Shape Memory Facade

Contents

Foreword, Individual design 03 Farid Boussihmad 04Dimitrios Sampatakos 10Erfan Zoakman 14Group Design 18Principles 18No energy consumption, separate adjustability of each unit and self adaptive? 19Shape memory alloys - Nitinol 20Memory alloy in the sun shading system 21Constant shape change and use of shape memory effect in the project. 21Implementation and design 22Rhombus and nitinol 22Description 22Motion and driving force 23Experiments and Reaction Force 24Final design 26Use of the sunshading system on a real building 26Adaptive to the outer or inner climate? 27Conclusion 28Evaluation 28Bibliography 29Additional Renders_Photos_drawings 30

03

Foreword

During the Bucky Lab course each one of us tried, first individually and then as a team, to de-velop a truly efficient and innovative sunshading system/mechanism. The final design of the shape memory facade tried to fulfill as many initially set goals as pos-sible. The development went through different phases of research, experiments and model constructions in order to observe different aspects of what would later become the final design of a sunshading system or facade layer. The focus point and challenge in this procedure has been the word “innovative”, the smart function and effectiveness of the structure. Due to the nature of the materials and elements used it would have been impossible to accomplish the final group design without testing from the first moment of the idea until the last moment of the construction of the model, which finally gave us the satisfaction of having created something we developed ourselves going through all the difficulties of such a procedure. From the begin-ning until the last part support from our tutor Dr.-Eng M.Billow has been a determinant factor for completing the final design.

Individual design

The first part of the course included individual designs and development of Sunshading sys-tems.

Farid Boussihmad: Snow globe facade

Dimitrios Sampatakos: Braided structure-Medical stent

Erfan Zoakman: Pupil Sunshading

04

Farid Boussihmad

Snow globe facade

05

At the start of the Bucky-lab course, my enthusiasm was really big. Coming up with an own sun shading idea, that didn’t exist, and research this idea and eventually realise it in a realistic prototype is a chance that I didn’t get before this course. The introduction week and various excursions, made this feeling only grow more and more, till...

CONCEPT

Till the moment, when we got the chance to actually sit and come up with an innovative sun shad-ing idea. How does one come up with an idea that didn’t exist. I think this is a question that is worth a book to write about. So after some effort and thinking, the enormous enthusiasm descended and made room for some concern.

The advantage of working in groups in one atelier, is that one can make a tour and see what the group mates are up to. Are they facing the same difficulties, or do they actually have the ability to come up with an idea that didn’t exist yet. After some conversations with some group members, I discovered that most of the people didn’t come up with an idea in some seconds. It is however a search in a certain direction for an possible idea.

So my first direction, that interested me most, was the idea of an adaptive sun shading system. An system that is smart enough, to know when to shade and when not. The journey for a new idea began, when I opened Google and typed: Adaptive sun shading.The moment that the journey star-ted, was the start of getting different ideas and concepts. Most ideas fall apart when thought about more, and some survive the thinking, but fail when sketched. The disadvantage about searching for a new idea, is the fact that many different ideas come to mind. It can be compared with standing in the dark and grapping around, to catch different things every time. At this stage I realised to add some parameters to my search and start searching in a specific direction. This direction I made clear by sketching some sun scenario’s.

Figure 5.1: sun shading during different scenarios: cloudy, semi cloudy and sunny.

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DEVELOPMENT

I found many existing ideas and some I found very interesting. Some examples:

Researching more on this topic, I came to know that there are different ways to design such an adaptive sun shading system. I found some interesting examples for this system. However most examples were just concept ideas, and not a concrete working solutions. This stimulated me to re-search further in this direction.

While drawing this scenario’s, I came up with a concept for sun shading: A material that darkens by exposing it to the sun. After some research about this, I came with the existing properties, which is named by Photo chromic materials. These materials change under the influence of light, later I came to know, due to Mr. Marcel Billow, that there are also Thermo chromic materials (change un-der influence of heat) and Electro chromic materials (change under influence of electricity). I was really enthusiastic about this new material properties. Because the system will be designed to block sun light, it was for me naturally to go for a photo chromic material. I soon discovered that this ma-terial is being used on various fields. For example in some glasses, this material is used to function as a sunglass when the sun is shining.

After more research about this material and consultation with the teacher, I came to the conclusion that it is not an innovative idea to use an existing material, but change only the application and the size. I had to think in another scale: same principle but with different scale. This made me look back to the previous systems of the adaptive sun shading examples.

It is funny how sometimes this process of designing works. After many effort and research about the principle of photo chromic glass, it was swiped out by a single shower that I took.

It was in a morning before the consultation with the teacher, that I decided to take a shower. And that shower changed my idea completely. I was showering and looking at the water drops fall down. I was fascinated by the effect of blocking the view, but still giving some view though the water. It felt like I saw it the first time of my life. My thoughts wandered away to the Bucky Lab assignment, and I started to think about it, and tried to apply this shower phenomena to the sun shading solution. What fascinated me the most, was the fact of combat the heat of the sun with water drops. And in that direction snow came into my mind, snow is colder then water. So It would be a great solution to combat the heat of the sunshine with the cold character of snow. There the idea of a snow globe facade was born: There has to be a kind of mechanism that make it snow when the sun shines. A Snow globe is a descent comparison.

Figure 6.1: example of an adaptive sun shading system: the different layers make sure the light is blocked completely, partly or passed through.

Sunshading systems

Concept Idea: Colour changing Glass

Photochromic materials change reversibly colour with changes in light intensity.

Thermochromic glasshttp://www.aisglass.com/swfs_solar_heat/pdf/Thermocromic_Glazing.pdf

Sunshading systems




Figure 6.2: another example of adaptive sun shading.

Figure 6.3 : photo chromic glass: The glasses at sunlight.

Sunshading systems




Figure 6.4: Snowflakes blocking the sun.

07

After some deeper thoughts and consultation with the teacher, the next step is getting the brains thinking and the hands dirty. I had to experiment with different objects and make sure that the idea actually works. First thing I explored, was how the snow globes were made. There I came to know that it is actually quite simple. One needs 4 basic things: a waterproof pot, water, some artificial snow (which can also be made from chalk) and last some Glycerine. The ingredients are quite logical, except for the glycerine. Glycerine is used to make the water heavier, so the snow floats slower and constantly.

After some searching I got all the materials needed, so the experiment could start.

The experiment went well, and I came to know more about the system and how to proceed. The most important conclusion, is that water alone is not enough to translate the snow globe idea into a working solution. Simply because the snow does not float that much, it had to be turned upside down several times in a short period to maintain the snowing effect. The other challenge I faced, was the question how to keep the facade snowing, when there is constant light. Naturally it’s not possible to turn the building upside down, like it’s done at snow globes. But there has to be a solution for that.

The pictures above displays the progress of the snowing. It shows the view that is blocked if it’s fully snowing, and how the view gets better when the snow is floating down. To make the floating slower and better, glycerine was the solution for this. However, the amount of glycerine has to be limited, because otherwise the water will have a bigger density than the floating elements, which will result in the elements not floating but stay on top of the water.

Sunshading systems

Concept Idea: Sneeuwboll effect

Figure 7.1: snow globe.

Figure 7.2: starting ingredients for the experiment: waterproof pot, water, glitters and glycerine.

Figure 7.3: The stages of the snowing facade.

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The other problem I faced, was the question how to make the facade snow when there was sun-shine. The first idea’s was to make the system work manually, simply by creating a pressure box on the bottom of the facade, which can be pushed against. This push will create an pressure that blows the snow into the facade.

I was not satisfied with this solution, so parallel to developing this system I was thinking of better smarter solutions. Soon after some thinking and turning back to the beginning concepts of adapt-ive sun shading, I came up with some idea. The idea that the sun shading is needed when there is sunshine, and when there is no sunshine, the shading is not needed. So there has to be a system that is activated by the sun.

