Livro - Advanced Materials and Structures and their Fabrication Processes

Prévia do material em texto

Advanced Materials and Structures
and their Fabrication Processes
Book manuscript, Narvik University College, HiN
Dag Lukkassen and Annette Meidell
August 23, 2007
Contents
I Materials and Structures 8
1 Ceramics and glasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1 Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2 Glasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3 Industrial Importance of Ceramics and Glasses . . . . . . . . . . . 13
1.4 Industrially Important Glasses . . . . . . . . . . . . . . . . . . . . 14
1.5 Technical Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.1 High-performance ceramics . . . . . . . . . . . . . . . . . . 15
2 Metals and metal alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1 High-peformance Metals . . . . . . . . . . . . . . . . . . . . . . . 19
2.1.1 High-Performance Aluminum . . . . . . . . . . . . . . . . 19
2.1.2 High-Performance Steel . . . . . . . . . . . . . . . . . . . . 20
2.1.3 Space-age metals . . . . . . . . . . . . . . . . . . . . . . . 20
3 Polymers and Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1 The structure of polymers . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Crystallinity in polymers . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.1 The glass transition temperature and melting temperature 26
3.3 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Properties of plastics . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.1 Thermosettings . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4.2 Types of Thermosettings . . . . . . . . . . . . . . . . . . . 30
3.4.3 Thermoplastics . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4.4 Types of Thermoplastics . . . . . . . . . . . . . . . . . . . 34
3.5 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.6 Additives in Plastics . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.6.1 Oriented Plastics . . . . . . . . . . . . . . . . . . . . . . . 41
3.7 Elastomers & Rubbers . . . . . . . . . . . . . . . . . . . . . . . . 41
3.7.1 Rubber and Artificial Elastomers . . . . . . . . . . . . . . 43
3.8 Biopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.8.1 What makes a polymer a biopolymer? . . . . . . . . . . . 47
3.8.2 Applications of biopolymers . . . . . . . . . . . . . . . . . 48
3.8.3 Properties of biopolymers . . . . . . . . . . . . . . . . . . 48
3.8.4 Additional information on raw materials in biopolymers . . 50
3.8.5 Plastic taste better with sugar . . . . . . . . . . . . . . . . 51
4 Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.1 The history of composites . . . . . . . . . . . . . . . . . . . . . . 56
4.2 Natural composites . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3 Man-made Composites . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.1 Fiber-Reinforced Composites . . . . . . . . . . . . . . . . . 60
4.3.2 Classification of composites . . . . . . . . . . . . . . . . . 60
4.4 Ceramic matrix composites CMC . . . . . . . . . . . . . . . . . . 61
4.5 Metal Matrix Composites MMC . . . . . . . . . . . . . . . . . . . 64
4.6 Polymer Matrix Composites PMC . . . . . . . . . . . . . . . . . . 65
4.7 Fiber reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.7.1 Choosing fibers . . . . . . . . . . . . . . . . . . . . . . . . 67
4.7.2 Glass fibers . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.7.3 Carbon fibers . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.7.4 Boron fiber . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.7.5 Ceramic fibers . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.7.6 Polymer Fibers . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7.7 Carbon nanotube (CNT) fibers . . . . . . . . . . . . . . . 74
4.7.8 Fiber hybrids . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.7.9 Spider silk . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.8 Aerogel composites . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.9 Textile composites . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.10 Bio-inspired materials . . . . . . . . . . . . . . . . . . . . . . . . 78
4.11 Self-healing composites . . . . . . . . . . . . . . . . . . . . . . . . 79
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4.12 Left-handed metamaterials . . . . . . . . . . . . . . . . . . . . . . 81
5 Smart (intelligent) Materials and Structures . . . . . . . . . . . . . . . 87
5.1 Color Changing Materials . . . . . . . . . . . . . . . . . . . . . . 88
5.1.1 Photochromic materials . . . . . . . . . . . . . . . . . . . 88
5.1.2 Thermochromic materials . . . . . . . . . . . . . . . . . . 88
5.2 Light Emitting Materials . . . . . . . . . . . . . . . . . . . . . . . 88
5.2.1 Electroluminescent materials . . . . . . . . . . . . . . . . . 89
5.2.2 Fluorescent materials . . . . . . . . . . . . . . . . . . . . . 89
5.2.3 Phosphorescent materials . . . . . . . . . . . . . . . . . . . 90
5.3 Moving Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.3.1 Conducting polymers . . . . . . . . . . . . . . . . . . . . . 91
5.3.2 Dielectric elastomers . . . . . . . . . . . . . . . . . . . . . 92
5.3.3 Piezoelectric materials . . . . . . . . . . . . . . . . . . . . 92
5.3.4 Polymer gels . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.3.5 Shape memory materials (SMM) . . . . . . . . . . . . . . 94
5.3.6 Nanostructured Shape Memory Materials . . . . . . . . . . 95
5.3.7 Magnetic Shape Memory (MSM) Materials . . . . . . . . . 96
