AA School of Architecture | Emergent Technologies and Design | Biomimetics Workshop Meta-Joint

Natural Systems & Biomimetics

META-JOINT Joint System Bio-Inspried from Tortoise Shell

Architectural Association Emergent Technologies and Design 2014-2015

Sulaiman Alothman Yu Tao Song Patrick Andrew Tanhuanco

META|JOINT Alothman, Song, Tanhuanco

CONTENTS V

Abstract

VI

Introduction Chapter 1 | Tortoise Shell

8

1.1 Tortoise Shell

9

1.2 Shell Anatomy

10

1.3 Stress Distribution

11

1.4 Scutes Growth Direction

12

1.5 Suture Chapter 2 | Abstraction and Analysis

14

2.1 Abstraction from Biology

16

2.2 Identified Parameters

18

2.3 Methods and Material

19

2.4 Experiments

22

2.5 Evaluation Chapter 3 | System Development

24

3.1 System Parameters

26

3.2 Joint | connector

28

3.3 Physical Test

30

3.4 Digital Test

32

3.5 Prolifiration

33

3.6 Form Optimization Chapter 4 | Further Advancement

34

4.1 Other Types of Joint System

36

4.2 Joint Surface

38

4.3 Feedback Mechanism for Joint Surface

40

4.4 AA EmTech Core Studio 1 Project

41

4.5 Material Selection

42

Conclusion

44

Bibliography

META | JOINT

Abstract

The Tortoise shell, characteristic of its bulging geometry, is widely known to serve as a

Acknowledgment of the developed relation-

protection for the animal. The shell itself is

ship enabled the team to improve local joint

a complex system composed of multi-layers

system of the previously identified parameters,

and joinery systems of skeletal elements and

allowing different local actions within the joint

membranes that function collectively when

system; such as, and rotation, locking and out-

subjected to external loads- such as predator

of-plane directionality. This experiment chal-

attacks, falling on rocks or when moving. One

lenges the function of the joint not just a mere

of the most significant layers is the suture – the

connector of two separate elements, but also a

area where bones interlock and grow. This ele-

component itself to develop a global geometry

ment is also responsible for the flexibility of the

with specific performance and function.

shell, allowing it to lock and become stiff when subjected to high compression loads and allow small deformations under small loads. This flexibility is the principle the team abstracted for this Biomimetics research. Experiments were carried out by investigating and testing identi-

V

fied parameters on physical and digital models to understand the relationship between the resulting design, its performance and the limit for its different overall geometries.

META | JOINT

INTRODUCTION

Michael Pawlyn stated in his talk at the

geometry, outer layer (scutes), etc. The length

Disruptive Innovation Festival 2014 held last

of the suture - a zigzag-like connection, the

November 12, that we as human beings are

width of the suture, the angle of the teeth,

“enchanted with our technology and think that

etc., are investigated and abstracted. These

our technology is better than nature… “, then

principles and parameters are carried out

adding that “we have a new humility now”, as

primarily through experimenting with physical

we step back and realize that nature already

models supported by digital domain. These

has the solutions. “We’ve moved from trying to

are discussed in Chapter 2 – “Abstraction

dominate nature, to trying to protect bits of it,

and Analysis” where the team first tried to

to learning from it.1”

understand what parameters are involved, how the geometry is affected, and its resulting

Learning from nature is the objective of this

performance.

Biomimetics and Natural Systems research -

VI

by exploring different natural systems and be

In the third Chapter – “System Development”,

able to identify design principles that can be

the team takes their understanding based on

abstracted and utilized to design and develop

the abstraction and analysis carried in chapter

an innovative system.

2, and inquires how this can be developed further into an innovative joint system. In this

The team focused on the Tortoise shell with

stage, a feedback loop is established, and a

its characteristic novel jointing of parts and

back-and-forth investigation on the finalized

its variable stiffness performance when

parameters is performed. The local joint, and

functioning as a whole system, as a shell.

component-based system emerges from the

Research based on a number of scientific

defined parameters. The adjustment of the

resources helped the team to understand how

parameter affect the global geometry, its

the Tortoise shell and its composition perform

performance, and its limits in scalability.

especially when subjected to external forces.

These findings are discussed in the first Chapter – “Biology: Tortoise Shell”.

The team then moved on to abstract the principles learned from the tortoise shell with a particular focus on the suture - the connection between the dermal bone layerand investigated both structural and design performances specific to the suture with the aim to obtain an understanding of its relationships to various elements such as shell’s

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

This led the team to learn and raise questions

in itself? These questions helped further drive

of which are discussed in Chapter 4 - Further

the experiment and open the possibilities of the

developments on why certain geometries

design and development of a jointing system

fail, which geometries are more efficient for

resulting in a specific behavior with different

specific performance targets, what limitations

performance from local, regional, to global

are imposed by the material of choice. Is there

system.

an ‘intelligent’ way to design a joint without resulting into mechanical parts? Should a joint be limited to only act as a connector to different components, or can it be a component

[biology inspiration]

[abstraction]

[speculation]

ABOVE Design process diagram

VII

1 Disruptive Innovation Festival live webcast aired last November 12, 2014, from 6:00-7:00pm; Michael Pawlyn & Janine Benyus on Biomimicry (http://thinkdif.co/)

META | JOINT

Tortoise Shell

1.1 TORTOISE SHELL

The Tortoise or Turtle shell is a complex

layer is composed of bones and ribs joined by

composite of layers that function collectively to

the vertebral spine.

produce more efficient mechanical properties compared to its individual parts. The turtle shell

The growth pattern of the scutes, which is

has continued to evolve with its unchanged

the first defensive layer, and the joining of the

compositions and geometry for more than 200

bones with the suture provide the shell with

million years.

higher stiffness and strength to withstand compression and high strain loads.

