on the next step. We are going to further investigate
the things we have and the aspects that are difficult to develop or
produce. In this process we look at whether it is possible to manufacture
it and whether it is possible to clean all components. The customer does
not have the knowhow to do that himself.”
ROBOTS KULICKE & SOFFA ARE STILL BEING
BUILT
“Another example of a system that I have worked on in the past and that
is still in production, is a robot that we developed for Kulicke & Soffa.

ADVERTORIAL
These robots among others are used for assembling circuit boards. I
started developing these robots some 17 or 18 years ago and they are
still being used. The robots of course are continuously being updated
by NTS’ Assembly division. When a certain component is not available
for instance an alternative is looked for. The fact that the robots are still
being used, is really nice.”
“Sometimes we also develop machines that eventually do not obtain the
results that the customer expected. Take the inkjet printer for textile
as an example. Seen from a technical perspective the machine worked
perfectly, but from a commercial perspective the inkjet printhead was
simply too expensive. That is something you see more often in the inkjet
print market: some projects are really innovative which does not always
make it easy to predict the commercial viability.”
BEST PROJECT EVER: PRINTER OF 800 KILOS
WITH HIGH PRECISION PRINTHEADS
“The best project I have ever worked on is a very large printer for Agfa.
It is a large industrial printer with a print system that weighs 800 kilos
and has 64 printheads that need to move with an accuracy of 10 micrometre.
We were mainly responsible for the motion control and electronics.
That was really, very nice. It was even patented.”
“Agfa has a sound knowledge of inkjet but does not have enough expertise
of this type of motion control. We have developed the printer
together with three parties. A lot of the testing took place in Germany.
That was a very nice period, the collaboration was very good. During
daytime we worked hard and, in the evenings, we went out to dinner
and explored the environment. It was challenging, educational and fun.”
“In the end about 30 of this type of machines have been manufactured
and I am very proud of it. The machines among others are used to print
commercial posters. The well-known glass display posters that you for
instance can see in subway stations in Great-Britain. Eventually the
image quality of the inkjet printer was better than an offset image. For
that time, it was really unique.”
INKJET OFFERS GREAT FLEXIBILITY
“The advantage of inkjet over offset is that it offers you great flexibility.
It is extremely suited for printing small series or limited editions. You
can also apply special effects, like printing layers, fast marketing campaigns
where you print relief on packaging, printing a wooden pattern
on boards, printing panels and so on. It offers you a wide range of possibilities.”
continuously greater variety of materials are being printed.”
PRINTING ON PRODUCTS
“Inkjet printing is also evolving. One of the new developments in the
field of inkjet is printing directly on the final product. Think of plastic
bottles. We print directly on the bottle and because of this you do not
need to use a plastic wrap. By doing so, you reduce the required number
of activities and the logistics, which reduces your footprint and makes
it better for the environment. Furthermore, personalising products is
something you see more and more often.”
KNOWLEDGE NTS HAS OF MOTION AND PRINT
SYSTEMS IS UNIQUE IN EUROPE
“What NTS does in the field of motion and print systems and the experience
we have in this field is unique in Europe. Not a single other
company has the expertise that we have in the combination of motion
control, electronics, software and mechatronics. We do not sell products
of our own. Our services consist of helping our customers design and
develop customised print systems and parts of these systems in order
to manufacture them in series.”
NOT A SINGLE OTHER COMPANY KNOWS ALL
PARTS AND CAN ALSO MANUFACTURE THEM
“There are a lot of other companies with a specialism in specific parts
but there isn’t a single other company that has knowledge of all parts
and that can also manufacture those parts. When NTS would not have
had these competencies, a considerable number of the print systems
that are currently on the market, simply would not have existed.”
EXPERTISE NTS SHORTENS TIME-TO-MARKET
CUSTOMER
“Moreover, our expertise helps customers to develop and manufacture
the machine they have in mind in a much shorter period of time. They
could do it themselves and hire people for it but the enormous advantage
NTS offers, is that we don’t have to go through the learning curve. We
already have the experience we need in the field of deposition systems
and in the field of manufacturing and assembly.”
EVER SMALLER SERIES
“The wish to be able to be flexible and print small customised series is
something you hear a lot in the market. You don’t see a lot of large series
anymore. Certainly not in Dutch industry. It is all about small series and
large flexibility. Products generally have a continuously shorter lifespan.
Think of potato chips, in the past you could choose between a natural
or sweet pepper flavour, now you continuously have new flavours.
These new products repeatedly require new packaging.”
3D PRINTING IS ON THE RISE
“Another trend you see in the market is 3D printing. Initially it was
mainly used for prototyping purposes but now more and more often it
is used for printing the final product. It also concerns products that cannot
be produced in one piece by using another production technique, a
chess piece for example. Additive Manufacturing is rapidly developing. A