The famous system that works on sun, is off course PV-cells. These cells produce power under in-fluence of UV-radiation. Now we found ourselves a power source, we need a system that works on this source and makes sure that the snow will float on the facade.

This solution is found in a water-resistant propeller. This propeller should be driven by PV-cells and it should rotate harder when there is more sunshine. Resulting in the facade to be snowy, which will block the sun radiation. At this stage the major solutions for this system were found, there were some minor application problems that had to be solved. Like the resistance of the system against water, the resistant against freeze and the integration in a real facade. Because of the mid-term present-ations arriving, these problems should be tackled after the presentations, if the idea is chosen. The concept idea works, quite well, as shown at the presentation. However, there are some question marks, which had to be solved.

The next step was actually finding a PV-cell and propeller system, and test that, so I can be more certain that the system actually works. I searched for the tools, and I found one system which comes with Lego. It was a set of Lego to build a helicopter, there was also a propellers driven by PV-cells. Unfortunately the engine of the propeller was not water resistant, so I could not combine the system with the floating snow, and test the whole system. However I could assume that it will work perfectly, just by testing the different systems apart from each other.

Figure 8.1: manual system to push the snow into the facade.

How to keep the system circulating.

Manually

Automatically

Solar radiation ->

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Waterresistant fan


Manually

Automatically

Solar radiation ->

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Waterresistant fan


Manually

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Solar radiation ->

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Solar radiation ->

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Figure 8.2: snow globe facade that is driven by PV-cells and propellers.

Figure 8.4: propeller spinning under influence of radiation.

Figure 8.6: the three situations, and the reaction of the facade.

Figure 8.3: water-resistant propeller.

Figure 8.5: Lego system with propellers driven by PV-Cells.

09

CONCLUSION

Looking at the design at the end of the mid-term period, I think I can assume that the design has been developed very deeply, it is a simple to the point system. Elaborating this design, there are few things to solve, such as the integration with a building facade and the resistance against cold and freeze. However, I assume that the solutions for these problems lay within fingertips. However, build-ing a prototype, I’m sure will give some minor problems, that were not elaborated yet.

I, however am content that my design is not chosen to be elaborated more. Because the challenges that lay in this design are not that big, there are only some little points to be solved. The nitinol design, however, gave us more resistance, and made us make some serious thinking and come p with solutions.

Figure 9.1: render with a working snow globe facade.

Figure 9.2: Experiment with snow floating in a pot.

Figure 9.3: Experiment with snow floating in a pot.

10

Dimitrios Sampatakos

The development of an innovative shading system/mechanism within the bucky-lab course has in my case gone through many different phases comprising seemingly disparate solutions. On a closer look and analysis however they have all been part of an attempt to combine aspects connected to energy efficiency, to the possibility of self adapting to the environment (needs to shade more or less in different parts of a facade or even within a window), separate adjustabil-ity of each element of a whole shading system and in some cases to visual aspects and the way the human eye perceives images.

Design aspects and beauty of the final product has not been a starting point or an inspiration for me to create a specific solution although I strongly believe that a really interesting and clever system that actually works and fulfills many requirements can much easier be designed in an eye-pleasing way than the other way around. (apart from the fact that in my opinion innov-ative engineering has a beauty in itself). Most time of the semester has thus been devoted to research, experimenting and development of different aspects of the final design, instead of working on the details of one idea (almost) from the beginning to the end. One of the first phases of my research started with setting the basic demands of such a system/mechanism and thinking of properties or features current systems don’t have, or what I usually don’t like about them. The solutions I dealt with during this seeking/search of a truly innovative shading device were usually based on one or more of those requirements, usually fulfilling one of them to a large extend and in a later phase combining some others too. Goals/requirements for the Shading System:

Energy Efficiency “how is it driven”

Adaptability to the environment

Adjustability of each element

“Smoothness” of shadow/ outside view

The first steps and ideas were mainly about the visual aspects and a possible combination with an efficient mechanism. Many shading systems had as I found out problems with a percentage of the façade surfaces being completely intransparent and the rest part completely transparent (100%-0% transparency). The bigger the elements for shading (intransparent part) the more they prohibited the view to the outside, especially in certain angles or from certain perspectives close to façade/window surface. Smaller shading elements create a better, smoother view to the outside even at different viewing angles or distances. An example for that are half-transpar-ent fabrics widely used on facades. The Fibers of the fabrics are in that case the 100% intrans-parent elements, which because of their very small size create a smoother shaded picture of the external space. Even in that case however a view from a close distance was more prohibited than one from a longer distance. Thoughts about eliminating the problem led to two directions that I tried to combine in this stage of my research. First I wanted to make use of the principle that a division of a façade or window in smaller parts of transparent and intransparent elements will create a smoother shaded picture of the outside world. Thus fibers, thread and strings were used in some experimental models. Different overlapping shapes and use of more than one layers made it possible to create different degrees of transparency by moving the ends/fixing

points of the fibers or by rotating them to wrap the fibers around each other.

Figure 10.1: Models used for studying overlapping and different density/transparency points within fiber structures, smoothness of shading

Figure 10.2: Different visual perceptions due to angle/dis-tance. Possibility of making use of density points during eye movement.

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Even in that case the smoothness of the view in very close distances to the fibers was not perfect. (Overlapping of layers also creates different degrees of transparency from different angles if they are not placed within a few millimeters of distance). A characteristic picture that can describe the whole problem is when someone has a very good view to the outside when looking at a window covered with venetian blinds, but needs to push them apart with his hand when he comes very close or needs to see at a specific angle. The next step was setting a challenging question connected to these problems: ”Is it possible to make certain surface of X% transparency so smooth to the human eye that one cannot distinguish the 100% intrans-parent elements from the 100% transparent part at any distance?” The first thought was mov-ing pictures and frequency. Research led to already existing projects using rotation of circular surfaces that comprised a transparent and a printed part. However the use of Fibers, linear elements and research into energy efficiency matters made vibration/oscillation the object of investigation in this case. This happened while simultaneously searching into the possib-ilities of making use of wind energy through rotation or oscillation/fluttering of elements as constantly moving parts are highly energy-consuming. The “windbelt” was one of the recent innovative ideas in this area, using a thin plastic stripe (similar to a belt) that oscillates/flatters when wind flows through it. Combining more of those stripes to create a shading system was an idea that was abandoned due to reduced airflow on a building façade, possible noise prob-lems and because at that phase vibration would be a way to visually smoothen the shaded view.The findings showed that it is indeed possible to create a completely smooth picture of the outside by using vibration of a linear element. Frequency will only have an effect on the per-ception of the movement from the human eye not on the shading percentage. This means that a surface 50% covered by an instransparent part will have 50% of its area completely (100%) filled and 50% of its area completely (100%) transparent. However different viewing distances/angles, as mentioned before, may change the visible part. When in motion the whole (100%) area will in this case have a 50% transparency and a perfectly smooth view from any distance if the frequency is high enough (for example more than 40%) and only if the filled parts are evenly spread within the surface and have the same motion/period of motion.

Use of vibration and generally motion in the sun shading solution of the course was aban-doned due to the difficulty to use it as a truly energy efficient device. No use of mechanically/electrically driven parts OR hand operated systems will at the end of the project research pro-cedure be the ultimate goal. At some point the innovative windbelt, an oscillating plastic stripe that makes use of wind energy was a subject I observed to use as a sunshading element, but dependence on wind and not smooth and sufficient flow close to a building facade created problems.The next step in the development of the final shading system was researching more into pos-sibilities of changing the percentage of transparency without using more layers (only work when layers are very close to each other). Linear elements had to change in number or width within the surface to allow adjustability. This thought led to the well known poisson’s ratio, to tensile/compressive forces exerted longitudinally at the ends of the linear elements and also to experiments with elastic bands..