Therefore,

Archai & Wagner (2013) states that the shell is

the research will investigate the overall stress

a hierarchical composite armor is attached to

flow on the turtle shell, types of growth pattern

its body and designed to protect it from trauma

of the scutes, and the sutures.

caused by sharp and blunt impact loads such

8

as predator assaults, smashing against rocks, or

According to Hu, Saliert and Gordon (2011),

falling.1 Not only does the shell provide physical

the understanding of the complex material

protection, but also function as a reservoir

properties is a limitation in predicting the

for water, fat, or wastes. The turtle shell is

strength of natural shells.2 For the purpose

composed of two major parts, the upper part,

of this study, the focus will be more on the

the carapace connected to the lower part, the

understanding of the mechanism of the specific

plastron, via lateral bridges. The carapace

layer of interest - the suture, and its abstraction

consists of outer and inner layer. The outer layer

and application to an architectural system.

is called scutes, a keratinous layer, and the inner

[Carapace]

[Lateral Bridges]

[Plastron]

FIG.1.1.1 Turtle | photo: Cole Jeffries, flickr.com

1 Achrai, B., & Wagner, D. H. (2013). Micro-structure and mechanical properties of the turtle carapace as a biological composite shield. Acta Biomaterialia 9, p. 5890 2 Hu, D. L., Sielert, K., & Gordon, M. (Nov-December 2011). Turtle Shell and Mammal Skull Resistance to Fracture Due to Predator Bites and Ground Impact. Journal of Mechanics of Materials and Structures, p.1197

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

1.2 SHELL ANATOMY

Sulci (connection between scutes)

Scutes (Keratein protection layer)

Bones organization

Ribs 9

Sutures (connection between bones)

Top shell

Bottom shell

Plastron

FIG.1.2.1 Turtle | photo: Cole Jeffries, flickr.com Turtle shell anatomy’s diagram

CHAPTER | 1 TORTOISE SHELL

1.3 STRESS DISTRIBUTION

It is also important to consider the implications

sutures act as an important part to distribute

of the geometry of the shell (shape &

the force and allow the shell to absorb shock,

curvature) to its load bearing performance,

deformation, and become rigid at very high

since various morphologies of shells exist

force.

depending on specie type and its environment.

For the purpose of this Biomimetics research,

In the study of Zhang, Wu, Zhang, & Chen

we limit our scope to understand how the

(2012), they concluded that there are four ribs

arrangement and geometry of the bones

connecting the shell top board and bottom

affects in distributing the compressive

plate. “Under a compressive load, the ribs will

stresses only. Magwene & Socha (2012) has

be subjected to compression, and thus the four

conducted whole shell testing on a number

ribs look like four pillars to help support the

of turtles but they note that “it is difficult to

top board. However, the shell as a whole will

accurately estimate the stresses bore by the

be subjected to bending load so that the inside

shells in either situation due to the complicated

surface is under tension while the outmost

geometry of the shell and the dynamically

surface is under compression. [...] There is a

changing area ”.3

bio-fiber reinforced composite film,[...] and it is believed that the distribution of these bio-

10 Once the forces are applied on the vertebra

fiberes from the rib, inside and bottom surface

of the turtle shell, most of the force will flow

of the shell follow the stress direction to resist

along the spanning direction of the bones. The

cracking”. They will investigate on this further.4

FIG.1.3.1 Stress flow on turtle shell | plan view

FIG.1.3.2 Stress flow on outer and inner layer of the carapace | axon

3 Magwene, P. M., & Socha, J. J. (2012). Biomechanics of Turtle Shells: How Whole Shells Fail in Compression. Journal of Experimental Zoology 9999A, p.7.

4 Zhang, W., Wu, C., Zhang, C., & Chen, Z. (2012). Microstructure and mechanical property of turtle shell. Theoretical & Applied Mechanics Letters 2, 014009 p.4.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

1.4 SCUTES GROWTH DIRECTION

Another interesting feature of the Tortoise shell

as a possiblity for the proliferation of the

is the growth and proliferation of the scutes.

joint by introducing nodes of connection and

The scutes which are keratinous and exible,

allowing the system grow in multiple directions

are the visible epidermal plates that cover the

or planes.

plate-like bones and may be thick or paperthin. As the tortoise hatchling grows, the outlines of the scutes are preserved as small nodes either at the center or at the side of each scute. As it grows, keratin proliferates around its periphery as well as the entire underside of the scute5, and these produce the visible lines or growth rings. The team deems this principle

11

FIG.1.4.1 Scutes growth from edge | image: Bels, Godfrey, Wyneken. 2007. Biology of Turtles.

FIG.1.4.2 Scutes growth from center | image: Bels, Godfrey, Wyneken. 2007. Biology of Turtles.

5 Pritchard, P. C. (2008). Chapter 3 Evolution and Structure of the Turtle Shell. In J. Wyneken, M. H. Godfrey, & V. Bels, Biology of Turtles (pp. 46-82). Boca Raton, FL: CRC Press. p.53

CHAPTER | 1 TORTOISE SHELL

1.5 SUTURE

The inner layer of the turtle shell is mainly a

in the center is important for swimming and

bony layer designed to protect the shell from

buoyancy.

external loads, and therefore, it needs to be

12

stiff. However, flexibility is required when

According to Krauss, Zelzer, Fratzl, and Shahar,

performing various actions, such as respiration

“ The interdigitated nature of the structure

or locomotion. It is found that the soft joint

of the sutures allows them to move relatively

between the bones, the suture, can allow

freely towards each other under small loads.

some degree of deformation under minor

However, once a critical threshold deformation

loads, and can become rigid and stiff when

is reached, the opposing ends of adjoining

subjected to heavy loads, such as predator

dermal bones meet, and the shell becomes a

attacks. The forming of the shell inaugurates

much more rigid structure 7”. The behavior

in the embryonic stage with the formation

of the bones under external loads and the

of the ribs and the vertebrae, and then, the

degree of deformation are dependent on a

bones start to form right after hatching.6

number of paramters, such as the length of

The dermal bones are interconnected with a

the sutures, the number of teeth in the suture,

zigzag-like connection, the suture, allowing

the suture width, the angle of interdigitation,

for further growth of the shell . The flat bone

etc. Therefore, Our design intent is to develop

structure consists of two thin sheets of bone

theses parameters in an architectural and

which are dense on the sides and porous on

structural systems to allow locking between the

the center; this differentiation provides high

parts, but flexibility of the whole.

bending-stiffness, and the porosity and voids

Scutes

Suture Ribs covering the bones Suture

FIG.1.5.1 Diagram of dermal bone layer in carapace | axon

6 Krauss, S., Monsonego-Ornan, E., Zelzer, E., Fratzl, P., & Shahar, R. (2009). Mechanical Function of a Complex Three-Dimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider Turtle. Advanced Materials, 21(4), p. 407 7

Ibid., 410.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

3 Compression

Force (KN)

2

Point

1

0 0

5

10

Deformation (mm)

200 Bone

Suture

FIG.1.5.2 Diagram of mechanical function of the suture. a) unloaded beam. b) loaded beam. c) detail of locking teeth | Krauss, Zelzer, Fratzl, and Shahar.