THESIS ARTICLE
TEMPERATURE
AND STRAIN RATE
DEPENDENCE
FOR END-LOADED
UNIDIRECTIONAL
GLASS-POLYPROPYLENE
COMPOSITES
BY ROLAND GUIJS
Composites have seen a rapid increase in usage for various applications. The combination of
lightweight and a good mechanical properties is an often-praised characteristic. Whereas
the latter is related to the usage of high-strength fiber in the composite, such as carbon or
glass, does the polymer matrix offer other great opportunities for the possible applications of
composites. Its high degree of freedom and suitability for mass-production with, for example
injection-moulding opens up endless new possibilities. This leads to, among others, new shapes
and significant material reductions. Based on all of these advantages, composites become
more and more of an alternative for conventional materials. Due to its rapid emerge in both
science and the industry, the available knowledge on it is rather limited. The fact that there
are numerous variations and types of composites, all with their own (mechanical) properties,
increases the lack of insight in composite behavior.
36 DE APPEL

LEFT, SCHEMATIC REPRESENTATION OF THE RELATION BETWEEN THE YIELD STRESS
AND APPLIED STRAIN RATE FOR A VISCOELASTIC MATERIAL. RIGHT, SCHEMATIC
REPRESENTATION OF THE RELATION BETWEEN THE YIELD STRESS AND TEMPERATURE
FOR A VISCOELASTIC MATERIAL.
A mechanical property of composites of which is typically less known
is its compressive behavior. It is generally considered that the tensile
properties of a composite are superior to its compressive properties,
which is mainly related to the fact that the fibers used have good tensile
properties, but are sensitive in compression, for example because
of buckling. Due to the inhomogeneous structure of the composites,
performing qualitative research is impeded, mainly because of practical
reasons. The fact that composites are highly sensitive to their production
process, and hence their properties, makes this even more complicated.
For this research, a testing procedure based on end-loading
is used. Multiple tests at different strain rates and temperatures will
be performed, to establish a potential relation among these and the
compressive properties.
Due to the presence of the matrix and results from other research, the
hypothesis is formed that the composite will behave according to a
viscoelastic nature, just as the pure polymer would do. In this particular
case, a polypropylene polymer is used as comparison. If the hypothesis
would be true, it would mean that the available knowledge on viscoelastic
behavior of polymers could be applied to (unidirectional) composites
under a compressive load, which would significantly increase the available
knowledge and insight. Typical for polymers is their behavior over
time, of which delayed yielding is a typical phenomenon. In practice
this means that even at an applied stress below the yield stress of the
material, it can still fail, and sooner than expected. During for example
creep tests this phenomenon is exhibited. In such a creep test, typically
three stages of deformation can be distinguished. In the primary
phase, the viscoelastic phase, the rate of deformation decreases in time.
Afterwards, the material enters the secondary phase, which is characterized
by a constant strain rate. This is caused by the fact that the
applied stress matches the chain mobility in the polymer, resulting in
the constant creep rate. Eventually the strain rate will increase again,
ultimately resulting in failure of the specimen.
The delayed yielding described above is related to the applied stress,
which is described by Sherby-Dorn. In order for the chain mobility to
match a higher applied stress, an elevated chain mobility is required,
which will eventually result in a quicker failure of the material. Consequently,
with an increasing applied stress, the time-to-failure will
decrease, but the engineering strain will remain the same. When the
strain rate is plotted against the engineering strain for various stresses,
a so called Sherby-Dorn plot is created. Typically, this figure consists
of multiple convex lines, oriented vertically to each other. This convex
shape is characterizing for an unstable system, where at a strain rate
higher than the minimum strain rate, the strain rate will increase with
the strain, leading to an acceleration of the total strain of the material.
When these minimum strain rates are plotted for their applied stress
versus the log of the plastic flow rate, it can be noted that they are on a
straight line. On the same line, the yield stresses for samples tested at
various strain rates, will be as well. This corresponds with the theory
posed above, where the yield point can be regarded as the stresss level
where the macroscopic strain rate of the material matches the applied
strain rate. Based on this relation, according to Bauwens-Crowet et al.,
it can be regarded that during secondary creep the stress dependence
of the flow rate follows the same trend as the strain rate dependence of
the yield stress in a tensile test. Consequently, the stress dependence of
the flow rate can be quantified.
This is done in the Eyring’s activated flow theory, which depends on
both the temperature and the stress:
Other variables are the activation energy, Boltzmann’s constant and the
activation volume. The first term, also known as the Arrhenius term,
covers the temperature effects, whereas the sine hyperbolic covers the
plastic flow rate. Under isothermal conditions and with a constant applied
strain rate, this equation can be simplified to the following equation:
DE APPEL 37