Models were at this stage similar to the ones created with fibers/thread because of the linear shape of the shading parts, but adjustability was in this case achieved by tensile forces. Pois-son’s ratio, being the relation between linear and transverse strain (change in length/width), means in this case that an elastic band becomes thinner -to a certain amount depending on its properties and force- when stretched. One simple solution making use of this principle was for example a number of parallel elastic bands attached/fixed on one side to a frame and on the other side to a rotating rod. Rotation of the rod exerts tensile force on the bands which be-come thinner according to poisson’s ratio, thus covering a smaller percentage of the façade or opening/window.

Figure 11.1: Outside view prohibited more or less accord-ing to intrasparent part shape/width. Same percentage of transparency, less prohibited viw from more angles. Reason for searching into of fibers/linear elements.

Figure 11.2: Overlapping of fibers, different arrangements. Exploring vibration and transparency with shutter speed and focus. (effect of frequency?)

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Experiments with elastic fabrics showed that using many stripes of them would mean that very high tensile forces as well as many cm/m of elongation are needed to stretch them enough. According to the theory pure rubber has a poisson’s ratio of almost 0.48-0.5 (poisson’s ratio: v= transverse strain/longitudinal strain. Strain is ΔL/L) . This means that for an elongation of a 5cm wide and 1m long stripe of 100% rubber to 2m length the width will become 2.5 cm. Relatively high forces are usually required to stretch the band to more than double its size (impossible to be hand driven if many bands are being used especially without some special linkage to reduce the force needed.) , rubber is rarely used as a pure material and will also be problematic after a certain number of deformation cycles. It will certainly become dry and loose part of its elasticity even without being exposed to the external environment. Mainten-ance and accurate operation of the system will be a problem due to the properties of rubber. As in previous cases energy consumption would in this solution also be high because of high tensile stresses. The drawbacks of rubber stripes changed the direction of the research to other materials and elementary shapes that could be part of a linear element within a façade. Investigating the properties of rubber, the definition of elasticity/poisson’s ratio and the cause for these properties one confronts with micro scale atomic bonds and arrangement of atoms. These bonds can be visualized/illustrated as a stretching honeycomb or grid. Longitudinal tensile or compressive forces cause the rearrangement of these bonds that become longer (stretch) in the direction of the tensile force, but also thinner in height/width in order to pre-serve their bonds and basic structure.

This effect can be easily shown in a linear structure as a grid of interlocked/connected crys-tals or rhombuses and has also been the inspiration for the next stage of the development.As already described problems caused by the properties of rubber needed to be avoided (dry-ing, high energy consumption, high non constant forces), but at the same time the effect of reducing the width of a linear element under longitudinal force should be preserved. Much lower force to operate the mechanism would be preferable as well as a good ratio between transverse-longitudinal elongation under force.

These requirements caused the research to focus on braided structures based on the basic shape of a transforming rhombus. This arrangement would keep the effect of width change under length change without using elasticity, but thin and strong fibers.

One of the most characteristic structures of this kind are medical stents. They have been an important point in the whole procedure of seeking the most effective system as their structure and material were a strong influence for the final idea/solution. Medical stents are braided tubes inserted into the human body in order to prevent or cure localized blood/air flow con-striction. During a surgery they are inserted as very thin tubes (very small diameter) into the artery/vein/esophagus etc and after placement in the specific area their diameter increases significantly exerting a constant reaction force on the artery walls to keep it open and improve flow. The change in width/diameter of medical stents was at first achieved by inflation of an internally placed balloon that pushed the stent open when placed into the human body and was removed right after. The material of the stent (metal) had properties that made sure it would stay in place and its diameter would not be reduced. Development of material science and technology very soon caused improvement in the design of medical stents, but especially in the materials used. So called “smart materials” were a very important recent development that medical science made use of. Stents are now made of smart alloys and polymers that can self expand within the human body. Expansion is usually actuated by temperature change, using the temperature difference between the environment (or specific place where they are kept) and the human body. The properties of these smart materials and possibility of energy efficient design (no electricity, no human force required) were the basic principle used at the final stage of the development of the innovative sunshading system and an important focus point of the whole project.

Figure 12.4: Possible ways of streching (rotation etc) linear elements/fibers or different overlapping arrangements. Thermally actuated compression that leads to denser arrangement

Figure 12.3: Fibers extending bey-ond transparent part for transpar-ency and being compressed into transparent part (glass/window) due to heat for shading

Figure 12.1: Braided protection sleeve found in computer shop simulating effect according to medical stent inspiration.

Figure 12.2: Model for inflating (bicycle pump) balloon inside a braided tube. Idea from proccess used during surgeries (stents) and artificial muscles.

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At this previous stage research was focused on the actual design and structure of the stents. A very similar braided fiber tube was used for experiments. It is usually used as a protective braided sleeve for electric cables or water lines. ( in some cases also fire protection) This braided sleeve showed some very strong advantages over stretchable rubber elements. Much less longitudinal tensile or compressive force was needed to change the tubes width. Experiments showed that when fully compressed (4cm length) the width of 17mm changed to 7mm of width when fully extended (10cm length). This change ratio is a result of the ba-sic rhombus shape as a multiplied unit within braided structures or grids. The change of the rhombus shape from a perfect rectangle to a slender shape that tends to become a line in the horizontal or vertical direction respectively under diagonal force (pushing the corners closer to each other) gave more development possibilities to this design, whether it would be used as a surface or a tube. Research this time led to existing innovations like the worm robot, or artificial muscles, which use a very similar braided flexible tube that can change its width anywhere along its axis. Change of width anywhere along a tube was at this stage a very important aspect and ad-vantage over elastic bands as one of the main requirements has always been adjustability.

Braided flexible “stent-like” tubes were at this stage designed at different scales to observe how they could be implemented in a façade. Designs ranged in scale, starting from a big tube wrapped around a transparent glass building. The tube could at any point of its length be-come thicker and denser to create more shadow as a reaction to sunlight, looking similar to a moving worm along a facade. In a window or “one office” scale the same design looked like parallel linear tube elements which were pushed or stretched at different points along their axis to become thicker or thinner according to the shading needs.

This development phase ended with observing the possibility of using the principle of the braided structure or grid that can become denser at different points due to the change of the rhombus shape. Thinking of future designs and solutions a smart grid or braided surface that will be adaptive and change/adjust its density (of the grid) at different points according to the light would certainly fulfill the requirements of adjustability and adaptability. In sketches that showed the idea a surface of this kind could have connected corners at all rhombuses (of small size) and at any point of the surface the connection could pull the corners close to each other to create a denser area. This could happen automatically with light sensors but at a later stage also add a high-tech mechanism of tracking the eyes, faces of people in a room or the computer/tv screens in relation to the sun position. In that way very specific points of the grid will be able to become dense and protect eyes and screens from direct sun in offices for example without sacrificing the other advantages of sunlight. This part of the development of the innovative façade system has been mainly connected to the basic structure and how it could fulfill the requirements of adjustability of each element separately and adaptability, even if it is until this point mainly mechanically driven by electri-city.The next phase is a more focused research on energy efficiency and how one of those “dia-mond/rhombus shape” based structures could self adapt to the environment without any en-ergy consumption at all. Until this stage most of the research concentrated on small scale elements as smoothness of shadow and outside view were a starting point. This meant that mostly fiber-like linear units were arranged in different shapes, geometries and overlapping positions in order to adjust transparency. Photography with different shutter speed tried to show the effect flattering or oscillation would have with those fibers. (thread,string,plastic etc)However as a real shading system of a façade these fiber based solutions were difficult to realize and implement in order to become a reliable and effective mechanism, especially with the limited means of a student project. Thus the first parts to a large extend had an experi-mental and theoretical direction.