5.4 Temperature Changing Materials . . . . . . . . . . . . . . . . . . 97
5.4.1 Thermoelectric materials . . . . . . . . . . . . . . . . . . . 97
6 Functional Gradient Materials . . . . . . . . . . . . . . . . . . . . . . . 98
7 Solar Cell Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.1 Light-absorbing materials . . . . . . . . . . . . . . . . . . . . . . 101
7.2 Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.3 Thin films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.4 Silicon solar cell device manufacture . . . . . . . . . . . . . . . . . 104
8 Nano - materials - and technology . . . . . . . . . . . . . . . . . . . . . 106
8.1 Carbon Nanotubes (CNT) . . . . . . . . . . . . . . . . . . . . . . 107
8.1.1 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
8.2 Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8.3 Flexible ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
8.4 New type of High-performance Ceramic . . . . . . . . . . . . . . . 111
8.5 Back to square one? . . . . . . . . . . . . . . . . . . . . . . . . . 112
9 Cellular Solids, Structures & Foams . . . . . . . . . . . . . . . . . . . . 116
9.1 Metal Foams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
9.1.1 Aluminium foam: . . . . . . . . . . . . . . . . . . . . . . . 118
9.2 Polymeric foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
9.3 Refractory foams / Ceramic foam . . . . . . . . . . . . . . . . . . 122
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9.3.1 Carbon foam . . . . . . . . . . . . . . . . . . . . . . . . . 123
9.4 Hierarchical structures (multiscale structures) . . . . . . . . . . . 123
9.5 Biomaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
II Sandwich Constructions 127
10 Why use sandwich constructions? . . . . . . . . . . . . . . . . . . . . . 128
10.1 Face materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
10.2 Core materials and structures . . . . . . . . . . . . . . . . . . . . 131
10.2.1 Foam Cores . . . . . . . . . . . . . . . . . . . . . . . . . . 132
10.2.2 Honeycomb Cores . . . . . . . . . . . . . . . . . . . . . . . 13210.2.3 Corrugated Cores . . . . . . . . . . . . . . . . . . . . . . . 135
10.2.4 Wood Cores . . . . . . . . . . . . . . . . . . . . . . . . . . 136
10.3 Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
11 Design of sandwich constructions . . . . . . . . . . . . . . . . . . . . . 140
11.1 Design of sandwich beams . . . . . . . . . . . . . . . . . . . . . . 140
11.2 Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
11.3 The Flexural Rigidity and Shear Rigidity . . . . . . . . . . . . . . 143
11.4 Tensile and Compressive Stresses . . . . . . . . . . . . . . . . . . 144
11.4.1 Due to bending (transversal loading) . . . . . . . . . . . . 144
11.4.2 Due to in-plane loading (axial) . . . . . . . . . . . . . . . 147
11.5 Shear stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
11.5.1 Summary of approximations . . . . . . . . . . . . . . . . . 153
11.6 Sandwich design: stiffness, strength and weight . . . . . . . . . . 155
11.7 Example of beam calculations . . . . . . . . . . . . . . . . . . . . 157
11.8 Strength and stiffness design example . . . . . . . . . . . . . . . . 160
12 Failure modes of sandwich panel . . . . . . . . . . . . . . . . . . . . . . 163
12.1 Failure loads and stresses . . . . . . . . . . . . . . . . . . . . . . . 164
12.2 Failure-mode maps . . . . . . . . . . . . . . . . . . . . . . . . . . 167
12.2.1 Transition equation between face yielding and face wrinkling 167
12.2.2 Transition equation between face yield and core shear . . . 169
12.2.3 Transition equation between face wrinkling and core shear 169
13 Design Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
13.1 The stiffness of sandwich structures and its optimization . . . . . 174
13.1.1 Example of minimum weight design for given stiffness . . . 177
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III Cellular Solids 180
14 Some definitions of cellular solids . . . . . . . . . . . . . . . . . . . . . 180
14.1 Mechanics of honeycombs . . . . . . . . . . . . . . . . . . . . . . 183
14.2 In-plane deformation properties, uniaxial loading of hexagonal hon-
eycombs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
14.2.1 Linear-elastic deformation . . . . . . . . . . . . . . . . . . 184
14.3 Out-of-plane deformation properties . . . . . . . . . . . . . . . . . 187
14.3.1 Linear-elastic deformation . . . . . . . . . . . . . . . . . . 188
IV Mechanics and Effective Properties of Composite
Structures and Honeycombs 191
15 On effective Properties of Composite Structures . . . . . . . . . . . . . 191
16 The thermal problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
17 Isotropic elastic materials . . . . . . . . . . . . . . . . . . . . . . . . . . 193
18 Orthotropic composites . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
19 Square symmetric unidirectional two-phase structure . . . . . . . . . . 196
19.1 Calculation of stiffness and compliance matrix . . . . . . . . . . . 198
20 Numerical methods for periodic structures . . . . . . . . . . . . . . . . 200
20.1 Coordinate transformation . . . . . . . . . . . . . . . . . . . . . . 202
21 A computational example . . . . . . . . . . . . . . . . . . . . . . . . . 206
V Fabrication processes 210
22 Fabrication of plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
22.1 Processing of Rubber and elastomers . . . . . . . . . . . . . . . . 218
23 Fabrication of Fiber-Reinforced Composites (FRC) . . . . . . . . . . . 221
23.1 Manufacturing processes of Reinforcements . . . . . . . . . . . . 221
