C O C O O N
A R C H I T E C T U R E
Exploring the structural potential of Attacus Atlas cocoons on an architectural scale.
A dissertation submitted in partial fulfillment of the degree of BA in Architecture 2018 150399953 Tutor: Martyn Dade-Robertson Module: ARC3060 Dissertation in Architectural Studies Word count: 8400
A C K N O W L E D G M E N T S I would like to thank the Head of the Bio-Materialism Dissertation elective - Martyn Dade-Robertson for the valuable guidance and encouragement received.
T A B L E
O F
C O N T E N T S
Introduction Basic forms of shelters Shelters in larval insects and their advantages Dissertation’s aim
1-5 1 2-4 5
Chapter 1: Case studies
7-15
Silk Pavilion by MIT Media Lab ICD/ITKE Research Pavilion 2014-15 of University of Stuttgart
7-9 11-14
Chapter 2: Attacus Atlas
17-23
Background information about the species Personal rearing experiment Cocoon analysis Chapter 3: Application on an Architectural Scale 3D studies of a cocoon Leaf as a foundation Final 1:50 model and evaluation
17 18 19-23 25-37 25 26-28 29-37
Chapter 4: Material Properties of Attacus Atlas Silk
39-43
Behaviour of fibres compared to other insects Behaviour of fibres in water Suggestions of materials based on the above and additional case studies
39-40 41 42-43
Conclusion
45-46
Bibliography
47-48
List of Illustrations
49-50
I N T R O D U C T I O N For the purposes of hunting and harvesting, our ancestors had to design and build temporary, but functional shelters. This would require, even basic, but some forms of engineering and construction by utilizing natural and locally available materials. The early form of tents, for example, featured less of the actual structural frame, but more of the tensile elements like animal skins or woven animal hair (Horning, 2009). Most commonly, to support the tensile structure, the presence of a vertical support is needed, whether it is an internal frame that is built from scratch or an external frame such as trees that already exists (Fig. 1.1 a, b) (ibid).
Just like us, many insects build their simple shelters externally by covering, tying, folding or weaving plant leaves with their own fibres (Weiss et. al 2004). In their case, they are using leaves as a structural framework with their silken layers acting as covers instead of animal skins in our scenario.
Fig. 1.1 a
Fig. 1.1 b
The other types of early dwellings included tipi, kathe and yurts, but the questions that arise are, were humans the first ones to come up with such strategies and was it achieved in the best way possible?
Shelter construction may kick start at the sides of the leaf or in the centre and may involve a small segment of a leaf, a whole leaf, or more than one leaf (Lind et al 2001).
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The most adaptable shelter type on the macro scale is, yet again, a simple tent. Leaf tents are the constructions that insects make by cutting fragments of leafs with their mouth-parts and then folding it over and in most cases, attaching to the main leaf with silken fibres (Fig. 1.2) (ibid). Larvae stay under this “shelter� for the period of their development feeding on the parts of the leaf under the tent for the purpose of protection from predators and harsh climatic conditions.
The Epargyreusclarus Cramer are master builders that are able to construct five different shelters during the development of organisms (Lind et al 2001, Weissetal 2004). Amongst the family of insects that comprises of butterflies and moths, approximately 24 species are reported to build shelters from leaves and the most talented engineers can be found within the family of small moths (Lill & Marquis 2007).
Fig. 1.2
Some insects, such as the skipper Epargyreusclarus Cramer of Lepidoptera family abandon their constructions after they develop from larvae while we tend to stay in ours for as long as we want unless, for example, the occupancy increases or environmental conditions change.
Based on this information, it is safe to say that many larval insects and especially those of Lepidoptera species have similar construction techniques to humans when it comes to tensile structures and the main difference is in scale and materials.
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Other insect species build nests (Fig. 1.3) using either surrounding materials or self-produced substances to raise their offspring within the nests (Hansell 2005). Wasps, for example, construct paper-like material to build their hexagonal cells by chewing wooden fibres and mixing it with their saliva (Tautz 2014). Their nests can vary greatly due to different types of wood that can be used, yet their main purpose is to protect offspring from the unfavourable effects of the biotic environments such as natural enemies and abiotic environments namely unsuitable environmental conditions (Hansell 2005).
Overall, the mentioned insects can rival us in their great skills and thinking in design and engineering, but the big difference is between the resilience of those structures made by insects and us. By the term resilience, I mean the structures that can recover quickly after experiencing challenging circumstances such as bending or compressing which can happen as a result of both biotic and abiotic environments.
Fig. 1.3
The former has a very strong impact on the design and engineering of nests because a failure to build a shelter that can camouflage well with the latter may result in a reproductive failure (e.g., Ricklefs 1969; Fowler 1979; Strassmann et al. 1988). Therefore, wasps cleverly build nests with different patterns and forms to protect their offspring from predators.
For example, if a spider’s web (Fig. 1.4) is being stretched, the whole structure will not collapse except the light damage done to the fragment that has been challenged which can then be quickly repaired by the spider (Fig. 1.5) (Asakura and Miller, 2014).
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The unsolved mystery lies in the reasons behind such high damage tolerance and whether it is related to the silk properties of spider webs. In order to test the web tolerance, certain segments of webs were removed and a load was then applied to understand that indeed, even if some large fragments of the web are removed, it can still perform just as well with only a minor decrease in load-bearing capacity (ibid).
However, there are a few issues that need to be considered and the most problematic one when it comes to learning from nature is scaling up: what works on a small scale may not work on a larger scale. As perfectly described in (Knippers et al. 2016) a project inspired by a tree may not work because of inadequate properties of materials or the loads a tree can withstand compared to the ones required for an architectural project.
Fig. 1.4
Fig. 1.5
The man-made structures, on the other hand, do not possess such qualities because even if we take a simple tent as an example, with the removal of certain segments its load-bearing capacity will decrease drastically.
In order to make a tree-inspired structure to work, more research and investigation needs to be done regarding various factors that make trees “work� other than resembling a tree visually (ibid).