Braided crystalline geometry (observation):

Fully compressed width: D0=17mm Unrestrained width: D=8mmFully extended width: De=7mm

Fully compressed lenght: L0=4mmUnrestrained length: L=9mmFully extended length: Le=10mmFully extended length: Le=10mm

angle b between rhombus side and vertical axis (depending on braiding pattern):

Fully compressed angle: β0=20*Unrestrained angle: β=25*Fully extended angle: βe=70*

Bucky Lab_Shading System_Dimitris Sampatakos

Figure 13.1: Idea of tracking sun and ojects of the inside space that need shading

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Erfan Zoakman - Pupil sun shading systemConcept

The assignment for developing an innovative sun shading system for the bucky lab was not an easy task like I assumed before starting with the project. This project was in many ways differ-ent then the projects I have done before in the bachelor. In the bachelor where we were busy with designing a hole building was now turned in to designing just an element of the building, the sun shading system.

An other difference was in my opinion that this project didn’t have a location or an environment where you had to reckon with. This system has to be integrated in every kind of building and fa-cade. Beside this, the design had some other requirements, like the sun shading system should be automatic and durable. The system should also have the solution shading the sun but also give the users of the building the chance to look out even with the sun shading infront of the window.

Design a sun shading system which is innovative is not so simple. Because most of the time you associate the new design with the existing ones. Through the process you realize that it is not possible to design something which is never made before. You compromise your design with the existing techniques and find fascination in other things then the building productions to develop the right design. Which in my case was the human eye.

I started with the first fascination of a pin-art wall (see figure). The idea was adding a surface with many of these pin-arts to an existing facade and make them move in and out to shade when needed.This idea was changed instead of pin-arts using umbrellas. These umbrella’s would open for sun shading. There were different kind of umbrella’s which could be used. So I searched for a type where it can have more functions then only sun shading. The solaris umbrella was an um-brella type which had on the outside surface solar cell layer which can generate electricity and shade at the same time.After taking a critical look to this idea it was clear that it had to many components which didn’t match with each other and formed more an idea which was not really innovative. Even by re-searching very good I found a design for a building where they have used this idea also as a sun shading system.

The next thought that come to me was not designing a sun shading system but creating a sys-tem which can redirect the diffuse light from outside to the inner space. Because one of the main problems with sun shading system is, that if you want to block the sun completely you have to use something which is not transparent nor translucent. But you want also at the same time to have view to outside without being blinded by the sun.So by starting from a normal sun shading system which can cover the hole window, I researched for systems which can redirect light. I found as a solution fibreglass which can redirect light. These fiberglass could be putted in a system on the outside facade and connected to an inner space which can be lighted up by the diffuse light which is brought by the fibreglass. In my research for this solution I came across a manufacturer which produces panels with unique luminaries made from fibreglass which can be located on the roofs or façades of buildings and flow the sunlight in to areas in the building which don’t have any windows.This made my enthusiasm for the idea gone, because it showed that the idea was also formed in a developed product.

Figure 14.1: Eye pupil

Figure 14.2: Pin-art bookshelf

Figure 14.3: Umbrellas

Figure 14.4: Solaris umbrella

Figure 14.5: Parans panel

Figure 14.6: Working of paran panels

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There for I started searching for another fascination. From this point I left the mechanical and technical products and started searching outside the manufacturing world. Here it was that I found my idea for the sun shading system in the human body. I was fascinated by the human eye. The pupil of the eye which reacts on the amount of the light which falls on the eye and shrinks and grows by that.

For me it was the task to integrate this function of the pupil in a product which can be manu-factured and used as an sun shading system. By making a research on how the eye works and how the pupil can shrink and grow. I found different kind of options to make it in a product form. The pupil of the eye is connected to two types of muscles, circular and radial muscles. When the pupil becomes small the circular muscles become contracted and the radial muscles extended. When the pupil grows the muscles react opposite. From this I made some sketches about how it can work as an mechanical system.

I have thought of different systems and techniques to imitate the growing and shrinking of the pupil. The first one was using a sheet which can expand by the heat of the sun and shrink when it is cooled down. For this I have searched the different kind of chemical conditions of different kind of materials, to find a material which can change very easily by a small different of temper-ature. The conclusion at the end of my search was that, gas expands more than liquid and liquid more than solid type materials.

The first design began by using a bag form with gas in it, which can expand at higher temper-ature and shrink at lower temperature. The problem that I encountered with this design was finding a material for the bag that can very elastic. Because the expanding of the bag should something in the range of 10 times bigger as the shrinked size. So finding the right material for this design was not possible, even if I would find it, it would be a very expansive material which would cause problems in later stage of the project where I would have to develop and build the design.

The second design that I have approached was more inspired on the functions of the pupil mus-cles. I thought of an hydraulic system which can represent the radial muscles. These hydraulic tubes which can extend and contract pulls on a ring which is connected to a fabric, which will extend when the hydraulic tubes starts to contract. Here I had to deal with two problems. The first problem was the fabric. This fabric had to be very elastic so it can cover a window of 1m by 1m and at the same time shrink to 10cm without to much buckles in the fabric and avoiding that the fabric will hang loose over the window. The second problem was also related to finding the right material. In this case for the ring. The ring would be pulled by the hydraulic tubes so it can stretch the fabric. For this the ring had grow in diameter, that’s why I had to be also from a very stretchable material. Which was also very hard to find.

After thinking over and over again about this kind of design a lot of them could not be devel-oped because there were every time some problems which couldn’t be solved. At that point I realised how much an architectural students lacks knowledge in mechanical and technical productions. I was very glade that I could realised this trough this course. That’s why I started searching outside the architectural faculty to gain more knowledge by going to other faculty’s which had to do more with mechanical and technical stuff. My first step also towards the 3Me faculty. By talking with a friend at the mechanical faculty about this project, he introduced me to one of his professors which was specialised in micro-techniques. This subject was dealing with al kind of manufacturings. After making an appointment with him and sitting talking about the project and about my fascination. He gave me some great examples about how it could be developed and some systems which were manufactured at micro level but still had the same system type as I wanted, also the things that I should reckon with.

Figure 15.1: Muscles working pupil

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I was surprised how quick mechanical engineers could think from just an idea to a whole man-ufactured product. After gaining the knowledge from that conversation, I started again with designing. This was the part that found the solution to my fascination in a design form.

The design that I have then made was a to sheet form filled with liquid. The translucent col-our would make sure that no sun light will enter the space. And when there is no need for sun shading, the liquid would be vacuum and the two sheets will starting come to each other in the centre and start compressing the liquid to the sides of the sheet. This will create a transparent opening in the middle of the sheet and start growing as more liquid is vacuum. The effect what you get with is, is almost exactly the effect of an eye pupil.

Development

Of course this design wasn’t also without any struggling. The problems which I encountered where not anymore in the field of materialisation and not finding the right material for it, but more in the technical part.

For this I made some goals which I want implemented in the end product. First of all, the prod-uct needs electric energy for the vacuum machine. So my goals for the energy was that the sun shading system should win his own energy and use that for the vacuum machine.Beside this each panel should be adjustable separately, in case one panel used for one window. Or if many smaller panels are used for one window, then it could be controlled as one panel. I should reckon with the weight of the panel, by adding liquid the weight of the panel can very heavy. Also the vacuum liquid should be kept some where temporary, so it can be pumped back in when needed.