23.2 Prepregs, Preforms and Compounds . . . . . . . . . . . . . . . . . 223
23.3 Fabrication processes of FRC . . . . . . . . . . . . . . . . . . . . 224
23.4 Fabrication of Functionally Gradient Materials . . . . . . . . . . . 229
23.5 Fabrication of sandwich constructions . . . . . . . . . . . . . . . . 229
24 Layer Manufacturing Technology (LMT) . . . . . . . . . . . . . . . . . 233
24.1 Ballistic particle manufacturing (inkjet) BMP . . . . . . . . . . . 235
24.2 Fused deposition modelling - FDM . . . . . . . . . . . . . . . . . 235
24.3 LOM - Laminated object manufacturing . . . . . . . . . . . . . . 236
24.4 Selective laser sintering - SLS . . . . . . . . . . . . . . . . . . . . 236
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24.5 Laser Engineered Net Shaping (LENS) . . . . . . . . . . . . . . . 237
24.6 Stereo lithography - SLA . . . . . . . . . . . . . . . . . . . . . . . 238
24.7 Solid ground curing - SGC . . . . . . . . . . . . . . . . . . . . . . 239
24.8 Three dimensional printing (3DP) . . . . . . . . . . . . . . . . . . 240
24.9 PowderProcessing/PowderMetallurgy . . . . . . . . . . . . . . . . 241
24.10Vapor Deposition CVD/PVD . . . . . . . . . . . . . . . . . . . . 243
24.11Selection of a layered manufacturing process . . . . . . . . . . . . 243
25 Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
25.1 Designing for Manufacturability (DFM) ) . . . . . . . . . . . . . . 247
25.2 Product design guidelines . . . . . . . . . . . . . . . . . . . . . . 248
25.3 Evaluation of design alternatives . . . . . . . . . . . . . . . . . . . 249
25.4 The meaning of colors . . . . . . . . . . . . . . . . . . . . . . . . 250
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Preface
This manuscript is written in order to use it as lecture notes in the course ”Ad-
vanced materials” given at Narvik University College for master students in the
field of Engineering Design. In the course the students will be familiar with differ-
ent kind of advanced materials and structures such as for instance smart materials,
functional gradient materials, polymers and plastics, nano-materials, elastomers
and rubbers, biopolymers, cellular solids and structures, and different types of
composite materials, which can be found in Part 1 of this report. In Part 2, the
fabrication-processes of different advanced materials, structures and forms is de-
scribed. The different types of sandwich constructions included the design of such
structures are subjects that are discussed in Part 3, while in Part 4 we will have
a closer look at mechanics and effective properties of composite structures and
honeycombs.
This report may also be used as literature for students studying mechanical
engineering, material science, production engineering. We assume that the reader
has a bachelor degree in Engineering.
7
Figure 0.1: Classes of materials.
Part I
Materials and Structures
In this part we will mainly consider the concepts of materials and structures. The
difference between a material and a structure is not clearly defined. Many draw
the lines between what you understand as a homogeneous material when you see
it with your bare eyes, and the inhomogeneous material structure that you clearly
see is made up of a fixed geometry or mixing of materials. For instance an alloy is
by this definition a material even though it consists of two or more components,
but a honeycomb core built up of two different components is a structure.
Materials are often classified into the six broad classes that are shown in figure
0.1; metals, ceramics, glasses, elastomers, polymers and composites. But, when
we also include material structures, the number is bigger, and the classification
of the term ”materials and structures”, even though it is not a conventional way
of making a classification, may look like the one purposed in figure 0.2. We will
in this book briefly mention main properties of each group in figure 0.2, but the
advanced term in the title of the book refers to a thoroughly study of composites,
polymers, smart materials, sandwich constructions, nano-technology, functional
materials, cellular structures.
8
Figure 0.2: Classes of materials and structures.
High Performance Materials (HPM)
High-performance materials (or Advanced Engineering Materials) are materi-
als that provide specific performance advantages in comparisonwith the counter-
part conventional materials. Often it is difficult to place materials strictly into the
group of high-performance group or other groups, but we often divide materials
into the following main groups:
• Standard materials, which are used in products that is exposed to non-
critical environments and low-stress applications
• Standard Engineering Materials, which are used in products that must
have general bearing and wear properties
• High-performance materials or advanced engineering materials, which
are used in products that must have superior properties (extreme service environ-
ments, superior chemical resistance, wear resistance, and loading properties)
There are several types of materials currently called high-performance mate-
rials, for instance high-performance concrete, high-performance composites, high-
performance plastics, high-performance aluminum, high-performance ceramics,
and high-performance steel. What they all have in common is that they have
outstanding properties compared to the materials we used earlier. In short time
9
maybe the materials we know as HPM today may not be so high-performance
tomorrow, since the materials-science is rapidly changing and growing.