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Another thing to note about larval insects is their efficient use of material: an insect only uses as much material as needed for the construction of its shelter compared to us, humans that waste large quantities of material during the building process (S. F. Aaron, 1923). However, the main reason behind this phenomenon is the ability of the insects to produce the material within their bodies, which on a human scale is not implementable. The resilience of the insects’ structures, on the other hand, is something that we can transfer to the design and construction process.
The following chapter will introduce my subject namely Attacus Atlas or more commonly referred to as Atlas Moth covering the background information including their life cycle. Then, I will report on personal experiments conducted to grow and observe the process of making a chrysalis by rearing moths in home conditions covering the failure of it, the reasons behind the failure and what was learned from it. The following chapter will cover the cocoons of the Attacus Atlas talking about the manufacturing process and structural analysis. The next chapter is aimed at the application of the moth’s behaviour on structural design and proposing a potential implementation on an architectural scale. The final chapter is going to cover the structural properties of the silken material used by Attacus Atlas and suggest alternatives.
Resilience is a crucial element that most traditional networks must comprise of in addition to many other components (Vlacheas et al. 2013). In simpler words, resilience is a quality that a network needs to continue operation, even if some failures occur. In larval insects, resilience is achieved through the complexity of layering and weaving in their constructions. In my dissertation, I am going to be observing the behaviour of one such insect - Attacus Atlas due to their very interesting and unique cocoon weaving technique that is very strategically phased and results in very resilient structures. The first chapter will cover the architectural case studies that have allowed weaving insects to drive their design and sometimes, manufacturing process. The chapter will cover the challenges that were faced and how they were eventually tackled on a large scale.
My dissertation’s aim is to prove that Attacus Atlas are very skilful creatures that can be used by scientists and architects in ways other than the mass production of fabric and that a biomimetic approach can and should be utilized by humans without necessarily having an access to sophisticated software.
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C H A P T E R
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C A S E
In this Chapter, I am going to cover two architectural case studies that have successfully implemented the fibre-based approach in their projects.
S T U D I E S
“The Bombyx mori silkworms can be characterized as ‘multi-nodal spinning organisms’ because, without much of interaction, they can adapt extremely easily to the surroundings with regards to their environmental or spatial factors” (Oxman, 2014).
Even though biological organisms can be used for many purposes namely the production of fuel and cancer treatment, there is not much research targeted towards their applications on a larger scale such as product or architectural design (Oxman, 2015). However, some practitioners such as the team at the Massachusetts Institute of Technology and Achim Menges managed to produce very advanced and promising projects based on the detailed research targeted towards insects’ behaviour.
The species are capable of spinning a one-kilometrelong thread of silk in 72 hours to form a cocoon (ibid). In order to motion-capture a silkworm, a small magnet was attached to its head (Fig. 2.1), which recorded the movement with the help of three magnetometers placed in the box. The data was then converted into a visualisation (Fig. 2.2).
The first one is a pioneering example called the Silk Pavilion, which was developed by the Mediated Matter Group at the MIT Media Lab. It explored the collaboration between technology and biology in the form of robots working with silkworms to design and build the pavilion.
Based on the observations (Fig 2.3), the silkworm needed at least 21 mm high pole or a room with 21 mm tall “walls” to spin a cocoon-like structure. Below this height, only tent-like canopies were spun and, in the absence of any pole, a non-enclosed surface patch was spun. The density of silk varied depending on the distance from the central pole with fibres on the surface boundaries appearing to be denser. (Gramazio, F. 2014)
Fig. 2.1
Fig. 2.2 7
Fig. 2.3
Due to the constraints of current CAD tools, a new parametric environment was created to provide a constant iteration between a digital modelling and physical manufacturing process. Additionally, it allowed real-time examination of several design solutions (ibid). The aim was to determine the space for every digital silk fibre within which a silkworm can spin to allow the transfer between the digital and biological fibres. Finally, it was important to figure out the geometry and the scale of the pavilion as well as the temporary scaffolding arrangement. The parametric environment was developed on top of the RhinoCommon Build, which operates on Grasshopper plug-in. It allowed the formation of lightweight fibrous elements due to the programmed set of routines (ibid).
The gathered data informed the thread pattern as well as the spherical shape that consisted of smaller hexagonal patches (Fig. 2.4). Another challenge was to, based on the biological properties of silkworms, supply the maximum silk deposit reach (ibid). The site’s lighting properties determined the size and placing of each aperture (Howarth, D. 2013) and for each of them, the computational protocol generated an extended tangent circle - a hollow circle within the patch that was formed due to the programmed pattern of the thread (Fig. 2.5). Then, the circle was turned into tangent line sectors that matched the representation of the patch and for each such circle, a resolution-controlling parameter of tangents was set (Gramazio, F. 2014). The parameter identified the proportion of the individual fibre gradients to the total allocation of fibres.
Fig. 2.4
Fig. 2.5 8
Finally, the algorithm checked if apertures were contained within a single patch, many or none and for each patch that contained a whole or incomplete aperture it generated five elements:
The aluminium structure itself was first constructed by connecting all the 26 frames and then folded into a sphere (Oxman et al. 2013). The frames were manufactured with hook elements featuring release mechanisms (Fig. 2.7) that have allowed the frames to be easily taken off after the weaving was complete and the structure was tensioned within the space. Between the connecting corners of each frame was a little piece of piano wire covered in rubber to which the nodes of the frames were attached (Gramazio, F. 2014). The nodes served as a guide to make the structure stable within the space when panels were removed.
• The aperture development in correspondence with the thread pattern • The distribution of thread across apertures • Contour attachments • Scaffolding design based on the weaving patterns of silkworms • A path for the CNC robot.
Fig. 2.6
Fig. 2.7
Later on, the temporary aluminium frames in the shape of polygons were designed to resemble the patches (Fig. 2.6). Based on the data collected from the observations and protocols the CNC robot was generated to mimic the behaviour of a silkworm. The machine consisted of the wedge to carry the replaceable thread rolls, the spindle, the tube that sent the thread to the tooltip and a rotating shaft that moved alongside the machine (Gramazio, F. 2014). The ultimate advantage of the thread as a weaving material was its lightness as it allowed the machine to weave at a very high speed.