Also some question which a rise are like, should the system be putted in front of a facade, or in between glass, or inside the building. Also how it can been replaced when the sheet is broken or damaged etc. Not for all of these questions were answers found. It wasn’t also very problematic, because the first phase of the bucky lab project was more focused on developing an idea for the sun shade system and think about the major aspects of the sun shade, like how it works, what kind of materials you need etc. In a later stage the design would be developed to an real product and designed all the details of the product.

So because the system was really sensitive in the mean that it can’t really held up hard weather conditions and forces, I have decided to put the system between the glass plates. And create space above the sun shade system where the reservoir for the liquid could be placed and also on the outside of the solar cells for gaining sun energy. For the electricity of the vacuum ma-chine. The vacuum machine would be connected to the sheet with tubes where the liquid can go trough.

Figure 16.1: Sections sun shading system

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Conclusion

Concluding at the end of the first stage of the bucky lab project, I can say that it took a lot of time to come up with the right idea that can be developed and build. That’s why the end product has many question marks. It’s an high tech solution as an sun shading system, but it needs a lot of time and energy to be developed to an working product. By making models I figured out that even building a small model of the system can have so much problems.

So the idea needs to be simplified and approached more from the view point manufacturing to be able to develop it further. So the problems like water tight, weight and integration in the building could be solved for the end product.

Figure 17.1: Gaining electricity with sun shading system

Figure 17.2: Frontview sun shading system

Figure 17.3: 3D model sun shading system

Figure 17.4: Layers sun shading system

Figure 17.5: Sun shading system in a real building

Figure 17.6: Scale model sun shading system

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Group Stage.

Principles

Beginning the development of the facade system as a team some basic requirements had to be set in order to proceed and make important choices. Possibly innovative ideas had to be sacrificed in favor of a working model and an integrated design that fulfills to the most possible extend the most substantial goals and challenges. In this hierarchy energy efficiency that at a later stage evolved to the strict rule of zero energy consumption ranked first. Other very im-portant goals were adaptability to changing environmental conditions or shading needs and adjustability of each unit of the system separately (which means that units should not be con-nected to one central sensor or mechanism that adjusts them all at once).A combination of these requirements led to the final design and models.

At a first stage the design had reached a point where a braided (grid) structure would fulfill the requirements of adjustability of every unit within the façade. Inspired by the structure of the medical stents used to improve flow of blood or air in the human body and the way a braided protection sleeve for computer wiring represents its changes in width along its axis, research focused on solutions for making the tube or surface more dense or wider in specific parts, ac-cording to the weather conditions and sun.

Using the rhombus geometry as the basic unit of a braided surface (that could be in one plane or form a tube) the design would make use of the form change of the rhombus due to forces along its diagonals. Compressive force pushing two opposite facing corners close to each other have an effect on the other axis, pushing the other two corners apart (see figure). This is the reason why any longitudinal compressive force between two points in a braided tube will make the tube wider between these two points. In a surface it will create a more dense spot between the points (see figure).

As proved after research in previous stages those grids comprising fibers or wires can fulfill the requirement for adjustability without the need of excessive forces (as seen in other designs with elastic bands that are stretched to become thinner according to the poisson’s ratio). Surfaces of varying density points can be created by connecting the corners of the rhombuses and exert-ing force between them. As a parametric design project/idea each bond (or connecting corner) could be programmed to move towards (or away from) the opposite corner to create more or less dense spots according to the needs. Simultaneous tracking of the sun and of internal space elements (even people’s eyes, computer screens etc in offices) could instantly create moving dense spots within the grid to protect only selected parts from the sun rays, but at the same time make use of the sun heat and light.

Figure 18.1: braided grid changing transparency at different spots

Figure 18.2: rhombus deformation by corner forces

Figure 18.3: medical stents Figure 18.4: testing with braided cable sleeve













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The same adjustability could be integrated in a tube shaped braided system (keeping the stent design) similar to the innovative robot worm or artificial muscles. In that case width and density of the tube would change according to the needs making use of the same principle of the com-pression of rhombus corners between specific points. A choice had to be made at this point to proceed with only one of the braided (grid) design solutions. The answer was given by the hierarchy of the goals for the final design. Complex solutions that would sacrifice energy efficiency and effectiveness of the model for more utopian innovations had to be simplified. Keeping the surface (one plane) rhombus grid design, the next step was to focus on improving efficiency and deciding on the way it would finally oper-ate. Adjustability has been already guaranteed by the design of the grid elements, but the final façade system should be able to adjust each of its units separately according to the needs of that specific point. This would be energy and material consuming (and very expensive) if each unit needed a separate sensor.

No energy consumption, separate adjustability of each unit and self adaptive?

The inspiration of the medical stent (see figure) at a first stage has been much more than just an idea of a braided wire structure that changes its shape under longitudinal forces at the corners of the elementary rhombuses. It was also more than an effective alternative to elastic elements of changing width (under tensile forces). It was also an important influence in terms of opera-tion of the whole system. Development of smart materials recently used for making these stents was a turning point for the project. Operation of any chosen design would in almost any other case need sensors, a large amount of connections, electric motors, a central processing unit to control all sensors and “give instructions” and many other parts and devices that would be dir-ectly proportional to the complexity of the design, the number of shading units and the need for independent motion of each part. An adaptive system as inspired by true parametric designs would in that case mean hundreds of smart programmable bonds/corners that operate under an ultra complex system with a central control unit. This would in such a design not be energy efficient in many ways and is of course at this time still an architectural utopia of a “living skin”.

The development of the sun shading mechanism concentrated on the use of smart materials that would fulfill all three requirements:

First, NO (Zero) energy consumption to operate the whole system (see figure). This means no electric motors, no connection to electricity for operation, no sensors and not hand operated. The shading system can be assembled in the factory and just be attached to the façade and will then be ready to work even if the building has a power blackout and no central generator.

Second. Separate adjustability of each unit according to the shading needs (see figure). Not just a central adjuster/motor that moves many elements at once. This practically means that the number and size of units only depends on the amount of available material (and price) and the needs of the building. Every single unit will react on different conditions.

Third. Self adaptability. No sensors needed, no device will need to give information to the sys-tem about specific shading needs (see figure).

Figure 19.1: experimenting with braided aluminium grid surface extended

Figure 19.2: Adaptive surface with different degrees of transparency. (density change)

Figure 19.3: “conventional” adaptive surface. Motor, sensors etc. to have each element adjustable.

Figure 19.4: adjustable too different conditions

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Shape memory Alloy- Nitinol

Smart materials used in medical stents are shape memory alloys or polymers. The braided tube self expands due to the change of temperature between the previous environment and the body temperature. Shape change is actuated at a specific temperature. It will come back to the “memorized shape” of a wider tube only when the material reaches this temperature (which in that case is adjusted to be the body temperature).

Nitinol theoretical part:

The word Nitinol refers to the two materials comprising in nearly equiatomic quantities the final alloy, Nickel and Titanium, and to the laboratory where the alloys were first research namely the Naval Ordnance Laboratory.(n.o.l)As already described this shape memory alloy will even after severe deformation return to its previous shape when heated above a specific transformation temperature. Pseudo or Hyper- Elasticity, one more characteristic of this alloy, is the elastic response to an applied force that allows the alloy to return to its shape even at very high strains after removal of the force (high elongation in this case). This can in some cases happen even without applying additional heat if deformation and force removal happen just above the transformation temperature.

The properties of Nitinol derive from an internal phase change of the crystal structure of the material called martensitic transformation. When Nitinol is warm (well above transformation temperature) it is stable in the austenitic phase (arrangement or structure) and has properties similar to many titanium alloys. When Nitinol is sufficiently cooled to temperatures lower than the transformation temperature it adopts another crystal structure called “twinned martensite” and its properties change dramatically resembling those of lead or tin, very “soft” metals. Re-covering from the cold martensite state upon heating to the austenite arrangement brings the material to its original shape and crystal structure (see figure).