While research laboratories are still exploring ways to exploit these materi-
als, some of them are ready for use. Because there is little data available on the
long-term results of many high-performance materials and because there is fre-
quently a relatively high initial cost, states are reluctant to take on such a venture
independently.
Questions:
What is the conventional way of making a classification of materials?
What is the new way of making a classification of materials?
What is so special about high performance materials?
References:
High-performance materials:
http://www.hiper-group.com/hcproducts.htm
http://www.greatachievements.org/?id=3809
free internet books:
http://books.nap.edu/
10
1. Ceramics and glasses
A ceramic is often broadly defined as any inorganic nonmetallic material. By this
definition, ceramic materials would also include glasses; however, many materials
scientists add the stipulation that ”ceramics” must also be crystalline. Recall
that crystalline materials have their molecules arranged in repeating patterns, see
Figure 1.1. Therefore we often divide the ceramics and glasses into two separate
Figure 1.1: Crystalline structure.
subgroups of materials.
1.1. Ceramics
Examples of ceramic materials can be anything from NaCl (table salt) to clay
(a complex silicate).The term ceramic comes from the Greek word keramikos,
which means burnt stuff, indicating that desirable properties of these materials
are normally achieved through a high-temperature heat treatment process called
firing. Ceramics are refractory (fireproof) materials, and has therefore a melting
temperature > 1580◦C.
Due to the covalent character of the chemical bond refractory ceramics exhibit
very high (about 3000◦C) melting point, low mobility of atoms, low plasticity
and high hardness at temperatures up to 2000◦C. Therefore, refractory materi-
als can substitute metals, alloys and intermetallics in a lot of high temperature
engineering, chemical and electronic applications.
Ceramics are in general hard, brittle, high-melting-point materials with low
electrical and thermal conductivity, low thermal expansion, good chemical and
thermal stability, good creep resistance, high elastic modulus, high compressive
strength, low density, high stiffness, high hardness, high wear resistance, and high
11
corrosion resistance. Many ceramics are good electrical and thermal insulators.
Some ceramics have special properties: some ceramics are magnetic materials;
some are piezoelectric materials; and a few special ceramics are superconductors
at very low temperatures. Ceramics are widely used in the electrical industry
mostly due to their high electrical resistance. Ceramics and glasses have one
major drawback: they are brittle. Their extremely low fracture toughness is the
drawback of ceramics in comparison with metals. It means that ceramics have a
very low tolerance of crack-like flaws.
Ceramic fibers such as graphite and aluminum oxide with their extremely high
stiffness have led to the production of fiber-reinforced composites. These materials
are only a few of an ever-growing list of industrially important ceramics. Recently,
new groups of ceramics have emerged with the possibility to use them as load-
bearing materials.
1.2. Glasses
Glass is an inorganic nonmetallic material that does not have a crystalline struc-
ture. Such materials are said to be amorphous. Recall that amorphous materials
have their molecules arranged randomly and in long chains which twist and curve
Figure 1.2: Amorph structure.
around one-another, making large regions of highly structured morphology un-
likely, see Figure 1.2. Examples of glasses range from the soda-lime silicate glass
in soda bottles to the extremely high purity silica glass in optical fibers.
The major raw material of glass is sand (or "quartz sand") that contains
almost 100 % crystalline silica in the form of quartz. Most glass formulations
contain about 70—72 % by weight of silicon dioxide (SiO2). Soda-lime glass which
is the most common form of glass contains nearly 30 % sodium and calcium oxides
12
Figure 1.3: A transmission cable containing hundreds of glass optical fibers.
or carbonates. Pyrex is borosilicate glass containing about 10 % boric oxide. Lead
crystal is a form of lead glass that contains a minimum of 24 % lead oxide.
Large natural single crystals of quartz are pure silicon dioxide, and upon crush-
ing are used for high quality specialty glasses. Synthetic amorphous silica, an
almost 100 % pure form of quartz, is the raw material for the most expensive
specialty glasses.
1.3. Industrial Importance of Ceramics and Glasses
Silicon [Si] (do not confuse it with Silicone which are mixed inorganic-organic
polymers) has many industrial uses, for instance is it the principal component
of most semiconductor devices (whose electrical conductivity is in between that
of a conductor and that of an insulator), most importantly integrated circuits or
microchips. Silicon has been THE material which has made computers possible.
In the form of silica and silicates, silicon forms useful glasses, cements, and
ceramics. It is also a component of silicones, a class-name for various synthetic
plastic substances made of silicon, oxygen, carbon and hydrogen, often confused
with silicon itself.