When the structure was formed and the panels were fixed, the sphere was lifted and placed where needed. After the removal of the aluminium panels, some tension, however, was lost leading to a further tension between the suspension lines of the pavilion (ibid). The lower part of the structure was attached to a circular 25 mm thick MDF covered in white vinyl (Fig. 2.8) (ibid).
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Fig. 2.8
After the structure was tensioned, 6500 reared silkworms were placed on it to start spinning (Khan, S. 2013). The majority of silkworms were found to stay in a specific part of the surface spinning in circular motions or eventually move to the highest surface patch of the dome (Howarth, D. 2013). The latter might be due to the higher temperature, lower illumination rates and decreased amounts of energy (ibid).
After three days of spinning, the silkworms were collected from the dome and continued their life cycle as moths (Gramazio, F. 2014). Overall, the final structure consisted of 15,132 metres of digitally fabricated thread and 6.5 million metres of a biologically spun silk (Oxman 2014). The complex weaving in addition to it being tensioned within the space has allowed the structure to be quite resilient because the biological silk did not only act as an additional skin but also as an adhesive. 10
The experiment has proven that a corporate silkworm spinning is an applicable strategy to design a very mobile structure and may have many potential applications in the future when it comes to using insects as builders in swarm construction (ibid).
One more example of the biomimetic design approach inspired by insects is the ICD/ITKE Research Pavilion 2014-15 of University of Stuttgart that demonstrated a different behaviour of the CNC machine. The robot, in this case, was programmed in the way that allowed it to obtain the information from its environment and establish its own manufacturing pattern (Thomson et al 2015). This led to stabilising a fragile at first structure by applying more fibres on the inside until the shell became firm enough to allow the transformation of the pavilion’s aerial envelope into its skin. During the day (Fig. 2.9), the carbon fibre skeleton is only slightly visible due to the reflectiveness of the outer skin, while during the night (Fig. 2.10) the interior illumination displays the stark visual contrast between the two elements (Schumacher, 2016).
I found it quite exciting and inspiring that the project managed to successfully apply observations from nature on to the design by also utilising the insects themselves during the construction phase.
Even though in my dissertation, I am exploring the influence Attacus Atlas can have without the participation of the moths during the building process, I found the structural hierarchy of the pavilion very intriguing. For example, the use of primary, secondary and tertiary structures here is quite unique; the aluminium panels, even though being temporary, do the job of a primary structure, with the robotic thread weaving being the secondary structure followed by the biological silkworm fabrication as a tertiary element.
Fig. 2.9
However, after the removal of the aluminium panels, the surrounding environment of the pavilion becomes its primary structure. I find this incredibly exciting because it refers back to the silkworm’s behaviour where the conditions of the surrounding environment such as a height of the space or a pole affect the construction possibilities of the cocoon.
Fig. 2.10 11
The research was targeted towards observing the way the diving bell water spider (Argyroneta aquatica) constructed its air bubble nest (Fig. 2.11) to develop a strong yet light structure by combining robotic fabrication with a computational design. This unique project took one and a half years of thorough research and experiments undertaken by professors and students of natural sciences, engineering and architecture at the University of Stuttgart. (Knippers et al. 2016)
In order to successfully translate the biological behaviour into a fabrication process, air bubble construction and its’ reinforcement with silk fibres of ten spiders were observed by the ICD/ITKE team (Thomson et al. 2015). The recorded photographic and video data was then carefully analysed and the behaviour pattern was identified (Doerstelmann et al. 2015). First of all, the stage where the arachnid constructed the exterior web to hold the diving bell could not be transferred into the design process because of the ever-changing geometry of the bell; hence, the phases of the interior web building were investigated (Thomson et al. 2015). The main reinforcement of the diving bell takes place from the inside, which helps the protection from predators and the air supply. This was translated into the digital fabrication with the robot applying carbon fibres on to the interior of the membrane that helps to protect both the fibres and the machine from the abiotic environment (ibid). Additionally, based on the visual analysis of the spider’s behaviour, the idea of using the membrane as an external envelope emerged. This allowed the structure to be stable with only the reinforcement of the membrane via the carbon fibre framework with no additional structure needed (Doerstelmann et al. 2015). (Fig. 2.12)
Fig. 2.11
Unlike most of the arachnids, the diving bell water spider spends most of its time underwater and in order to survive, it builds a strengthened nest by regularly sticking its abdomen out of the water to capture some air bubbles in between its hair that it then uses to form an air tank trapped with silk (Doerstelmann et al. 2015). The most astonishing thing is the efficient use of fabrication that allows reinforcement of the air bubble from its interior by numerous silk weaving actions, which form a resilient airtight structure (Neumann and Kureck 2013, pp. 1–5). However, the insect faces many challenges underwater that might be too ambitious to tackle on an architectural scale.
Fig. 2.12 12
The most challenging part was finding the appropriate materials and to program a fabrication pattern that allowed an application of fibres against the gravity. To solve this problem, the material of the membrane had to be stiff enough in order for the machine to apply the form-work with no distortions of the membrane caused. Additionally, the material had to be transparent and UV resistant. Following multiple tests, a 0.2 mm thick Ethylene Tetrafluoroethylene was selected as the material for the membrane, while the carbon fibres contained 48,000 filaments filled with epoxy resin (Thomson et al. 2015) (Fig. 2.13). In order to achieve a stable structure, several fibre application strategies had to be tested with multiple types of adhesives and surface treatments.
The fibres were placed on the inside against the gravity with a custom designed and built effector that incorporated an online control operating on sensors (Doerstelmann et al. 2015). Surprisingly, even though fibre application requires a fibre tension, the tension between the fibres and the membrane had to be lowered to prevent fibres from coming off; hence, an extruder mechanism was designed (Thomson et al. 2015). The last problem was the dead load of the untreated carbon fibres that had to be hardened and held together with an adhesive (ibid). It was critical to apply the correct amount of adhesive and to distribute it evenly, which was accomplished by a mechanical sprayer on the effector.