Stress (MPa)

100

0 0.0

0.1

0.2

Strain

FIG.1.5.3 Graph. a) whole shell subject to compression and point loading. b) stress and strain trace of bone and suture tissue sample | Hu, Sielert, &Gordon.

FIG.1.5.4 Microscopic image showing the ribs and bones in the center the suture on bothe sides | Krauss, Zelzer, Fratzl, and Shahar.

CHAPTER | 1 TORTOISE SHELL

13

Abstraction and Analysis

2.1 ABSTRACTION FROM BIOLOGY

Based on the understanding of how the biology

out to test these relationships first. Once

of the Tortoise shell performs the team then

thorough understanding of the local system is

abstracted principles and prepared objectives to

achieved, component aggregation, arrangement

help drive the research forward. By looking into

and potential for a deployable structure may

three scales of the tortoise shell, the team was

or would function as a feedback mechanism in

able to identify principles relating to its local

further developing and optimizing the design of

parts particularly in the sutures as an adaptive

the joint.

joint that functions accordingly depending on

14

the type of load imposed on it; on a regional

The team identifies the study to be hierarchical

level – the positioning of scutes, flatbones and

by trying to understand the local levels which

ribs as the geometrical arrangement responsible

are the governing parameters that would

for the shell’s growth and load distribution; and

affect the geometric design of the joint, its

on a global level, the final arrangement of all

mathematical relationship which are the

the bones, and how these contribute to the load

dimensions of the geometry and resulting

distribution and overall shell growth.

angles of rotation, and finally have an understanding of the limitations from material

With these principles in mind, potential

of choice.

investigation focus was identified by means of setting objectives and hypothesizing on possible outcomes set at the table FIG.2.1.1. On the local scale, the team thought of developing a joint system that allows flexibility and a locking mechanism fixing the joint at a desired angle.

It is important to understand how parameters relate to the geometry outcome and its resulting behavior, therefore experiments were carried

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

Parts of Tortoise Shell

Investigation Focus

Principles Abstracted

Joint Flexibility and Locking Mechanism

Local

Sutures

Regional

Position of Scutes, Flatbones, Ribs

Global

Adaptive Bone Joints

Whole shell structure based on arragement of parts

• •

Flexible under small loads Rigid under heavy loads

• • •

Component Aggregation/Arrangement

Geometrical Arrangement •

bone growth

• •

Geometric Constraints •

Optimum, or allowable bending angles Other parameters involved Joint design efficiency vs. bone sutures

Application for other possible geometries Possibility of scaling by adding components

Deployable Structure

how whole shell responds to distriute loads; and parts assembled to keep the global geometry

• •

Compression by desired geometry Compression by Curvature

Hierarchical > Geometric > Mathematic > Material FIG. 2.1.1 Table showing summary of principles that can be abstracted from the intitial research about the tortoise shell potential investigation focus.

Goals for Investigation To investigate and develop a joint that: • has freedom of movement up to a specified angle • can fix into one or more angles of rotation • can lock into a rigid position once the required angle is reached

FIG. 2.1.2 Diagrams showing the team’s initial goals for investigation, and hypothesis of possible joint configurations to achieve the set goals.

CHAPTER 2 | ABSTRACTION AND ANALYSIS

15

2.2 PARAMETERS IDENTIFIED

Based on the team’s research findings about the

design of the tortoise shell’s sutures. This is

Tortoise shell and their succeeding experiments,

used as a precedent to explore the identified

they conclude that the geometry of the joint

parameters and how it can provide a solution to

is one of the most fundamental driver of the

the investigation focus.

system as it affects the relationship of one element and how this interacts with another,

Width (w) – the width pertains to the spacing

thus affecting the performance of the joint.

between the two members, allowing for

The geometry is governed by four general

movement of the joint, even when the pin is

parameters the Width, Distance, Depth and

fully inside the socket. As the two members

Angle (at joint shoulder).

increase their distance from one another, the width is increased.

Also based on the study done by Lin et.al (2014) they concluded that a triangular shape

Distance (L)– this parameter is governed by the

is the most optimal geometry “allowing for

length of the pin and the depth of the socket.

high stiffness, toughness, and high integrity due to its ability to uniformly distribute stress” 16

and this is why this geometry is evident in the

How far the pin is from inside the socket helps 1

determine the degree of angle of roation the joint is cabale of achieving. The deeper the pin

(a) Width

Distance (L) Geometry

Depth

Performance Freedom of movement; Rotation of joint

Angle (ѳ)

1 Lin, E., Li, Y., Ortiz, C., & Boyce, M. C. (2014). 3D printed, bio-inspired prototypes and analytical models for structured suture interfaces with geometrically-tuned deformation and failure behavior. Journal of the Mechanics and Physics of Solids 73, p.180-181

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

is in the socket, the less rotation; the farther it is

the joint cannot slide out or separate from one

from inside, the more rotation.

another. The sum of the angles of both shoulders of the socket and pin informs the angle of

Depth (D) - Depth is determined by the

rotation.

geometric design of the joint. The team explored a triangular, round geometry for the pins.