Glasses have historically been used for low technology applications such as
soda bottles and window panes. However, glasses, like ceramics, have recently
found new application in high technology fields (particularly the semiconductor
microelectronics industry where silica is widely used as an insulator in transistors
and the fiber optic cable industry where high purity silica glass has made advanced
telecommunications possible, see Figure 1.3).
As with ceramics, the list of industrially important glasses also continues to
grow. As a result of their unique properties, ceramics and glasses are materials
which will be used extensively in areas such as aerospace, automobiles, microelec-
tronics, and telecommunications.
13
1.4. Industrially Important Glasses
Silicon [Si] (do not confuse with Silicone which are mixed inorganic-organic poly-
mers) has many industrial uses, for instance is it the principal component of
most semiconductor devices (whose electrical conductivity is in between that of
a conductor and that of an insulator), most importantly integrated circuits or
microchips.
In the form of silica and silicates, silicon forms useful glasses, cements, and
ceramics. It is also a component of silicones, a class-name for various synthetic
plastic substances made of silicon, oxygen, carbonand hydrogen, often confused
with silicon itself.
• Silica glass (SiO2) is used for optical fibers when it is very pure.
• Soda-lime glass (SiO2-Na2O-CaO) is the standard glass used for bottles and
windows due to its low cost and easy manufacturing.
• Borosilicate glass (SiO2-B2O3) is good in applications where thermal shock
resistance is necessary (e.g. laboratory glassware) because of its low coeffi-
cient of thermal expansion
• Lead glass (SiO2-PbO) commonly known as ”crystal”, this glass has a high
index of refraction causing it to sparkle (much like a diamond)
1.5. Technical Ceramics
Technical Ceramics covers ceramic materials and products for technical applica-
tion. Terms such as:
· functional ceramics (Components which fulfill an electrical, magnetic, dielectri-
cal, optical etc. function)
· structural ceramics, engineering ceramics, or industrial ceramics (Components
which are subjected mainly to mechanical loads.)
· electro-ceramics
· cutting ceramics
· bio-ceramics
· high-performance ceramics (see below)
describe the products groups of Technical Ceramics, but due to overlapping
there is not a clear classification.
14
Figure 1.4: Products made of ceramic material.
1.5.1. High-performance ceramics
High-performance ceramics are ceramics with incredibly light weight, high hard-
ness, non-corrodable, high melting points, high price and advanced applications,
see Figure 1.4.
Components made from high-performance ceramics are often determining the
functionality of machinery by possessing excellent corrosion resistance, very high
thermal stability and wear resistance, as well as high biocompatibility. Density,
porosity, electrical and optical characteristics can be varied within a wide range.
Highly specialized and flexible production techniques enable us to match our prod-
ucts to the specific customer demands.
In ENV 12212 (classification system for European comity for standardiza-
tion, CEN) high-performance ceramics are defined as ”highly developed, high-
performance applicable ceramic material, which is mainly non-metallic and inor-
ganic, and has certain functional properties.” The term is seen as a differentiation
to traditional clay based ceramic that includes china-ware, sanitary ceramic tiles
and bricks and covers all technical ceramics. The materials for electrical engineer-
ing are standardized according to the international standard IEC 627 (Interna-
tional Electrotechnical Commission, IEC).
The terms used above are often still used in classify technical ceramics. How-
ever a precise classification is only possible if the materials are listed under their
following chemical composition:
• silicate ceramics
— technical porcelain (quartz, feldspar and kaolin. )
15
— steatite (major component: soapstone, additives: clay and flux)
— cordierite (these magnesium silicates occur during the sintering of soap-
stone with added clay, kaolin, corundium and mullite.)
— mullite-ceramic (Al2O3 and SiO2,where mullite: (3 Al2O3 2 SiO2) and
corundium (Al2O3) )
• oxide ceramics
— aluminium oxide (AL2O3)
— magnesium oxide (MgO)
— zirconium oxide (ZrO2)
— aluminium titanate (AT)
— piezo ceramic (PZT), (the most important piezoelectrical ceramic ma-
terials are based on the oxide mixed crystals system lead zirconate and
lead titanate)
• nonoxide ceramics:
— carbide: Silicon carbide (SIC), Sintered silicon carbide (SSIC), Reac-
tion bonded silicom infiltrated silicon carbide (SSIC), Recrystallized
silicon carbide (RSIC), and Nitride bonded silicom carbide (NSIC)
— nitride: Silicon nitride (Si3N4), Silicon aluminium oxynitride (SIALON),
and Aluminium nitride (ALN).
Questions:
•What is the special properties of ceramics and glasses?
•What are they used for?
•What are the industrally important glasses?
•What kind of different ceramics are there?
•What is a high-performance ceramic?
•What is the drawback of ceramics compared to metals?