In order to implement the project on site (the campus of the University of Stuttgart), the robot had to be specifically programmed to apply the fibres so that it does not deform the ETFE membrane. The main difference between the behaviour of the water spider and that of the machine is that the former can apply silk fibres randomly at any point in the bubble while moving within it. The latter, on the other hand, is placed strictly in the centre. In addition, the robot is restricted in its reach and first axis (ibid). To make the double-curved ETFE membrane, it was first supported by the air pressure and then divided into segments that were flattened (Doerstelmann et al. 2015). To prevent plastification during the fibre reinforcement process, the stress to strain ratios were tested and analysed as well as the carbon properties of the fibres themselves (Thomson et al. 2015).
Fig. 2.13 13
The primary fibrous structure consisted of crossing carbon fibre threads which acted as beams. It turned out to be very strong yet light weighing only 260 kilograms (Doerstelmann et al. 2015). This was achieved by testing different load bearing systems in relation to the material properties of the fibres (Fig. 2.14). The final load-bearing system was resistant to buckling and stiff due to the crossing pattern of the fibres, but light and transparent at the same time (Fig. 2.15). The outlined design and fabrication methods were developed and tested through the construction. The machine covers a square area of 40 m2, encompasses a volume of ca. 125 m3 with the longest span of 8.4 metres and the maximum height of 4 metres (Thomson et al. 2015).
Fig. 2.15
The programming of it allowed a concurrent application of 9 epoxy resin infused carbon fibres with a speed of 0.01 m/s (ibid). The load path adjusted the placement of the fibrous material and the outcome of the fabrication strategy is visible in the final architectural prototype. The structural system is seamlessly connected to the design intentions as well as the performative criteria, which is innovative in the digital fabrication. The future research could potentially investigate how the multi-layering can work alongside the conventional building technology and services like heating and lighting. If the strategy is to be employed on a larger scale, the fabrication method should be adjusted to integrate numerous robots that are capable of delivering higher quantities of material to larger distances (ibid).
The reason why I chose this project as part of the precedent study is that it not only managed to design a functional shelter on a small scale but has also considered and proposed the fabrication on a larger scale. Additionally, the use of primary, secondary and tertiary structures, in this case, is different and reversed compared to the Silk Pavilion. The secondary structure namely the ETFE membrane was placed first and then, the primary structure was built underneath for the membrane to rest on it.
Fig. 2.14 14
The one aspect that unites all of these projects is the fact that the drive behind the design process was the naturally occurring weaving: spiders weave their webs and nests out of silk, just as silkworms weave their cocoons. It is safe to say that implementing a weaving strategy from insects on an architectural scale can result in highly resilient structures that are also relatively light. There are, however, evident challenges occurring due to the capabilities of software and scaling, but just by carefully analysing the insects’ strategy and adapting it to the basic architectural standards can result in not just an aesthetically pleasing, but a structurally innovative design.
Another uniting element other than the fibrebased approach is the use of technology: all of the precedents have incorporated digital media like Grasshopper algorithms and CNC machines, which has been appropriate and evidently beneficial. However, I am more interested in ways in which Attacus Atlas’s behaviour can be imitated utilising human’s craftsmanship skills rather than relying heavily on robots. Atlas moths are the builders of their own shelters; hence, I am trying to come up with an adaptation that humans can build themselves without the help of machines and sophisticated software because most of us do not have an access to such an advanced technology. There is no doubt that throughout the journey, working with the CAD software will take place in one way or another, but it will only slightly assist during the implementation process.
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C H A P T E R
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A T T A C U S
The Atlas Moth (Fig. 3.1) originally comes from South-East Asia and belongs to the Saturnidae family, which comprises the largest and some of the most appealing moths that can even rival some butterflies in their beauty (Kirby, W. 1892). Their larvae are relatively “social�, and feed on tree leaves such as citrus, mango, apple, cherry, cinnamon, the Tree of Heaven or privet (keepinginsects.com 2018). Atlas Moths have the largest wingspans amongst any Lepidoptera species, which can reach 29 centimetres (H. Clark. 1926).
A T L A S
Attacus Atlas require specific conditions to thrive. For example, since they are used to tropical climatic conditions, the temperature at which they can develop and pupate should ideally be around 25-30 degrees while humidity levels should be from 75% to 80%.
Even though their wings are mostly brown coloured, they feature quite astonishing patterns that comprise of snake-looking tips on their wings, which are presumably used for the protection against predators and four triangular windows that are a lot more translucent than the rest of their wings surfaces. Mating in Attacus Atlas happens quite quickly after pupation with female moths laying around 200-300 eggs that take approximately 12 to 14 days to hatch. They usually are no more than five millimetres in length and have black bodies covered in furry light yellow spikes. It is common for the caterpillars to not start feeding on leaves right after hatching, but normally they eat in large quantities and very often.
Fig. 3.1
It takes around 35 to 45 days for the caterpillars to grow and eat enough to be ready for pupation, which usually happens when the caterpillars reach 115 millimetres in length and become light green in colour with soft spines on their back. The pupa develops into a moth in 21 days and once emerged, the moth lives from 5 to 7 days due to the absence of mouth leaving them unable to eat (keepinginsects.com 2018).
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Over the summer, I decided that breeding Attacus Atlas myself would make it easier for me to gather the required information, as well as to witness the whole process of pupation in detail. I ordered 17 eggs (Fig. 3.2) online, which arrived on 26th of July 2017 in a sealed plastic tube which helped to prevent the eggs from damage. I bought clear plastic containers, placed a tissue at the bottom and made holes in them for ventilation. According to my plan, I needed to replace the containers with larger acrylic tanks once the pupae became too large.
However, to my disappointment, the first caterpillar died after living for just one day. I tried to observe the container and realized that the leaves were left untouched and the rest of the eggs have not hatched yet. I contacted the supplier and was advised to remove the tissue paper from the bottom of the container as well as increasing the temperature. Additionally, I was told to not have holes in the container, to wash leaves before feeding and keep the caterpillars away from the sun. In order to back up the citrus leaves, I have placed more green leafs of other species inside the container.
Fig. 3.2
Fig. 3.3
As a food source, I got a citrus (lemon) tree from a local nursery and when the deadline for the eggs to hatch has approached, I have placed a few fresh leaves at the bottom of the container. After 12 days since the dispatch, there was only one caterpillar (Fig. 3.3) that hatched and it started worrying me that it has not started feeding on leaves straight after hatching, but after doing some research, I realised that it was a common behaviour (see p.17).