Having identified these parameters, the team proceeded to test and adjust them. Also the team

Angle at Shoulder (ѳ) – The angle of the shoulder

tries different geometries to compare which

also helps determine the amount of movement

of them are efficient in achieving the set goals

and rotation of the joint. This parameter is

outlined in Fig. 2.1.2.

important especially when the two elements of

(b)

17 (c)

The spacing (w) and angle at joint shoulder allows minimum movement of joint while fully in the socket.

Depth (D) which is the geometry of the joint allows for the amount of sliding that can be accomodated by the joint which results in the distance (L) of the pin from the end of the socket, thereby increasing the width (w) allowing for more freedom of movement and angle and rotation. The angle at the shoulder here becomes negligible.

(d)

FIG. 2.2.1 (a) Chart of relationships of parameters, geometry and performance; (b) Parameters identified in a basic geometry abstracted from tortoise shell; (c) Interelationship of parameters and results (d) Phyiscal model showing the parametric relationships

CHAPTER 2 | ABSTRACTION AND ANALYSIS

2.3 METHODS AND MATERIALS

The abstraction and investigation of the

at the latter stages of the development. For

principles is based primarily on building

the abstraction and analysis part of the study,

physical models to test the relationship of

the team focused on trying to first develop a

parameters, geometry and performance.

geometry that can help achieve the objectives

Sections of the test geometries were first

of controlling the angle of rotation and locking

designed in a CAD interface, then laser-cut

after reaching the desired angle. All initial

on 3mm MDF, and finally using the layering

experiments were done in a 25mm section

technique to glue assemble the cut pieces.

(1in.) height, then scaled down to test the limits

MDF was used for this experiment mainly for

of the material and geometry with the smallest

the advantage of fabrication in economy and

working size at a 10mm section.

time for testing experiements, the limitations faced by the team by this choice of material is discussed in Chapter 4 section 4.5 “Material Selection”.

Digital parametric modeling was also utilized 18

FIG. 2.3.1 Layering of MDF Sheets allows the possiblity of a thick section for experiments, opening possiblities for the joint not just to function as a connector, but a component itself as well.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

2.4 EXPERIMENTS

A number of tests were made by varying the

along the socket. The farther the groove from

parameters, resulting in different geometries

inside, a higher angle of rotation is achieved.

and performance. Among these tests, 3 types of geometry are established as showin in

[2a] – the circular joint section is an attempt to

Fig.2.4.1 -a triangular shaped joint section

try to address what if the joints are attached

[1a], a circular shaped section [2a], and a

together in the first place, and how the

curvilinear type [3a]; These three provide good

geometry can control the angle of rotation in a

rotational movements, and are tested further to

specific locking position. The ‘ball-and-socket

investigate the possibility of the joint locking at

joint’ served as a precedent to this joint type.

a specific angle.

However a ball and socket joint has almost 360 degrees of rotational freedom. Joint [2a] takes

For [1a], the section of the joint is manipulated

advantage of the geometry by the depth of the

to include grooves at the socket. As the pin

circular geometry, and the angle at the joint

slides out, its ‘hammer-shaped’ head slides into

shoulders.

the groove therefore achieving a specific angle of rotation. The groove can then be moved 19

[1a]

[2a]

[3a]

FIG. 2.4.1 Select geometries of the initial experiments: 1a - Triangular shaped joint section; 2a - Circular joint section; 3a - Cuvilinear joint section

CHAPTER 2 | ABSTRACTION AND ANALYSIS

2.4 EXPERIMENTS

[3a] – is an improvement of [1a], wherein

discussed in a study by Krauss et. al (2009),

the rigid angles of the triangular geometry is

when they did experiements in a micro scale

curved to better control the sliding of the pin in

and showed that the fiber orientations within

and out of the socket.

the sutures are arranged in a way that fibers are

All these three types require manual

loaded in tension when the shell is loaded in

manipulation for sliding the joints and in the

compression.2

desired angle and direction. However, these

Without the internal locking mechanism

joints do not retain the specified angle, even

present in Strategy 1, the joints will not stay

when left standing; it collapses by its own

in its desired angle position unless a tension

weight. The team then considered how they

element is added at the opposite side to keep

can control both the angle and locking. Two

the pin pressed against the groove or socket

strategies were introduced and investigated.

in compression. (This strategy is investigated

The first strategy was manipulating the

further in Chapter 3 system development)

geometry of the joint, therefore introducing an internal locking mechanism within the joint (see Fig. 2.4.2). There are some limitations 20

to the first strategy. For example, all three experiments are limited to only rotation and locking in one direction instead of two (without locking mechanism). [2b] is non-reversible after locking and [1b] can only have one specific angle of locking. [3b] shows more promise as it can at most have two angles of locking position.

This second locking strategy (Fig. 2.4.3) takes into principle how the tortoise shell becomes rigid when subjected to heavy loads, allowing the sutures to come into compression. This is

2 Krauss, S., Monsonego-Ornan, E., Zelzer, E., Fratzl, P., & Shahar, R. (2009). Mechanical Function of a Complex ThreeDimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider Turtle. Advanced Materials, 21(4), p. 409

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

Locking Strategies

[1b]

[2b]

21

[3b]

FIG. 2.4.2 Locking Strategy 1 By manipulating the geometry of the joint notches and stoppers are introduced producing an internal locking mechanism This type of joint design allows the joint to rotate and fix at a specified angle.

FIG. 2.4.3 Locking Strategy 2 Compression of the sutures in the turtle shell allow it to be rigid at heavy loads. without the internal locking mechanism similar present in Strategy 1, the joints have to be held in compression to retain its fixed angle position, thus the need to introduce a tension element.

This tension element may be applied by using elastic materials such as rubber bands, or a stretchable fabric membrane.