High forces are produced when return of a deformed martensite to the previous austenite struc-ture (and thus shape) is prohibited. This happens because nitinol is an intermetallic compound, which means that in its stable crystalline phase atoms have very specific locations within the lattice (see figure). Transition temperature of this shape memory alloy can be changed (adjusted) by slightly chan-ging the composition of nickel and titanium which normally is almost equal . To preserve its hyperelasticity and shape memory properties transition temperature can be adjusted/defined from -20 to +60 degrees celcius.

Figure 20.1: martensitic and austentic phases of a memory alloy in changing conditions

Figure 20.2: atomic arrangement change in different stages

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Memory alloy in the sun shading system

Smart materials offer many new opportunities for more efficient, self adjustable and adaptive systems in architecture. We can observe that shape change according to temperature which can also be precisely adjusted is a determinant factor for achieving the energy efficiency (no energy consumption) and adaptability set as a requirement for the project.

In this specific application of a sun shading device or mechanism the transition from one shape/structure to the other due to temperature change can be used either just as the driving force for the system, or as a shading unit in itself. The second case would mean that the shape memory alloy would be used probably as a sheet or other surface of a certain size, that would due to temperature change its shape to shade more or less depending on the needs (see figure). A simple and reasonable design of this kind would include a sheet of shape memory alloy as one –multiplied- unit, which would have a folded shape of smaller sun-facing area during its “cold martensite state” and would return, unfold or extend to its memorized shape of bigger sun-fa-cing area when the temperature due to the sun rays reached a specified point. (X degrees celcius set by the constructor). Basic problems of this design would first of all be the enormous amounts of shape memory material needed to cover a whole façade of an office building (or any other large building), given that the cost for such materials is still high. However the most important problem seeking for an effective solution is that in this example shape changes only ONCE.

Constant shape change and use of shape memory effect in the project.

As already mentioned the use of a self transforming shape memory sheet as a shading unit has many disadvantages and would also be very expensive both in real life and in this specific project. At this point the decision was made in favor of the use of a shape memory alloy only as the driving force for the sunshade system. High efficiency, self adaptability and adjustability would be absolutely preserved while at the same time only small quantities of the alloy need to be used.

This means that not the actual shape change but the forces exerted during the transition from one shape (cold) to the other (warm) will be the main factor for the operation of the façade unit.

One basic question however remains:Shape memory alloys have only one shape memory, not two. How is the system going to adapt to constant changes if only transition from cold to warm activates the shape memory effect and not the opposite transition? (see figure)

The opposite direction, would in this case never work. The device would be installed on the façade and only move to its memorized austenitic structure/shape once, when temperature ex-ceeds the specified transition point. The original (stable) shape of a warm shape memory alloy will not change into any other shape on its own when cooled down, so even when temperature becomes lower the shape will remain the same.

Figure 21.1: shape memory alloy as deforming sheet

Hea

ting

up

?

Figure 21.2: one way deformation of memory alloy. Solution for opposite direction has to be found

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The answer to this question is that a certain reaction force has to be exerted on the shape memory alloy. This force will deform the material when temperature is below the transition point and the shape memory effect will bring it back to the original shape every time temperat-ure exceeds the transition point. This can be visualized by keeping in mind all the experiments with nitinol, where someone always heats up the deformed alloy to show the shape memory effect, but will have to use its own force to deform it again in cold conditions as it will not deform under cooling. The idea of a reacting force did of course not mean that the requirement for zero energy usage would be overlooked. The needed reaction force had to be precisely calculated through exper-iments and then found through a force already existing in the structure (weight) or by other no energy consuming parts (preload, springs etc) .

Implementation and design

Rhombus and nitinol

The basic unit of the shading system would be the rhombus shape. A long lasting development and research process led to this elementary structure that started as an inspiration from the braided tube structure of medical stents. Forces exerted towards the corners of the rhombus along its diagonals have an impact on the opposite direction and can create shapes with a dif-ferent area, ranging from a perfect rectangle (biggest area) to a very slender shape that tends to be a line (smallest area). (see figure)

In a braided system or grid of connected rhombus shapes, forces along the diagonals of a rhombus affect more than one units. If one or more shapes become wider, then the overall grid will become wider, or, if it is limited to a stable frame, the neighboring shapes (rhombuses) will become narrower due to the same forces. This complex problem needs more research and experiments to be effectively implemented into a project. One solution could be to allow the grid to extend to parts of the building that are not transparent, and thus will not be affected by a denser or more transparent grid layer. To be able to accurately measure forces, move rhombus units with precision and have an independent adjustment of each unit the final system com-prises separate rhombus units within a non moving grid frame.

Description

The rhombus unit consists of four 230 mm long metal rods/bars of rectangular section ( 3mm thick, 20mm wide) connected with four hinge joints placed at the ends of the rods. The surface inside this metal shape is covered with a thin flexible fabric that prevents the sunlight from en-tering into the building (this fabric can also be semi transparent if more light is needed). The metal rods can freely rotate around the joints that comprise a plastic low friction spacer ring, an m4 bolt with a smooth (not threaded) upper part and a safety nut at its end. Relatively low fric-tion is important in this design, especially for the project’s model (not that much in the real life design) because forces are lower and calculations may not be accurate enough if friction has to be separately calculated for each case. All rhombuses are attached to a wooden or metal grid (wood used for the model). The grid is the basic frame on which the shading units are hung and which will afterwards be attached to a building façade. The frame consists of rhombus/rectangular shaped gaps/holes that allow the sun rays to pass into the inner space of the build-ing. These gaps have the dimensions and shape of the folding metal rhombus which hangs from the frame and covers the gap at different percentages, from 100% (completely covered) to only 25% according to how folded or unfolded it is.

Figure 22.1: extension of the spring

15 cm4 cm

KG

15 cm4 cm

KG

15 cm4 cm

KG

15 cm4 cm

KG

Figure 22.2: Part of force calculation

Figure 22.3: Possible reaction forces and motion

Figure 22.4: rhombuses in different planes to allow movement without collision.

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All the units hang from their top hinge joint which is the only point the unit is actually connected to the frame. (there is also a rail for the bottom joint which however only makes sure the move-ment is precisely on the vertical axis and that possible windload would not cause problems). This decision was connected to the selection of self weight as a reaction force that would make the rhombus move together with the shape memory polymer. Hanging from the top joint the rhombus’ self weight helps it fold into a slender shape.

Other solutions with more rails or unfolding to other directions for design reasons did not fulfill the requirements. They also required finding another reaction force which would then probably be a preloaded spring force. This solution will be analyzed at a later stage (“motion” chapter).

For the design of the hanging rhombus there was however still one problem. During the mo-tion between completely folded and unfolded state the elements were colliding/interfering with each other, especially when not all elements were moving to the same extend. The folding rhombus becomes longer in the y-axis, which means that it will hit the one underneath it. Put-ting each rhombus in another plane by moving them perpendicular to the façade (more to the inside or to the outside) also causes problems as the top joint of each unit needs an axis/shaft to attach it to the frame (see figure). The problems also concerns shading units neighboring diagonally (not only in the vertical axis), as they would also interfere under certain conditions. Diagrams and experiments first led to a solution of a frame that has the shading rhombuses alternately on its external and internal side to avoid colliding. However a simpler solution was finally chosen. The two lower rods are bent at a specific point to move within another plane in order to ensure clearance with the other ones (see figure).

Motion and driving force

The way the rhombus would fold and unfold from a perfect rectangle covering the whole space behind it to a very slender shape that allows sunrays to pass into the building is, as already ana-lyzed, based on the properties of a shape memory alloy, nitinol.