On the morning of the 14th day, 6 more caterpillars hatched and seemed to have had good amounts of energy, but unfortunately, they also died without eating any of the fresh and washed leaves alongside those that hatched later in the day. It remains unknown to me why the caterpillars were not feeding on leaves, even though I made sure that the leaves came from the appropriate food source. After all of the larvae were dead, the breeding had to be terminated.
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Even though the failure was unexpected and frustrating, it has opened the eyes to several reasons why the personal attempt at rearing the pupae was rather ambitious. First, breeding larvae would take up significant amounts of time due to the number of days required for different stages of the moths’ lives, significantly slowing down the whole progress of the dissertation. Secondly, it would require very strict environmental conditions I would not be able to provide due to the seasonal changes and the overall local climate. Additionally, maintaining larvae by replacing tanks with bigger ones and supplying them with fresh leaves would result in high expenditures.
Having created the base, the caterpillar starts attaching it to the top of the leaf and then weaving a canopy while leaving a void in the middle and the sides. When the initial structural base is created, the caterpillar continues filling the voids sporadically weaving silk in a more gentle way. The density of the fibres at the start of the spinning process is a bit larger compared to the density of the fibres that are used to weave in between the structural framework of the cocoon. The last step is an additional reinforcement across the whole area of the cocoon from the inside.
Overall, undertaking such a long and expensive process to witness only two days of pupation seemed irrational and unrealistic. That made me turn to the research and data that was already available as well as jump straight to my point of interest, which was cocoons.
The final cocoon is prolonged and somewhat spindleshaped being more slender at the top of the leaf. It is light brown in colour with the rough granular outer surface (Fig. 3.6) and a smoother silky interior (Gosse, 2012). Its structure is very light, but protective and is capable of providing some light and ventilation within the minuscule pores that are left. The cocoons (Fig. 3.7) on average weight 10 grams, while their length and width are 4.4 cm and 1.9 cm respectively (R. P. Kavane, T. V. Sathe. 2014). However, female species tend to have slightly larger cocoons (ibid).
A cocoon for the Atlas Moth caterpillar is a refuge to undergo a metamorphosis; hence, it has to satisfy the following requirements: • Allowing ventilation to happen. • Allowing some natural light through the semitranslucent woven skin. • Protecting from biotic and abiotic environments. To observe the cocoon-spinning process I have done some research on video-graphic data and came across a time-lapse video (Butterfly World, 2016) (Fig. 3.4) which allowed me to observe the process (Fig. 3.5). A caterpillar usually finds a suspended leaf from a branch as a structural base to weave around and then starts its silk journey with a bottom-up approach. The caterpillar begins weaving a base for the cocoon at the bottom of the leaf, which serves as a basket for the caterpillar to go up and down while continuing to spin the cocoon.
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The described above phased construction results in the cocoons consisting of three specific layers. The exterior layer (Fig. 3.8) is not firmly secured and has a thickness of 0.5 mm and is responsible for 23 % of the combined weight of the cocoon (Reddy, N. et al. 2012). On the other hand, the intermediate layer (Fig. 3.9) is usually 0.6 mm thick forming the main part of the cocoons and accounts for 43 % of the total weight. The intermediate layer contains the majority of silk fibers and is loosely attached to the external layer, but firmly connected to the internal one. The rest 34% of the total cocoon weight is the internal layer (Fig. 3.10) that is on average 0.2 mm thick (ibid).
Fig. 3.4
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Fig. 3.5
Based on the images (Fig. 3.11 a, b, c, d), it is clear that the fibres of the external layer are loosely woven, while the other layers have a denser structure, with the internal layer having the least amount of space left between fibres.
Additionally, the caterpillar uses its biological adhesive to attach the fibres to each other in the internal and intermediate layers, whilst the external layer has almost no adhesive to hold the fibres together firmly. The fibres of the internal layer are also smaller in diameter with the average being 17 lm, while the external and intermediate layers fibres measured 19 lm and 20 lm each (ibid).
The layers also tend to decrease in their size with the internal one being the smallest.
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Fig. 3.8
Fig. 3.6
Fig. 3.9
Fig. 3.7
Fig. 3.10 22
Fig. 3.11 a
Fig. 3.11 b
Fig. 3.11 c
Fig. 3.11 d 23
C H A P T E R
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A P P L I C A T I O N
What I am planning to do in this chapter is to apply the described previously behaviour in architectural design, so I will start first by attempting to model the cocoon in 3D by using a CAD software. The axonometric (Fig. 4.1) is showing the threedimensional model of the cocoon exploded into three of its layers: exterior, intermediate and interior. The aim was to model the layers in the way that reflects the fibre density by making the exterior layer the least dense and the interior layer the densest. Because my focus in this part of the exploration was rather on the densities, the vertices do not reflect the exact woven patterns of the original cocoons.
I N
A R C H I T E C T U R E
Additionally, modelling such complex ornaments would have been extremely challenging. The modelling process started by building one cocoon and then duplicating it two times; hence, the intermediate layer was created first, while the rest were modelled afterwards with the properties of their surfaces changed. In order to achieve a difference in density, the amount of vertices has been altered with the external layer having very few compared to the rest. The model on the right comprises all of the layers in one cocoon resulting in a very dense, yet light structure. The layers were also altered slightly before creating one whole cocoon in order to reflect the size difference of each layer.
Fig. 4.1 25
Overall, the modelling process has helped to visualise The other way to interpret it is to see the intermediate the volume of each individual layer as well as of the layer as a primary structure with the secondary being whole cocoon. the internal layer while the exterior layer is tertiary. This can be related to a steel frame construction with What I see as a unique feature in the behaviour of the block infill where the steel beams serve as a primary Attacus Atlas compared to, as mentioned in Chapter structure with the block work being the secondary 1, a Bombyx mori or an Argyroneta aquatic, is a very and the battens for the exterior cladding - tertiary. sophisticated structural hierarchy. We could look at (Fig. 4.3) the leaf, for example, as a structural foundation for the cocoon, but it gets a bit tricky when we get to the However, if we go back to the leaf (Fig. 4.4) as a cocoon itself. structural foundation for the cocoon and look at it in its true state we will discover that it is, in fact, a very flexible base.