CHAPTER 2 | ABSTRACTION AND ANALYSIS

2.5 EVALUATION

The experiments are summarized in the analysis

that the ‘optimum’ joint design and angle

table (Fig. 2-8). All joint sections are made by

cannot be identified until feedback from the

laser cut on 3mm MDF, with 5 sheets layered,

component level and global geometry informs

and a section height of 25mm. These joints are

of the constraints for further adjustments and

investigated with objectives to achieve freedom

modifications to its local geometry.

of movement up to a specified angle, ability

Based on this evaluation, the joint [3b] meets

to fix into one or more angles of rotation, and

the objectives as stated earlier and for the

the ability to lock into a rigid position once

purpose of this study, this joint type will be

required angle is reached.

developed for the next phase. However, this

These objectives are translated into four criteria

does not mean that the other types are entirely

namely, the limits of the angle of rotation,

discarded, as these types also provided the

ability to lock and support its own weight,

team with different possibilities for further

reversibility after locking, scalability where the

development, and they may be used as

minimum height of the section is determined.

precedents for other joint developments

The joints are evaluated according to these

depending on a set criteria.

criteria and the test that meets most of the 22

objectives will be further developed in the system development phase.

Creating diffent joint types allowed the team to determine possibilities and limitations of different parameter changes that result in developing joint’s geometry. Joints that have built-in locking mechanism are not reversible ([1b],[2b],[3b]), and joints without locking mechanisms in turn need to have an external tensioning element to lock the joints in compression. The team also realizes

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

[3b]

[3a]

[2b]

[2a]

[1b]

[1a]

Laser-cut on 3mm MDF 5 layers Section height 25mm

Physical Test Models

Pre-determined 10° ,15°

0 to15°

Yes

Yes

No No

Yes

16.3°

Pre-determined

Yes

Pre-determined

0 to 45°

No No

Yes

Pre-determined; but allows for free movement

Yes

11°

No No

Locking and SelfLoad Support

Pre-determined

Pre-determined 0,11° to 23°

Generally all angles are pre-determined by the geometry design of the joint. The goal is to identify the angle optimum for the desired global geometry

Angle of Rotation (limits)

23

FIG. 2.5.1 Analysis Table, Select Joints from initial experiments

CHAPTER 2 | ABSTRACTION AND ANALYSIS

Reversability

h = min. 20mm

h = min. 10mm

h = min. 10mm

Yes

No

h = min. 10mm

h = min. 15mm

h = min. 10mm

Scalability

No

Yes

No

Yes

Performance of the joint to return to its original position after rotation and/or locking

h

Curves longer pin allows for better control in sliding and locking

Slide and lock; No Rotation

Curves and a longer pin allows for better control in sliding

Free Rotation, Slides out easily

Keeps the joint in place; Stopper locks joint at specific angle and prevents rotation after.

Keeps the joint in place; Allows for rotation until joint shoulders reach compression.

Keeps joint in place; Locks only in single position; Stopper may lose rigidity after being subject to load for long periods (mechanical property of material)

has free rotation but joint slides out easily; Angles are pre-determined by set grooves

Geometric Consequences

System Development

3.1 SYSTEM PARAMETERS

The analysis and evaluation of the abstracted

4. the radius of the front tip and the back tips.

joints from the tortoise shell research conducted in chapter 2 - “Abstraction and

The second category is specific to the

Analysis”, has led the team to define a series

neighboring joint relating to the rotation

of parameters to provide differentiation in

angle for the locking mechanism. Also, the

the geometry and stiffness to the joint. In

angle between the front and tail is a proposal

the tortoise shell, the suture performance and

that could be adopted in later stage of joint

stiffness depends on a number of variables

development.

such as: the number and length of the teeth, the angle between the teeth, the geometry of the teeth, etc., which “allow the shell some extra degree of flexibility under load.” 1 Similarly, our defined parameters for the joint 24

system will have this degree of flexibility to achieve the required stiffness for an intended geometry. The joint experienced a series of physical testing and digital analysis to reach a level of optimization for different geometries.

The joint has developed parametrically with our defined parameters as inputs for the process, which are divided into two categories. The first one is specific to the joint itself (Fig. 3.1.1a), and includes the following: 1. distance between the outer and inner tips.

2. the width of the joint.

3. the length of the joint.

1 Krauss, S., Monsonego-Ornan, E., Zelzer, E., Fratzl, P., & Shahar, R. (2009). Mechanical Function of a Complex Three-Dimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider Turtle. Advanced Materials, 21(4), p. 410

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

ius

ad er

us adi r p i

sid

width

h

lengt

t ips een t w t e nce b dista

25

y-transilation

[a]

egree ion d t a t o r

[b]

ion nsilat x-tra

tail ip/ t w l b/

e

ang

[c]

FIG.3.1.1 Diagram of system parameters | axon

CHAPTER 3 | SYSTEM DEVELOPMENT

3.2 JOINT | CONNECTOR

The digital modification of our defined

have the possibility to take the form of a

parameters results in an emergence of different

triangle proliferating in three sides or can be an

geometries with specific performance and

octagon proliferating from eight sides. These

criteria. It is in fact what we want to achieve

criteria are determined by the spanning of

from the proposed joint system, a joint or a

the parts and also the global geometry of the

connection acts as an individual local system

system (Fig.3.2.1b).

providing different positions for locking and attaching to other individual parts. These

The understanding of the logic of the parts and

individual local parts are attached to a

connectors assembly led to an initial regional

'connector' piece. The connector allows for

system with opportunities for proliferation and

changing directionality and stiffness of the

levels for differentiation (fig. 3.2.2). A tension

whole system.

membrane (rubber band) is proposed to secure the locking of the parts into the connector

26

Depending on the required stiffness and rigidity

element. This is a departure point towards a

of the joint system, the individual parts are

more complex geometry for our

subjected to geometrical form manipulation

development process.

in accordance (Fig.3.2.1a). An individual part can only become male joint on both sides or can have male joint on one side and and female-joint on the other depending on the stiffness required. Similarly, the connectors

[a]

[b]

FIG.3.2.1 (a) variation of parts/joints. (b) variation of connectors

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

deformation

27

angles variation

10 20

FIG.3.2.2 Logic of assembly diagram | axon

CHAPTER 3 | SYSTEM DEVELOPMENT

3.3 PHYSICAL TEST

The development of the joint system requires

(Fig.3.3.2a/b). In fact, this structural failure

a series of physical testing in regards to

could be utilized to also change the Y and

structural failure. One of the observation is

X-direction of the individual part, as not only

evident at both tips of the tail of an individual

being limited to the Z-direction, allowing more

part. Under tension imposed by the rubber

possibilities for the overall geometries.

band, the top tip fails due to the small area of material allocation and also due to the material properties of MDF, leading to the bottom tip to fail as well (Fig.3.3.1a/b).