Transition from one shape(folded) to the other (unfolded) will happen in response to temperat-ure change. Choice of the proper mixture between Nickel and Titanium makes sure the trans-ition temperature is best suited to the specific environment.

Force on the rhombus will be most effective if exerted on the corners/joints. (Proven by exper-iments and calculations). The shape memory alloy will best work in tensile forces as a design pulling two corners/joints close to each other is much more effective (less material needed, even a thin wire could work) than one pushing two corners away from each other and does not need support to avoid buckling etc.

One of the strongest and most effective (less material) structures for this application are tension springs. As a result a nitinol spring has to be used to exert tensile force on two opposite lying rhombus hinge joints. A tensile force can only be created in this case if the alloy remembers its “short” spring shape (original shape). As previously explained a shape memory alloy of this kind can only exert force (move) during its transition from cold/martensite state to warm/austenite state. This means that the only way to use the tensile force of a shape memory spring in this design is by connecting the top and bottom corner joints of the rhombus. Heat above the transition tem-perature will thus make the spring shrink and pull the two vertical corners closer to each other. The top hinge is attached to the frame so it will actually raise the bottom of the rhombus until it reaches the perfect rectangle that covers the whole gap.

Figure 23.1: rhombuses put alternately on different sides Figure 23.3: three different layers of rhombuses

Figure 23.4: different size rhombuses Figure 23.5: connecting a row of rhombuses to move them at once

Figure 23.2: rhombus lower part bent for overlapping

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Experiments and Reaction Force

It has been practically very difficult to experiment with the actual weights and nitinol springs that would be used in a real façade. The entire design of the built model had to be adjusted according to the properties and dimensions of the material that was most difficult to find. Of course these were the Nitinol tension springs. They were chosen to have a reasonable range of length and force but it was difficult to order them with transition temperatures low enough to work just with the sun heat and with forces exactly matching the weights of the materials we could easily use/cut/drill within the course.

Most common nitinol springs for sale have a transition temperature between 40 and 60 de-grees celcious. However findings can be easily used for lower temperatures as the forces, effect and principle is exactly the same if only the temperature specifications change and not the dimensions.

Starting with a more theoretical part, the movement of the final shading device does not only make use of the shape change of nitinol, literally speaking, but of the thermo-variable spring rate of a nitinol spring (which of course is connected to its shape change). Spring rate is the amount of weight needed to compress/elongate a spring by a certain distance (N per mm for instance) (see figure). Being thermo-variable means that the nitinol spring has very different stiffnesses according to temperature. A tension spring with a short original “memory shape” will have a much higher spring rate (be much stiffer) when hot (original-short condition) than when cold. This characteristic of shape memory springs is a big advantage for the sunshading system. An (almost) constant force of X magnitude may be enough to keep the spring elongated when it’s cold, and at the same time not be enough to prevent it from shrinking when it is hot (or strong/stiff according to theory), which is exactly what is needed. This remained to be proven by the experiments with weight (constant force) and regular springs (linear but not constant force!).

Experiments started with heating and cooling the nitinol spring, to get an idea of how fast the shape transition happens, what the fully extended (until it starts to show fatigue or permanent deformation) and fully shrunk length is and how it reacts to temperatures very close to the transition temperature. (45 degrees in this case) Shape change proved to be much faster than expected when temperature significantly exceeds the transition temperature. Flow of hot air or water also works much better than hot objects touching the spring, even if their temperature is much higher. Lengths of the spring ranged from 40mm when hot to almost 150mm when cold elongated by hand. These 110mm of difference between the hot and cold condition would later be part of the calculation for the rhombus diagonal as the diagonal length difference from the rectangle shape (short diagonal) to the slender/thin folded rhombus (long vertical diagonal) had to be exactly that difference of 110mm. Temperatures very close to the transition temperat-ure caused only slight move of the spring but just a few degrees more were enough to make it slowly shrink to its limit. This would later be much improved (much better/wider range of slow deformation according to temperature) due to the reaction force (weight) and the change of spring rate when heated/cooled.

Figure 24.1: load-displacement graph nitinol

Figure 24.2: nitinol spring against steel spring (thermostat)

Figure 24.3: experimenting nitinol spring with weight Figure 24.4: experimenting nitinol spring with elastic band

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Heat from the sun rays heats up the spring, which when cold is elongated to allow a very slender rhombus shape. The spring shrinks in response to heat and makes the shape of the rhombus a rectangle that closes the gaps of the façade.

The previously mentioned question still exists. Which is the reacting force to deform/elongate the nitinol spring again and bring the rhombus back to its slender shape when temperature drops?

While this question could be generally answered with “weight” or “a counter spring”, many experiments and calculations were needed to precisely find out which solution would actually work (see figure).Another side effect of the lack of a reaction force was that the transition would be relatively fast and only within a very small temperature range, as the wire would usually be in its fully extended or fully shrunk position.

More experiments were made to observe the reaction force needed to pull the shrunk nitinol spring back to its elongated condition. Is it a constant force or not? Would a counter spring work? Experiments included hanging certain weight from the spring and precisely adjusting it, as well as connecting the nitinol spring to regular springs. To observe the motion of the sys-tem the nitinol spring was heated and cooled alternately to change its stiffness and shape. If a certain constant weight worked better than a counter spring, it would mean that the simplest solution could be chosen. Weight of the entire rhombus would be accurately calculated and adjusted to exert this specific force on the spring. In case the counter spring worked better, such a spring could be used to connect the other two (horizontal) hinge joints (see figure).

Experiments showed that for this specific nitinol spring 700g of constant weight worked per-fectly. The nitinol spring was strong enough to raise 700g to its fully shrunk condition when heated well above the transition temperature and 700g were heavy enough to deform/elong-ate the spring to its longest shape of 150mm when cooled (spring rates becomes lower, spring becomes softer). The findings of this experiments were very important for the project as they led to the simplest solution. In the real sunshading mechanism self weight of the rhombus would be enough if precisely calculated and adjusted, to move from its folded to its unfolded state only under temperature change without any other power supply or even spring. Weight has to be adjusted according to the spring force but also the other way around works. If the shading element has a predefined weight, a nitinol spring with certain -specific- dimensions (able to produce a specific force) has to be chosen for good operation/motion of the sunshade.

The findings of tests with counter springs (or elastic bands) on the other hand were difficult to decrypt. Linear springs are springs giving a straight line force/elongation diagram. The more the spring has to be deformed the more force (analogically in linear springs) is needed. The consequences of these properties on the existing structure were the following. When choos-ing a regular spring soft enough (lets assume 700g of reaction force only at its fully elongated position) to allow the nitinol spring to reach its highest/fully shrunk position it would not be strong/stiff enough to pull it all the way back when it is cooled down, because shrinkage of the regular spring means reduction of its counter force. On the other hand a strong/stiff spring (lets assume 700g of reaction force only at its shortest position) will succeed in pulling the nitinol wire down to its fully extended position when cold, but will be way too strong to be elongated until the nitinol reaches its shrunk position, considering that forces become bigger and bigger according to Hooke’s law.

Figure 25.1: expirement with nitinol spring and bottle of water. Adjustment easy by adding water to precicely get the needed reaction force

Figure 25.2: Use of sandbags as reaction force. Precise adjustment of weight possiible. Relatively small volume

Figure 25.3: Elongated nitinol spring by additional weight

Figure 25.4: melted led in candle housings

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At this point just for collecting more information and alternatives an additional search for con-stant force springs that do not obey Hooke’s law began. Springs that produce practically con-stant force are usually designed as rolls of high yield stainless steel stripes which are at their relaxed state when rolled up and exert an almost constant force when unrolled. The easiest way to find them seemed to be just destroying some measuring tapes. (the ones that roll back when released). Using two relatively strong ones (needs to exert 700g on the lower joint of the rhombus) attached at the two horizontal hinge joints of the rhombus and connecting them does almost work as good as weight (constant force), although it is too much complexity and more points prone to failure under operation.