References:
http://www.keramverband.de/keramik/englisch/fachinfo/
werkstoffe/definitionen.htm
16
http://www.globaltechnoscan.com/
31stOct-6thNov02/high_performance_ceramics.htm
http://www.globaltechnoscan.com/
http://www.sciam.com/explore_directory.cfm
http://www.mse.cornell.edu/courses/engri111/ceramic.htm
http://www.mse.cornell.edu/courses/engri111/impglass.htm
http://biotsavart.tripod.com/327.htm
http://www.engr.sjsu.edu/WofMatE/
17
Figure 2.1: A suspension bridge.
2. Metals and metal alloys
Metals are elements that generally have good electrical and thermal conductivity.
Many metals have high strength, high stiffness, and have good ductility. Some
metals, such as iron, cobalt and nickel are magnetic. Many metals and alloys have
high densities and are used in applications which require a high mass-to-volume
ratio.
At extremely low temperatures, some metals and intermetallic compounds be-
come superconductors (a superconductor can conduct electricity without electrical
resistance at temperatures above absolute zero. The change from normal electrical
conductivity to superconductivity occurs suddenly at a critical temperature Tc).
Pure metals are elements which comes from a particular area of the periodic
table. Examples of pure metals include copper in electrical wires and aluminum
in cooking foil and beverage cans.
Metal Alloys contain more than one metallic element. Their properties can be
changed by changing the elements present in the alloy. Examples of metal alloys
include stainless steel which is an alloy of iron, nickel, and chromium; and gold
jewelry which usually contains an alloy of gold and nickel.
Some metal alloys, such as those based on aluminum, have low densities and
are used in aerospace applications for fuel economy. Other examples: Many metal
alloys also have high fracture toughness, which means they can withstand im-
pact and are durable. Many beverage cans are made of aluminum metal. Many
structures, such as this suspension bridge, are made of steel alloys, see Figure
2.1. Aircraft skins are made of lightweight aluminum alloys with high fracture
toughness.
18
2.1. High-peformance Metals
When metal components must perform under critical conditions, manufacturers
need high-performance metals. Titanium-base alloys, and specialty steels for the
aerospace industry are metals of exceptional wear resistance, corrosion resistance,
heat resistance, toughness, and strength. Nickel- and cobalt-based materials are
known as superalloys. Turbine blades are for instance made of superalloys in
order to withstand the temperatures well above 2,000◦ F (1093.3◦C). The most
advanced of these turbine blades are grown from molten metal as single crys-
tals in ceramic molds, in order to obtain maximum possible resistance to high-
temperature deformation.
2.1.1. High-Performance Aluminum
Aluminum bridge decks have a number of advantages over concrete and steel decks.
Aluminum is about 80 percent lighter than concrete. This substantial weight
savings allows many bridges to be strengthened without extensive reengineering
of substructures.
Aluminum requires fewer welds than steel, eliminating many potential failure
points. Compared to steel, aluminum is less expensive, both in the short term and
the long term. An aluminum deck is also more resistant to corrosion and other
environmental degradation.
Aluminium alloys are often used in Defense and Aerospace, which is one of
the most demanding industries, see Figure 2.2. These industries use high strength
5xxx series (Al-Mg) which are non-heat treatable base alloys for some applications,
but also make use of some of the more specialized heat treatable aluminum alloys
with superior mechanical properties.
Aluminum armor plating is used for its impact strength and strength-to-weight
ratio, and here alloy 5083, 7039 (Al-Zn) and and 2519 (AL-Cu ) are used as base
materials. Missiles are constructedof alloys 2019 and 2219. Perhaps the most
exotic aluminum alloys, with exceptional strength over a wide range of operating
temperatures, are used in the aerospace industry. Some of these alloys are 2219,
2014, 2090, 2024, and 7075. These base materials are typically used in specialized
high performance applications and have their own welding characteristics and
associated problems that require special considerations when joining.
19
Figure 2.2: Aerospace industry.
2.1.2. High-Performance Steel
A new grade of high performance steel, HPS-485W or HPS-70W, uses a new
chemical composition that provides improved welding and toughness properties.
The increase in strength and performance will allow targeted use of HPS that will
extend the useful life of steel bridge structures; and even greater savings with the
reduction of the total steel weight.
Structural components in new cars are for example made from high-performance
steel that is 3 times stronger than ordinary steel (900 MPa instead of 300 which
is ususal). This makes the new cars very crash resistant such that the passengers
are much more protected if there should be a collision.