Another observation lies on the individual part going out of its original plane laterally. This is caused by the tension force exceeding the resistance capabilities of the surface area of the individual part (thickness/number of layers) 28

[c]

[a]

[b]

FIG.3.3.1 (a) high stresses on top tip imposed by tension; leading to failure. (b) resulted failure. (c) lateral moment.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

29 [a]

[b]

FIG.3.3.2 (a).(b) lateral moment as a result of lack of insufficient joint thickness and small locking surface area.

CHAPTER 3 | SYSTEM DEVELOPMENT

3.4 DIGITAL TEST

Structural Analysis is performed for form

another type of material that is good in both

optimization and efficiency of the individual

tension and compression will minimize such

parts or joints. These were run in conjunction

failure.

with the physical testing conducted in earlier experimentation. The ďŹ rst structural analysis

The second structural analysis is related to the

examines the displacement of the individual

individual joint under vertical loads. Similar to

part in relationship to its neighboring parts.

the physical testing result, the behavior under

Local buckling results from the stress imposed

such load is mainly caused by lateral moment

by the locking action of other connecting part,

deviating the joint from its original plane. One

however, it is not as critical as the high stresses

of the solution to overcome such failure is to

taking place at the tips of tail of the individual

round the tip and the surface area receiving it.

part. By increasing material at these highstress areas, increasing the thickness (number of layers composing the joint), or utilizing

30

[Utilization]

[Displacement]

[Utilization]

[Displacement]

FIG.3.4.1 Structural analysis using Karamba3d for utilization and displacement under applied loads towards form optimization.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

[Utilization]

[Displacement]

31

[Utilization]

[Displacement]

[Utilization]

[Displacement]

FIG.3.4.2 Structural analysis using Karamba3d for utilization and displacement under applied loads towards form optimization.

CHAPTER 3 | SYSTEM DEVELOPMENT

3.5 PROLIFERATION

The proliferation process inaugurates with

however, we can easily replace an individual

the assembly of the individual joints to the

part within the whole system if necessary.

connector element. Once they are assembled, the tension (rubber band) is introduced. Then,

During the assembly process, we encountered

each individual joint is pulled and locked to the

the issue of the joint moving laterally out of its

desired angle, in which the tension will secure it

plane causing the whole system to collapse.

in place (Fig.3.5.1).

Part of the problem was resolved when increasing the number of layers (thickness) to

The geometry of the system is dependent

the joint itself.

primarily on the locking angle, in which we can only control during the fabrication process,

32

FIG.3.5.1 Regional assembly from 00 to 150 angle

FIG.3.5.2 Global assembly of two regional-scale components

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

3.6 FORM OPTIMIZATION

Based on the digital analysis done on the individual-joint form with applied loads, and the physical testing of these joints on a regional system, the team were informed how to optimize the form of the joint. By adding more layers, thus, increasing the joint's thickness, and therefore reducing the lateral movement when locking under tension.

Furthermore, the width of the joint was increased in the middle, and this allowed more stability and stiffness, providing more surface area at the tips for locking.

33

FIG.3.6.1 The evolution of form for the individual joint towards optimization

FIG.3.6.3 Optimized regional-scale model

CHAPTER 3 | SYSTEM DEVELOPMENT

Further Advancements 4.1 OTHER TYPES OF JOINT SYSTEM

During the system development stage, two

developments raise these questions, should

possibilities of joint solutions were investigated

the system incorporate mechanical means

for the purpose of addressing issues relating

of connection, or a would developing an

to the initial study of linear proliferation of the

interlocking mechanism within the components

joint and its potential to be a deployable and

be a smarter solution?

packing system.

For the purpose of this study the team selected

The joint system at Fig.4.1.1 shows how a

to develop the joint system by introducing a

change in the overall geometry of the body –

connector with interlocking components. The

i.e. changing the angle can result in a different

other two developments are not discarded, as

form, in this case a curved form when parts are

these provide potential solutions depending

attached together. The resulting performance

on the performance criteria set, in which the

is a joint that can extend and contract, thus

team believes these systems can be developed

opening the potential for a deployable system.

further in another study.

Parts are proliferated by attaching them to 34

‘nodes’, and a global geometry is formed.

The second joint system at Fig.4.1.2 is a development that seeks to address the linear proliferation by allowing the joint to rotate in different direction at specified segments of the components. It also incorporates a sliding mechanism allowing the joint to lock in compression when a tension element is introduced, and changing its form again when the tension is released. However, both joint

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

FIG. 4.1.1 Joint system allowing rotation, potential packing and deployability

35

vs.

Mechanical

FIG. 4.1.2 Joint system allowing change in direction of plane

Interlocking

FIG. 4.1.1 Potential joint developments either by mechanical means of connection or purely geometric interface by interlocking materials and components.

CHAPTER 4 | FURTHER ADVANCEMENTS

4.2 JOINT SURFACE

Our investigation and development for the

a degree of scalability for the components,

suture-inspired joint system limits itself to a

providing stiffness to areas where they are

linear approach towards forming a 3D skeleton

subjected to higher stress levels.

geometry. In this stage, a transition to a surface integrated joint is promoted to enable new functions. The Joints are sandwiched between two layers of wood material forming the component. A tension member made of wood veneer is utilized to secure the connection between two components (Fig.4.3.1). The triangular geometry promotes

36 2nd layer of wood veneer 1st layer of wood veneer connection support

tip connection

tip’s housing cover layer

FIG. 4.3.1 Component assembly | axon

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

FIG. 4.3.2 Compenents’ prolifiration | axon, plan view

37

FIG. 4.3.3 Physical model | MDF FIG. 4.3.4 Angle variations of the individual joint

