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