2.1.3. Space-age metals
In jet aircrafts, rockets, missiles and nuclear reactors, the metals columbium (Nb,
41), titanium (Ti, 22), hafnium (Hf, 72), zirconium (Zr, 40) and tantalum (Ta,
73) are used. Columbium (niobium) can withstand high temperatures and can be
used for the skin and structural members of aerospace equipment and missiles. It
is a lightweight metal and a superconductor of electricity (which means that it
could be possible to use it in storing and transferring large amounts of energy in
the future). Titanium is as strong as steel and 45% lighter, and is often used for
jet engine components (rotors, fins, and compressor parts) and other aerospace
20
parts. Hafnium and zirconium are always found together are they make it possible
to control nuclear reactors in a precise way. The superior corrosion resistance of
zirconium makes it (and its alloys) very useful in the chemical industry and for
surgical implants. Pure zirconium has for a long time been used as the light
source in photo flash tubes, since it is a reactive metal that burns in air with a
brilliant white light. Tantalum (often occurs as the mineral columbitetantalite) is
very malleable and ductile. Its melting point is at 2996
◦
C, and is often used as a
replacement for platinium in chemical, and dental equipment and instruments. It
is also used to make electrolytic capacitors and are used in vacuum furnaces.
A superconducting material transmits electricity with virtually no energy loss.
Superconductivity, which occurs in many metals and alloys, is very new and is
therefore not yet in widespread use. Superconductivity is a phenomenon occurring
in certain materials at extremely low temperatures, characterized by exactly zero
electrical resistance and the exclusion of the interior magnetic field (the Meiss-
ner effect). Superconductivity occurs in a wide variety of materials, including
simple elements like tin and aluminium, various metallic alloys and some heavily-
doped semiconductors. Superconductivity does not occur in noble metals (metals
that are resistant to corrosion or oxidation, for instance gold, silver, tantalum,
platinum, palladium and rhodium; unlike most base metals), nor in most ferro-
magnetic metals.
Questions:
•Why are metals and metal alloys used?
•What is so special about high performance metals?
• In the space-age, what features in a material or material structure would be
important in the future?
•What kind of metals are used in space equipment, and why are they used?
References:
http://www.mse.cornell.edu/courses/engri111/metal.htm
http://www.allvac.com/
http://www.greatachievements.org/
http://www.hiper-group.com/hcproducts.htm
http://www.spacedaily.com/news/materials-02zh.html
http://www.alcotec.com/ataafi.htm
http://www.weldreality.com/aluminumalloys.htm
High Performance Steel Designers’ Guide:
http://www.fhwa.dot.gov/bridge/guidetoc.htm
21
http://www.mmc.co.jp/alloy/english/products/taisyoku/gijyutsu3.html
R. Gregg Bruce, Mileta M. Tomovic, John E. Neely and Richard R. Kibble, Mod-
ern materials and manufacturing processes, ISBN: 0-13-186859-4, Second edition,
Prentice Hall, 1998.
22
Figure 3.1: Polymerization by addition of equal monomers.
3. Polymers and Plastics
Polymer etymology: The word polymer comes from Greek: poly means ‘many’
and mer comes from merous which roughly means ‘parts’. Polymers are organic
materials characterized by long chain-like molecules built up from many units
(monomers), see Figure 3.1, generally repeated hundreds or thousands of times.
All atoms in a chain are bonded by covalent bond to each other, while Van der
Waals bonding keeps the chains together. Starch, cellulose, and proteins are
natural polymers. Nylon and polyethylene are synthetic polymers.
From organic chemistry, polymer is defined as: ”a large molecule formed by
the union of at least five identical monomers; it may be natural, such as cellulose
or DNA, or synthetic, such as nylon or polyethylene; polymers usually contain
many more than five monomers, and some may contain hundreds or thousands of
monomers in each chain.”
3.1. The structure of polymers
Polymerization is the word for the process of forming large molecules from small
molecules. When there are no possibility to add any more atoms, the molecules
are said to be saturated. When molecules do not have the maximum number
of atoms, because atoms in the molecule are held together with double or triple
covalent (shared) bonds, they are called unsaturated. The unsaturated molecules
are important in the polymerization process, which means that small molecules
are linked together to form large molecules, as you can see in Figure 3.1, where
the process has taken place through addition mechanism. Here, a large molecule
23
Figure 3.2: Methane and ethane.
(polymer) is formed by a repeated unit (mer). Activators or catalysts (benzoyl
peroxide) are often required to drive the reaction. A polymer can also be made
from a condensation process which means that reactive molecules combine with
one another to produce a polymer plus small, by-product molecules, such as water.
Often, heat, pressure or a catalyst are required to drive the reaction. In most
commercial available plastics the number of mers in the polymer (which is known
as the degree of polymerization) range from 75 to 750. When two different types of
mers are combined into the same addition chain, we call them copolymers. And,
in terpolymers three different monomers are included.
The molecular structure of polymers are often based on paraffin-type hydro-
carbons where carbon and hydrogen are linked in the relationship
CnH2n+2,
as we see in Figure 3.2. Hydrogen can be replaced by chlorine, flouring and also
benzene. Carbon can be replaced by oxygen, silicon, sulfur or nitrogen. These
possibilities are the reason why a wide range of organic compounds can be created.