CHAPTER 4 | FURTHER ADVANCEMENTS

4.3 FEEDBACK MECHANISM FOR JOINT SURFACE

The team learned that a feedback mechanism

creating openings (Fig.4.3.6).

has to be established to facilitate the development of the joint geometry. A bottom-

This investigation is performed with a triangular

up or top-down approach, or a balance of

geometry as a component surface; however,

both can be utilized depending on a set

the exercise is not limited to such. Further

criteria. A top-down approach looks into the

advancements can be taken by testing different

regional level of connections and the possible

geometries, volumes, and allowing these

global geometry, which inform the limitations

investigations to inform the development of

in performance of a specific joint design.

joints that are capable of achieving specific

The design of the joint can be re-configured

types of connections and movements.

otherwise or exhaust all possibilities with a joint designin which the local relationships will govern the resulting regional and global geometry. Images on the right illustrate the possible outcomes depending on how the joint can perform: Fig. 4.3.5 shows that the 38

joint needs to be capable of opening up a gap between elements to generate a global curved surface. While a different type of form is achieved when the joints are restricted in

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

[a]

[b]

Fig 4.3.5 [a] Method 1. Changing angle with corresponding distance | axon. [b] Possible global geometry resulted from method 1.

39

[a]

[b]

Fig 4.3.6 [a] Method 2. Changing angle with ball joints | axon. [b] Possible global geometry resulted from method 2.

CHAPTER 4 | FURTHER ADVANCEMENTS

4.4 AA EMTECH CORE STUDIO 1 PROJECT

One of the further advancements of this study

geometry, lock its position, and then assembled

is the incorporation of a joint system in one

with other components. Hence, the team took

of the AA EmTech Core Studio 1 Projects.

into consideration the principles investigated

The project takes as precedent the folding

in this joint system study to develop a joint

technique in designing a system for urban

that will help keep the folded components in

intervention at the Masthouse Terrace Pier,

compression, guide the geometry from a at

Isle of Dogs, London. Their aim was to have a

sheet to its desired folding angle and lock, and

system which can be used as a self-supporting

to connect it to other components to assemble

structure but also be exible enough to

the whole structure.

accommodate the movements caused by the wind and displacements of the platform due to the tidal changes. Due to the limits of fabrication in their study, the proposed structure at the site cannot be designed in a single sheet. The solution was to fabricate components that will fold to achieve its desired 40

Joint Exploration

Legend - Least desired / Least Viable for project

The joint component was introduced into the development of the system for the following reasons: Control the freedom of movement of components; allow the system to fold and lock at specific angles; also connect different components at regional level;

Joint Performance

Selected Joints Explored Type 1

- Most desired / Most Viable for project

Freedom of Rotation Amount of rotation the joint allows for flexibility and movement of the component parts once joint is placed

None (fixed) Fixed Geometry

Flat sheet components will be rigid after joints are screwed in.

Locking

Reversability

Facilitates components to retain their folded state/angles

Ability of joint to return to its original flat state without removing or dismantling parts

Controlled by geometry of triangular lock pieces Tendency for system to be too rigid, thus carries more stress in components

Fabrication and Installation How the joint is applied to the system

After components are folded, attached piece by piece and screwed/riveted in.

Needs to be unscrewed piece by piece

Joint is responsible for locking the components in a specific angle/ advantageous for packing and storage

Flat sheet components are easily returned to its original unpacked state by simple action of pulling.

Grooves are built on sheet components. Extensive geometry manipulation required

None

Type 2

Compression Groove Joint

Depending on stength of compression provided by pre-stressed membrane

Without constant compression - has tendency to slip out or move out of plane Controlled by depth of groove, thickness of material, & pre-stressed membrane

Type 3

Slide-Rotate-Lock

Two directions depending on geometry of joint. But sometimes it becomes difficult to control

Locking depends on geometry of joint, distance of slide and rotation. Needs prestressed member to keep joint locked in compression and specific angle

Components return to original state by pulling the jointsto release compression, though it is often difficult to control the movement

Joints as pre-fabricated component; Attached with or after assembly of components; may face challenges in packing and storage

Components return to original state by pulling the joints to release teeth in groove; then joints are removed.

Joints as pre-fabricated component; Attached after assembly of components on sides requiring direction of folding

Type 4

Rotate - Lock

One Direction only.

Once locked, still allows for minimal movement to absorb impact loads and allowing minimal displacement

Once teeth are inserted to the grooves, provides a strong locking mechanism

FIG. 4.2.1 Joint studies at AA EmTech Core Studio 1 Project by Chavan, Zhou, Mzily, Tanhuanco

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

4.5 MATERIAL SELECTION

The choice of Medum-Density Fiberboard

Its lack of flexibility due to its low modulus

(MDF) as material for the system development

of elasticity causes the material to break

is based on economy in fabrication, scale and

evident in the physical model tests of the

time, to efficiently create sections of joints

system development discussed in Chapter 3.

by laser-cutting and layering sheets to form

Developing the geometry of the joint is also

components for testing. However, the system

limited to only one axis of the plane. To create a

is not intended to be developed with MDF as

joint that has controlled freedom of movement

the final material of choice. By using MDF, the

in 2 or more planes, or creating a component

team realized that it also provided numerous

with joints along its sides using MDF will require

challenges and limitations as they were

more layering and assembly work. The team

developing the system.

recommends that further advancements in this

These limitations are by the material properties

research may be taken by testing materials that

of the MDF, which the sheet is designed

have flexible properties and test geometries by

to be rigid, thus affecting the potential

3D printing, or CNC milling.

performance of the system, especially when the joints are designed to bend and rotate.