Final Design

Development of the system finally led to a relatively simple mechanism using the principle of shape memory and change of spring rate of a nitinol spring actuated by temperature change. The “counter effect” is achieved by the self weight of the structure.

The stainless steel rhombus comprising four rods connected with four hinge joints at their ends and an elastic semi transparent fabric (percentage can vary) between them, can move from a fully folded elongated slender shape to an unfolded rectangular shape. The rhombus hangs from its upper hinge joint which is connected to the basic supporting frame (see figure). The lower joint moves within a rail that ensures that the system is stable and moves accurately on the vertical axis. The frame being exactly behind the hanging rhombuses has holes of exactly the same size and shape of the rhombus in its rectangular shape (fully unfolded), thus letting more or less sunlight enter the building according to the position of the rhombus unit.

Movement of the basic rhombus unit between the two extreme positions to shade more or less, is achieved by the tensile forces of a Shape Memory tension spring attached to the top and bottom joint and by the reaction force provided by each rhombus units self weight. Due to properties of the shape memory material Nitinol the spring has a higher spring rate when warm (above a certain temperature set according to the needs) and tends to return to its short shape, thus prevailing over the constant weight of the structure. This forces the rhombus to unfold to its rectangular shape and shade more as the vertical diagonal shrinks. When on the other hand temperature drops under the specified transition point the nitinol spring becomes softer (spring rate drops) and the constant weight force of the structure prevails over it, deforms it and forces the rhombus to fold into its elongated slender shape that let more light enter the building.

Use of the sunshading system on a real building

After a long period of development on a theoretical basis and working on experiments for sep-arate parts of the final design the basic question of “how this system could be integrated into a real building’s façade” remains and needs to be answered. Although some aspects related to no use of energy, smart materials or adaptability were extensively investigated to guarantee that is an actually effective and innovative system, the structure does of course need further development to be sustainable, not too expensive and as simple to maintain as possible. Draw-backs and possible points that need improvements will also be described.

Figure 26.5: 3d rhombus facade detailFigure 26.4: external facade view

Figure 26.3: section facadeFigure 26.2: front view facade element

Figure 26.1: motion of rhombus closing

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Adaptive to the outer or inner climate?

Beginning with the integration of the system to a façade one has to consider if operation of the sun-shading mechanism will create a shape transition according to external or internal space temperature. The first case shades more or less collecting data from the environment and the system is placed on the outer layer. The operation is not always very precise according to the needs as it does not react to sunrays or light, but to temperature. This makes it possible to have insufficient shading when light is very strong but temperature relatively low, or too much shad-ing when the opposite happens. A system to concentrate sunrays (like a small lens or parabolic mirror) on the shape memory alloy to ensure that it heats up faster than the environment was considered too complex, expensive and dangerous (fire) to develop at this stage.

Using the structure as an external layer also means that all moving parts need to be regularly maintained to ensure good operation even if weight of each element is enough to not depend on additional friction created on the joints due to rain, dust etc. It also has to be precisely con-structed and assembled to avoid noise under windload and operation.

Before considering the adaptability to the inner climate there is one more option of placing the sunshading system in a closed intermediate space, again collecting “data” from the sun intens-ity that heats up the space. To protect the system from high windloads, rain and wear of moving parts it seems also from this perspective a better solution to place it within a cavity/double skin or behind a first glass layer,partly separated from the inner space.Temperature that the shape memory alloy will sense is in this case more accurate and closer to the real needs of the internal space.

In the third alternative the shading structure is seen as a possible solar heat gain controller, by letting sun in to heat more or less the inner space according to the temperature needs. Shape transition is in this case actuated entirely by the inner climate/temperature. When the building heats up beyond a certain transition temperature the sunshades close to protect the inner space from overheating due to the sunrays. On the other hand when internal temperature drops below the specified point the sunshades fold again to let more sunlight heat the space.

Uploaded Videos of Sunshading system and experiments:

http://www.youtube.com/watch?v=TfIbBP4Lp7w

http://www.youtube.com/watch?v=fcmPhSfZFtM

http://www.youtube.com/watch?v=2SfHikipyfw

Figure 27.1: impression facade on building

Figure 27.2: impression facade from inside

Figure 27.3: rhombus detail

Figure 27.4: impression facade part with floors

Figure 27.5: elevation facade from inside

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Conclusion

Important advantages like no need for any connections, motors, actuators, control units, power supply, complicated or time consuming on-site installation procedures/adjustments by techni-cians, have all been already described and comprise the main reason for describing the mech-anism as an efficient one that is worth developing and improving.

However some drawbacks and possible points prone to failure have to taken into considera-tion. One important drawback is that the system has to be more developed to be adaptive to the actual sunrays and not only temperature. Whether it is used as an external layer or within an intermediate cavity it will according to the existing design only react to temperature change caused by the sun. The fabric that has to be used within the rhombus is also a part that needs further investigation. It has to be very flexible and at the same time not interfere with the operat-ing system or buckle too much. The springs themselves are also a point to consider as fatigue of metals is always a problem with constant elongation and shrinkage. Nevertheless Nitinol due to its hyperelasticity properties and atomic arrangement shows much higher resistance against fatigue compared to any other regular metal.

Evaluation

Within this project some compromises had to be made due to limitations. These may at the end have consequences on the accuracy of the model in relation to the real structure, but showing the principle and basic operation of the system was the main priority.

It has not been easy to find the shape memory alloy with the exact properties to match the desired temperature and the weight of the rhombus unit. The system had to be constructed according to the specifications of the springs that were at that time available on the market for a reasonable price. The spring imposed specific, relatively small dimensions for the rhombus. These dimensions were about 230mmX20mmX3mm for each one of the 4 rods which had to comprise a structure that would exert 700g of force on its diagonally attached spring.

Calculating with the densities of different metals for these dimensions, only very thick stainless steel or lead would reach the desired weight to make the system operate by its own weight as it would on real building facade. Stainless steel of the calculated thickness was a difficult ma-terial to cut, bend and drill in the building week of this course and lead was also a material with properties that would not help the team with the construction. The only metal that could easily be bent, cut and drilled in the courses workshop was aluminum, which unfortunately is a really light material. This led to adding/hanging additional weight from the bottom joint of each rhom-bus to simulate the real weight of the structure and provide a reaction force for the springs.The simple solution of hanging sandbags from each rhombus lower joint was used. However seeking for very small and heavy parts (high density) also solutions with lead came to mind. After melting some spare plumber parts in cylindrical aluminium candle casings (calculating density of lead and volume of the candle light it was easy to find the exact weight) with a central hole for attaching to the lower joint, it was found that these lead parts could be a good altern-ative for the model.

Of course more time and machines would make it easy to either find a softer or longer spring, or construct a heavier rhombus of real 1:1 size and weight from the beginning. Calculations and experiments have showed that it is not a difficult task to make the system work with the rhom-buses own weight.

Figure 28.1: facade with closed rhombuses

Figure 28.3: model photos

Figure 28.2: facade element 1090x1090mm

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Bibliography

“Smart Materials in Architecture, interior Architecture and design” Axel Ritter“Thermovariable rate springs” Stoekel Waram, The magazine of spring Technology“Materials, engineering, science, processing and design” Ashby M., Shercliff H., Cebon D. “Engineering Aspects of Shape Memory Alloys” Duerig, T.W., Melton, K.N., Stöckel, D. and Way-man C.M.

Shape Memory Facade

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Transcript of Shape Memory Facade