Fig. 4.2
Fig. 4.3
The chrysalis’s external layer can be interpreted as a primary structure, which the rest of the layers are added to just like a typical cold flat roof construction in timber frame where the joists are the primary structure with the timber deck and roofing resting on top of them (Fig. 4.2).
This refers back to the concept of resilience (Fig. 4.5) because the leaf can return to its original state if being deformed (Fig. 4.6 a, b, c, d); hence, how can we see it not as just a leaf by itself, but as an integrated structural framework within it that imitates the cocoon’s properties? How can we explore this concept of a flexible and resilient cocoon and implement it on an architectural scale?
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In order to test it out, a 1:50 card model has been created where the base is a very bendy piece of 1 mm card that represents the leaf with the primary, secondary and tertiary woven layers on top of it. The three layers of card (Fig. 4.7 a, b, c) represent the three stages of the cocoon with the varying densities and thicknesses. The external layer is a 200 gsm paper cut into thicker pieces with larger gaps left in the middle.
The intermediate and internal layers are made of 160 gsm and 120 gsm paper respectively with the internal layer featuring the thinnest strips that are densely interwoven. The external layer is the layer that, in this case needed the most adhesive because larger gaps required a more permanent fixation, while smaller gaps needed less because of a strength achieved through interweaving; hence, the interior layer required the least amount of adhesive, while with Attacus Atlas the amounts of adhesive needed were vice versa.
Fig. 4.4
Fig. 4.5 27
This is an example where the biological behaviour cannot be fully translated in an architectural scale; hence, requiring an alteration.
The resulting structure (Fig. 4.9 a, b, c, d, e) is very flexible and, even though is scaled down and made with card and paper, is quite resilient because of the strength achieved through the interwoven fibres of different thicknesses and densities.
Then, the three layers were glued to each other with adhesive yet again, which represents the biological protein glue (Fig. 4.8).
The resilience has been tested by challenging the model by bending and deforming it, which did not have any negative impact on it further reinforcing the claim (Fig. 4.10 a, b, c, d, e).
Fig. 4.6 a
Fig. 4.6 c
Fig. 4.6 b
Fig. 4.6 d 28
Fig. 4.7 a
Fig. 4.7 b
Fig. 4.9 a
Fig. 4.9 b 29
Fig. 4.7 c
Fig. 4.8
Fig. 4.9 c
Fig. 4.9 d 30
Fig. 4.9 e 31
Fig. 4.10 a 32
Fig. 4.10 b 33
Fig. 4.10 c 34
Fig. 4.10 d 35
Fig. 4.10 e 36
The outcome is aesthetically pleasing with the fibres acting as light filters during the day and as a public piece of lighting art during the night.
Another option could be using an inflatable membrane supported by the air pressure just like in the ICD/ITKE Research Pavilion, but due to the structure ideally to be built by humans and not robots, this strategy could be questionable.
Even though the model does not represent the cocoon visually in its true sense, it has applied and tested the similar structural approach. As was described in the introduction, a biomimetic approach is not necessarily about a full visual resemblance between the prototype and the predecessor, but about an awareness of certain challenges that might require alterations.
The other challenge, as was mentioned before is to find the appropriate building materials for the shelter that are indeed flexible, but resilient. In order to understand this challenge on an architectural scale, an investigation on a biological scale needs to be undertaken; hence, I turned to the exploration of the material properties of the Attacus Atlas silk including its tensile and mechanical behaviour.
For example, the foundation on a larger scale might require the most attention and thinking because if the aim is to resemble the cocoon visually alongside its structural hierarchy, the foundation has to behave in the same way as a leaf. This means it would have to be tensioned by the primary, secondary and tertiary elements; hence, it would have to be made out of a material that is very flexible, yet durable. The same rule, indeed, applies to the rest of the structure, but for the foundation, the material would have to be whole rather than fibrous. In addition, the flexibility of the material would have to be distributed in the way that allows a certain part of it to be flat for the purpose of stability and walkability if being used as a pavilion. The additional challenge would be to, just as the Attacus Atlas, start building the structure from the outside by reinforcing it from the inside with an intermediate and internal layer. In order to accomplish this, the first ‘loose’ external layer would have to be supported from the bottom with temporary columns or scaffolding that can subsequently be removed as the intermediate and internal layers were built (just as in the Silk Pavilion).
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C H A P T E R
4 :
M A T E R I A L P R O P E R T I E S A . A T L A S S I L K
Because Attacus Atlas’s cocoons contain an adhesive protein to hold the fibres together, a process named degumming has to take place in order to get rid of the protein by boiling cocoons in hot water. An experiment by (Poza, P. et al. 2002) has explored the stress and strain of the fibres by allowing them to dry for approximately 12 hours outside after degumming. Then, it was discovered that, even though the figures were estimations due to the complexity of the cocoon structures, the Attacus Atlas fibres (Fig. 5.1 a, b) were indeed unique and different compared to the fibres of the discussed earlier Bombyx Mori. The latter’s fibres have proven to be the strongest and least ductile, while the former’s elastic modulus was almost three times less (Fig. 5.2) (ibid).
O F
“The low-magnification aspect of one A. atlas fiber after tensile testing is shown in [Fig. 5.3]. The fiber was divided into several filaments near the failure region, and the fracture surface of one of the filaments is shown at higher magnification in [Fig. 5.4]. This micrograph shows that the filaments were, in turn, made up of microfibrils of 1 lm in diameter embedded in a soft matrix. They were pulled out from the matrix during fracture and the appearance of the end of one microfibril projecting from the fracture surface is presented in [Fig. 5.5].” (ibid)
Fig. 5.1 a
Fig. 5.2
Fig. 5.1 b 39
Based on this visual data, it is possible to identify a flexible microstructure that consists of individual fibres held together by an adhesive protein, which played a significant role in the mechanical behaviour. The reason behind the low elastic modulus is due to the high volume fraction of the tissue, which affects the rigidity of fibres. Additionally, another cause of the failure might be due to the withdrawal mechanisms of the fracture surfaces that are common for the organisms possessing a non-linear behaviour (ibid). The intriguing aspect of the discovery is the similarity between the fibrous matrix of Attacus Atlas and the man-made fibrous compounds.