41

FIG. 4.3.1 3D-printed socket for ball joint, developed in one of the AA EmTech Dissertations “Reconfigurable Mold for Double Curved Panels” by Fasai Al Barazi, Georgios Bitsianis, Stanley Carroll, Amro Kabbara

CHAPTER 4 | FURTHER ADVANCEMENTS

Conclusion

The tortoise shell is a good example of an

conduct their own experiments with a final aim

emergent system, whereby its individual parts

to develop an innovative system based on the

and layers such as the bones, the sutures,

abstracted principles. The team investigated

and scutes, with their own properties and

on developing a joint system that not only acts

functions, are organized into a geometry that

as a connection but also can function with

works collectively. They give the shell its unique

freedom of movement and locking into a rigid

mechanical properties to act as a whole system

position once a specific angle is reached.

enabling it to withstand and respond to various types of loads imposed on it. Focusing on the

Throughout a series of experiments, the team

individual parts, the team shed light on the

focused on developing and optimizing the

sutures because of its unique functions that

geometry of the joint.

cater to the shell structure.

42

The team learns in the research of Magawene

The geometry is collectively affected by four

and Socha (2012) that despite the sutures

parameters that the team identified. Modifying

having a lower bending strength compared

the geometry, the joints can either be restricted

to the bones surrounding it, they are able to

or have more freedom of movement.

absorb similar amounts of forces due to its greater strain values, giving the shell some

These findings are general and thus enabled

flexibility when subjected to smaller loads, and

the team to come-up with various joint types

rigidity at larger loads.1 Also, the suture is the

and many other possibilities. However, for the

site of bone growth and it plays an important

purpose of this research, there is a need to set

part in the whole development of the whole

specific criteria for which joint type to develop

shell as a protective measure for the turtle.

further. Thus, this investigation leads them to have a thorough understanding on how the

Based on the researched gathered, the team

parameters interact resulting in a geometry and

abstracted principles from how the parts of

degree of performance. They also realized that

the tortoise shell function and proceeded to

after having this understanding, a feedback

1 Magwene, P. M., & Socha, J. J. (2012). Biomechanics of Turtle Shells: How Whole Shells Fail in Compression.

Journal of Experimental Zoology 9999A, p.11

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

mechanism has to be established, which is the

There are many possibilities for this joint

assembly of the joint into a regional and global

system to be further developed as abstracting

system that will inform them how to improve

the principles from the Tortoise shell is not only

or develop the geometry of the joint further to

limited to a single or fixed solution. Therefore

accomplish a specific purpose.

the team identifiy their own parameters that result in a geometry with specific performance

As the team carried out the investigation

levels. The criteria for evaluation and the

from the abstraction up until the system

development includes, choice of materials,

development phase, they experienced the

the feedback mechanism of proliferation and

disadvantages using MDF as a material choice

scaling of the system and physical and digital

for the experiment as it limits the potential

testing, allows the unique development of the

of the system to perform better in rotation,

meta-joint.

in locking, and changing of angles due to its low modulus of elasticity. The material tends to break easily when subjected to high compression or tension forces. However the material is easy to work with in regards to

43

fabrication in economy and time.

Experiments with physical models informed the team about importance of material selection and scalability of the design, providing a good feedback on how the parameters interact in a 1:1 scale, thereby facilitating decisions and adjustments to the digital platform.

CHAPTER 4 | FURTHER ADVANCEMENTS

Bibliography

Achrai, B., & Wagner, D. H. (2013). Micro-structure and mechanical properties of the turtle carapace as a biological composite shield. Acta Biomaterialia 9, 5890-5902.

Archrai, B., Bar-On, B., & Wagner, D. H. (2014). Bending mechanics of the red-eared slider turtle carapace. Journal of the Mechanical Behavior of Biomedical Materials 30, 223-233.

Damiens, R., Rhee, H., Hwang, Y., Park, S., Hammi, Y., & Lim, H. (2012).

Compressive Behavior of a turtle’s shell: Experiement, modeling and simulation. Journal of the Mechanical Behavior of Biomedical Materials 6, 106-112.

Ed. Wyneken, J., Godfrey, M. H., & Bels, V. (2008). Biology of Turtles.

Boca Raton, FL: CRC Press.

Hu, D. L., Sielert, K., & Gordon, M. (Nov-December 2011). Turtle Shell and Mammal Skull Resistance to Fracture Due to Predator Bites and Ground Impact. Journal of Mechanics of Materials and Structures, 1197-1211.

Krauss, S., Monsonego-Ornan, E., Zelzer, E., Fratzl, P., & Shahar, R. (2009). Mechanical Function of a Complex Three-Dimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider Turtle.

Advanced Materials, 21(4), 407-412.

44

Lin, E., Li, Y., Ortiz, C., & Boyce, M. C. (2014). 3D printed, bio-inspired prototypes and analytical models for structured suture interfaces with geometrically-tuned deformation and failure behavior. Journal of the Mechanics and Physics of Solids 73, 166-182.

Magwene, P. M., & Socha, J. J. (2012). Biomechanics of Turtle Shells: How Whole Shells Fail in Compression. Journal of Experimental Zoology 9999A, 1-13.

Vega, C., & Stayton, T. C. (2011). Dimorphism in Shell Shape and Strenght in Two Species of Emydid Turtle. Herpetologica 67(4), 397405.

Zhang, W., Wu, C., Zhang, C., & Chen, Z. (2012). Microstructure and mechanical property of turtle shell. Theoretical & Applied Mechanics Letters 2, 014009 1-5.

TORTOISE SHELL | NATURAL SYSTEMS AND BIOMIMETICS, 2014

45

ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE GRADUATE SCHOOL PROGRAMMES COVERSHEET FOR SUBMISSION 2014-2015

PROGRAMME: Emergent Technologies & Design TERM: 1

STUDENT NAME(S): Sulaiman Alothman, Yu Tao Song, Patrick Tanhuanco SUBMISSION TITLE: Natural Systems and Biomimetics: Tortoise Shell

COURSE TITLE: Natural Systems and Biomimetics COURSE TUTORS: Michael Weinstock, George Jeronimidis, Evan Greenberg, Manja van de Worp, Mehran Gharleghi

SUBMISSION DATE: 01.12.2015

DECLARATION: “I certify that this piece of work is entirely our own and that any quotation or paraphrases from the published or unpublished work of others is duly acknowledged.”

Signature of Student(s):

Sulaiman Alothman Date: 01.12.2015

Yu Tao Song

Patrick Andrew Tanhuanco