YIELD STRESS IN MPA VERSUS THE TESTING TEMPERATURE, TESTED WITH THE PURE END
LOADING METHOD.
This linear relation can be applied for single deformation behavior, typically
intra-lamellar. It expresses the relation between the yield stress
of a polymer and the logarithm of the applied strain rate. However, composites
often exhibit multiple deformation behaviors; an α -phase in
the plies, intra-lamellar, and a β-phase on the interfaces between the
plies, the inter-lamellar. At high temperatures or low strain rates, intralamellar
deformation is the dominant type to determine the yield stress,
whereas at lower temperatures or higher strain rates, inter-lamellar deformation
is dominantly present. Since these deformations act in parallel,
they can be described according to the principle of the stress additive,
resulting in the modified Ree-Eyring equation. For higher stresses,
this can be written as follows:
FAILURE OF SAMPLES, LEFT -20 C AND RIGHT 110 C, BOTH TESTED WITH PURE END
LOADING.
38 DE APPEL

MICROSCOPY IMAGE OF A TESTED SAMPLE, TESTED AT ROOM TEMPERATURE.
This equation describes the contribution of both the strain rate (I) as
well as the temperature (II) dependence of the yield stress. When this
trend is modelled, a line with a characteristic sharp bend can be recognized,
as seen in the figure. This bend separates the α-phase is dominant
and where both the α-phase and β-phase contribute. At a constant
temperature and increasing strain rate, the true yield stress will increase,
whereas with a constant strain rate and increasing temperature,
the true yield stress will decrease. This is typical for a viscoelastic material,
such as polypropylene, and research shows the same behavior for
glass-polypropylene (GPP) composites in tension.
To validate whether this same behavior can be regarded in a compressive
load state, multiple tests have been performed. As testing method,
a method based on pure loading and comparable with ASTM D695 is
used. To this extent, small, cubic samples with a 3.77 mm thickness will
be used. Crucial in the production phase of these samples is the planparallelism,
to obtain the required accuracy during testing. A deviation
of on average 21 micron was established.
With this method, multiple tests were performed, with sample sets
of five. The temperature was varied between -20 deg. C and 110 deg. C,
and the strain rate between 10^-5 and 10^-2 /s. This resulted in figures
comparable to the ones which were expected based on the modified
Ree-Eyring equation. An interesting observation during the test was
the fact that with increasing strain rates or decreasing temperatures,
the deviation between the multiple samples in a single set increased.
The temperature effect can be related to the fact that with increasing
temperature, the ductility of a material increases. Consequently, at low
temperatures the material tends to behave more brittle, increasing its
sensitivity for for example stress concentrations. Stress concentrations
can be an initiator for sample failure, which could explain the increased
standard deviation. Furthermore, the samples tested at elevated temperatures
exhibited little exterior damage after failure, whereas samples
tested at lower temperatures often split or had excessive damage.
For the tests with different constant strain speeds, a similar trend can
be recognized, as mentioned above. At higher testing rates, the deviation
among the samples tends to increase. Similarly, the damage to the
sample after failure is much more excessive compared to the samples
tested at lower strain rates. This can be related to the fact that at elevated
strain rates, the sensitivity for local defects and stress concentrations
in the material is increased.
When a close look is taken at a sample after failure, interesting observations
can be done. In the figure, a sample tested at room temperature
at a strain rate of 10^-3 can be seen. Approximately ¾ of the sample has
been removed, after it was embedded in an epoxy. Clearly, the fibers can
be recognized in the picture. The elliptic shapes which can be regarded
are fibers which have bend in the z-direction. The load during testing
was exerted in the vertical direction on the sample. From the figure, it
can be regarded that most of the fibers are still intact but have changed
location. This means they could move freely through the matrix during
deformation, which would be another indication that the matrix is dominant
during compression of the sample, resulting in a viscoelastic
nature of the composite, based on the polymer properties.
Based on the observations done it can be stated that under a compressive
load, the GPP polymer tends to exhibit a viscoelastic behavior. In
practice this means that there is a positive relation between the applied
strain rate and the yield stress, and a negative relation between the
temperature and the yield stress. The addition of fibers, in this case
glass fibers, does increase the compressive properties of the composite,
however, the polymer properties remain dominant in the failure mode. n
DE APPEL 39