However, even though the elastic modulus of Attacus Atlas fibres is lower than that of the Bombyx mori, its silk fibres are, in fact, coarser and especially those of the exterior layer, while the fibres within the internal layer are the finest (Reddy, N. et al. 2012). In addition, the cell density of the Attacus Atlas silk fibres is almost 80% higher than those of Bombyx Mori suggesting that Attacus Atlas fibres are prone to a fast recovery and cell production (ibid). The two other silkworms that were investigated were A. Mylitta and P. Ricini and it was discovered that their fibres were less refined with the latter’s elastic modulus being lower than that of Attacus Atlas (Fig. 5.6). The moisture regain in the silk fibres of Attacus Atlas is also higher compared to the other types of silks (ibid).
Fig. 5.3
Fig. 5.4
Fig. 5.7
Additionally, Attacus Atlas’s silk fibres have relatively unique tensile properties because of a distinctive architecture of their fibres. The silk of Attacus Atlas mostly contains glycine and only 18% of alanine with the presence of serine (Rigueiro et al. 2000). It has been reported that the Elastic modulus of the fibres would drastically decrease (Fig. 5.9 a, b) after encountering water (ibid). This is due to a negative impact water has on the adhesive protein within the silk fibres (Fig. 5.10 a, b) (Kakati LN, Chutia BC. 2009). Fig. 5.5 40
The Attacus Atlas fibres’ configuration of amino acids has also been proven to differ from those of Bombyx mori even though their mechanical properties are very much alike. The spider silk, on the other hand, has quite similar amino acid configuration to Attacus Atlas, while their mechanical properties are remarkably contrasting (Poza, P. et al. 2002).
The external layer has proven to have the highest stress to strain ratio with the intermediate layer possessing the lowest ratio amongst all three layers. What I find fascinating is the behaviour of silk when submerged in liquid media because various types of liquids can have different effects on the Young’s modulus of the fibres.
Based on the experiments above it is safe to say that Attacus Atlas indeed have unique silk fibres with high densities, cell growth and, compared to some other silkworms of Saturnidae family, tensile strength.
Fig. 5.9 a
Fig. 5.9 b
Fig. 5.10 a
Fig. 5.10 b 41
The fact that water has a negative impact on the modulus is something to consider whilst implementing the behaviour on an architectural scale because if it is a shelter, it has to be weather-resistant including being waterproof if proposed in a temperate maritime climate. As mentioned above, the reason behind the loss in tensile strength is due to the protein adhesive being weakened meaning that on a larger scale, similarly to the ICD/ITKE pavilion, a waterproof adhesive needs to be used, but due to the focus of this dissertation on a flexible structural performance, the amounts of adhesive needed might be considerably small.
If we compare the silk performance to other conventional architectural materials like steel, it is unlikely to perform similarly to the Attacus Atlas silk fibres due to a very high Young’s Modulus of steel. Bamboo and thin layers of wood, on the other hand, can potentially be possible solutions for the construction as they were in The Cocoon by AA Design & Make (Fig. 5.11) and in the Bug Dome by WEAK! Architects (Fig. 5.12).
Fig. 5.11
Fig. 5.12
What is worth noting is, even though the fibres lose their strength when being exposed to water, their cells possess unique qualities by being able to restore and grow efficiently. However, because silk is an insectproduced media, its performance and production may be heavily influenced by the diet or the conditions the Attacus Atlas is reared in.
The former has been built out of milled sheets of plywood and a Redwood Cedar tree to create a skeleton with flexible thin milled pieces of timber being added as a secondary structure (Frearson, 2013). The team’s intention was to utilise the natural materials available at the Hooke’s Park where The Cocoon was eventually placed hanging between three trees (ibid). Even though the project was not inspired by insect behaviour with it being named “The Cocoon” as a metaphor, it shows that timber can be a very suitable material to achieve undulating forms through weaving. 42
The latter has also been built using the locally available materials such as bamboo and diluted concrete acting as a cement. However, the project was actually inspired by insect shelters, unlike The Cocoon. The stiff bamboo ribs were bent to form the arches with thinner pieces of bamboo being threaded in between (Naidoo, R. 2009). The shelter served as a performance space for The 2009 Hong Kong & Shenzhen Biennale, but then became a gathering venue for illegal workers from the countryside (Coutard et al. 2016).
Based on these precedents, it is safe to suggest that bamboo or thin strips of wood could be suitable for the main structure as they are bendy, natural and are capable of forming very light, but strong constructions. Another advantage of those materials over, mentioned previously, carbon fibres is that they are easy to work with for humans without the need to use sophisticated 3D printing machines or CNC robots. They are also more accessible and environmentally friendly. It is also worth noting that bamboo, in particular, has many similarities with Attacus Atlas fibres because both have their tensile strength challenged when submerged in water due to it having a negative impact on the adhesive within fibres (Chen et al. 2015).
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C O N C L U S I O N To conclude, we have explored the early forms of construction utilised by humans and compared them to those of larval insects. Pointing out the advantages of the latter, we have established an argument on why the insects and, Attacus Atlas, in particular, can act as architects to learn from due to the efficiency and resilience of their structures achieved via the complex application of fibres.
After learning about the properties of the material on a biological scale, we came up with the proposition of the material on an architectural scale reinforcing the argument with two additional case studies. The aim of this study was to prove that a biomimetic fibre-based approach in architecture can result in very resilient structures that are also functional and aesthetically pleasing.
In order to reinforce the argument, we turned to the exploration of two case studies that have applied the biomimetic fibre-based approach covering their subjects of interest, manufacturing processes and findings. The research helped us to understand how certain challenges can be tackled on an architectural scale.
Attacus Atlas was chosen to reinforce the argument and, based on all the discoveries and research in this study, it was a great “architect” to learn from. However, in order to fully examine and test their use in architecture, much more work needs to be done. This could involve an observation of cocoon weaving processes of several moths as was done in ICD/ ITKE Pavilion, a utilisation of a more sophisticated CAD software and, if necessary, the use of robots in the construction alongside humans. Additionally, a further investigation could be done regarding the materials potentially experimenting and altering the existing ones.
Then, we switched to our main protagonist namely Attacus Atlas covering the background information, an unsuccessful rearing experiment as well as the analysis of their shelter’s structure and building strategy. The research led to certain discoveries including the structural hierarchy of cocoons as well as the fibre densities of each layer. Based on the findings from the previous two chapters, a personal practical experiment was pursued which covered the exploration of volumes of cocoon’s layers and the resilience of the cocoon’s foundation (leaf). A 1:50 prototype has been created that utilised the cocoon’s structural hierarchy and the fibrous components. The prototype reflected the knowledge obtained from the case studies regarding a potential manufacturing process, but in order to have a stronger proposition regarding the materiality, the research took a turn towards the material properties of the insect’s fibres.
All of the above would require a high budget, access to very advanced technology, a large time-frame and a team of very skilled people. The topic of a fibre-based design is relatively new and, due to the efforts of practitioners such as Neri Oxman, is making its way into the industry. Oxman believes that learning from larval insects can lead to building very efficient structures by utilising 3D printers in collaboration with CNC robots. “In traditional 3D printing, the gantry-size poses an obvious limitation; it is defined by three axes and typically requires the use of support material, both of which are limiting for the designer who wishes to print in larger scales and achieve structural and material complexity. Once we place a 3D printing head on a robotic arm, we free up these limitations almost instantly.” - stated Oxman.
The exploration led to a better understanding of the fibres regarding their tensile and mechanical behaviour. It was discovered that the protagonist’s fibres are unique amongst other larval insects as well as within its own construction with each layer possessing fibres of different qualities. 45
I highly support Oxman in her argument regarding learning from nature to propose structures that are resilient and relatively light. The benefits of such approach are multiple including the outcomes being structurally stable without the need for internal supports, visually appealing features as well as an efficient use of materials. Additionally, 3D printers and CNC robots themselves have many advantages to humans due to their incredible accuracy and speed. However, I do believe that it is important to not let the robots gain an upper hand in manufacturing due to their tendency to, as any other technical device, fail. In order to deliver a successful biomimetic project, a balanced integration of both humans and robots is required with the latter being responsible for only the manufacturing process. “Many people think that, with computers, you just press a button and the computer does it, which is, of course, totally idiotic.� (Zaha Hadid 2013) Overall, biomimicry is a highly beneficial practice, especially if learning from larval insects such as Attacus Atlas because of the efficient use of a material as well as a clever employment of structural hierarchy producing very resilient structures. Even though the advantages of such particular approach have been explored to a limited extent, I do believe that it has a very high potential to positively impact on the way we, as architects, think and design. This, in return, can allow us to shape better spaces, buildings and cities in the future. Much effort will be made to continue the research regarding the topic of this dissertation in order to further reinforce the argument and to, potentially, come up with a 1:1 prototype.
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L I S T
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I L L U S T R A T I O N S
Front Cover: Image by Author
Fig. 2.10: Image by Roland Halbe
Fig. 1.1 a, b: Images by author
Fig. 2.11: Courtesy of ICD/ITKE University Stuttgart
Fig. 1.2: Image by author
Fig. 2.12: Courtesy of ICD/ITKE University Stuttgart
Fig. 1.3: Image by Ingo Arndt
Fig. 2.13: Courtesy of ICD/ITKE University Stuttgart
Fig. 1.4: Image by author
Fig. 2.14: Courtesy of ICD/ITKE University Stuttgart
Fig. 1.5: Image by author
Fig. 2.15: Courtesy of ICD/ITKE University Stuttgart
Fig. 2.1: Image by Markus Kayser
Fig. 3.1: Image by author
Fig. 2.2: Image by Carlos David Gonzales Uribe
Fig. 3.2: Image by author
Fig. 2.3: Image by Carlos David Gonzales Uribe
Fig. 3.3: Image by author
Fig. 2.4: Schematics of the human-constructed portion of the pavilion, by Jorge Duro-Royo
Fig. 3.4: Courtesy of Butterfly World Fig. 3.5: Image by author
Fig. 2.5: Schematics of the human-constructed portion of the pavilion, by Jorge Duro-Royo
Fig. 3.6: Image by author
Fig. 2.6: Courtesy of MIT Media Lab
Fig. 3.7: Courtesy of Journal of Polymers and the Environment
Fig. 2.7: Image by Markus Kayser
Fig. 3.8: Courtesy of Journal of Polymers and the Environment
Fig. 2.8: Image by Steven Keating Fig. 2.9: Image by Roland Halbe
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Fig. 3.9: Courtesy of Journal of Polymers and the Environment
Fig. 5.3: Courtesy of Engineering Fracture Mechanics
Fig. 3.10: Courtesy of Journal of Polymers and the Environment
Fig. 5.4: Courtesy of Engineering Fracture Mechanics
Fig. 3.11 a, b, c, d: Images by author
Fig. 5.5: Courtesy of Engineering Fracture Mechanics
Fig. 4.1: Image by author
Fig. 5.6: Courtesy of Journal of Polymers and the Environment
Fig. 4.2: Image by author Fig. 4.3: Image by author
Fig. 5.7: Courtesy of Journal of Polymers and the Environment
Fig. 4.4: Image by author
Fig. 5.8: Courtesy of Journal of Polymers and the Environment
Fig. 4.5: Image by author Fig. 4.6 a, b, c, d: Images by author
Fig. 5.9 a, b: Courtesy of Journal of Applied Polymer Science
Fig. 4.7 a, b, c: Images by author Fig. 4.8: Image by author
Fig. 5.10 a, b: Courtesy of Journal of Applied Polymer Science
Fig. 4.9 a, b, c, d, e: Images by author
Fig. 5.11: Image by Hugo G. Urrutia
Fig. 4.10 a, b, c, d, e: Images by author
Fig. 5.12: Courtesy of WEAK!
Fig. 5.1 a, b: Courtesy of Journal of Polymers and the Environment
Back Cover: Image by Author
Fig. 5.2: Courtesy of Engineering Fracture Mechanics
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Thank you