By the description of polymers we see that wood (cellulose-type materials, see
Figure 3.3) are included in the group of polymer. It has been accepted for many
years that cellulose is a long chain polymer, made up of repeating units of glucose,
a simple sugar. As a carbohydrate, the chemistry of cellulose is primarily the
chemistry of alcohols; and it forms many of the common derivatives of alcohols,
such as esters, ethers, etc. These derivatives form the basis for much of the
industrial technology of cellulose in use today. Cellulose derivatives are used
commercially in two ways, as transient intermediates or as permanent products.
24
Figure 3.3: The structure of cellulose.
3.2. Crystallinity in polymers
We need to distinguish between crystalline (see Figure 1.1) and amorphous ma-
terials (see Figure 1.2) and thenshow how these forms coexist in polymers. The
reasons for the differing behaviors lie mainly in the structure of the solids.
The morphology of most polymers is semi-crystalline. That is, they form mix-
tures of small crystals and amorphous material, see Figure 3.4 and melt over a
range of temperature instead of at a single melting point. The crystalline mate-
rial shows a high degree of order formed by folding and stacking of the polymer
chains. The amorphous or glass-like structure shows no long range order, and the
Figure 3.4: A polymer with the combination of amorphous and crystalline areas, from:
http://plc.cwru.edu/tutorial/enhanced/files/polymers/orient/orient.htm
25
chains are tangled. There are some polymers that are completely amorphous, but
most are a combination with the tangled and disordered regions surrounding the
crystalline areas. Most thermoplastics have crystalline regions alternating with
amorphous regions, while
3.2.1. The glass transition temperature and melting temperature
The glass transition temperature Tg (also called the glass temperature), describes
the temperature at which amorphous polymers undergo a second order phase tran-
sition from a rubbery, viscous amorphous solid to a brittle, glassy amorphous solid.
Tg is a property of amorphous polymers which do not have a sharp melting point,
and is defined as the temperature at which the specific volume vs temperature plot
has a change in slope, see Figure 3.5. When we cool an amorphous material from
the liquid state, there is no abrupt change in volume such as occurs in the case
of cooling of a crystalline material through its freezing point, Tf (=Tm). Instead,
at the glass transition temperature, Tg, there is a change in slope of the curve of
specific volume vs. temperature, moving from a low value in the glassy state to a
higher value in the rubbery state over a range of temperatures. This comparison
between a crystalline material (1) and an amorphous material (2) is illustrated in
Figure 3.5. Note that the intersections of the two straight line segments of curve
(2) defines the quantity Tg. When a polymer is cooled below Tg, the molecules
have little relative mobility, and the material becomes hard and brittle, like glass.
Some polymers are used above their glass transition temperatures, and some are
used below. Tg is usually referred to wholly or partially amorphous phases in
glasses and polymers. As the temperature of a polymer drops below Tg, it be-
haves in an increasingly brittle manner. As the temperature rises above the Tg,
the polymer becomes more rubber-like. In general, values of Tg well below room
temperature define the domain of elastomers and values above room temperature
define rigid, structural polymers.
The glass transition is not the same thing as melting. Among synthetic poly-
mers, (crystalline) melting temperature Tmcrystalline melting is only discussed
with regards to thermoplastics, as thermosetting polymers will decompose at high
temperatures rather than melt. Tm (also called flow temperature for amorphous
materials) happens when the polymer chains fall out of their crystal structures,
and become a disordered liquid.
Even crystalline polymers will have a some amorphous portion. This portion
usually makes up 40-70% of the polymer sample. This is why the same sample of a
26
Figure 3.5: Comparison between a crystalline material (1) and an amorphous material
(2). From: http://plc.cwru.edu/tutorial/enhanced/files/polymers/therm/therm.htm
polymer can have both a glass transition temperature and a melting temperature.
But you should know that the amorphous portion undergoes the glass transition
only, and the crystalline portion undergoes melting only.
According to Wikipedia, the disaster of the space Shuttle Challenger was
caused by rubber O-rings that were below their Tg, on an unusually cold Florida
morning, and thus could not flex enough to form proper seals between sections
of the two solid-fuel rocket boosters (SRB), see Wikipedia. SRB’s are used to
provide the main thrust (reaction force) in spacecrafts launches from the earthe
up to about 45 kilometres.
Polymer science is a broad field that includes many types of materials which
incorporate long chain structure of many repeat units as discussed above. The
two major polymer classes are:
• Elastomers
• Plastics
Another important property of polymers, also strongly dependent on their
temperatures, is their response to the application of a force, as indicated by two
27
Figure 3.6: Plastics.
main types of behavior: elastic and plastic. Elastic materials will return to their
original shape once the force is removed. Plastic materials will not regain their
shape. In plastic materials, flow is occurring, much like a highly viscous liquid.
Most materials demonstrate a combination of elastic and plastic behavior, showing
plastic behavior after the elastic limit has been exceeded.
3.3. Plastics
Plastics, see Figure 3.6, are a large group of polymers that has properties between
elastomers and fibers, and has plastic behavior. As such, plastics have a wide
range of properties such as flexibility and hardness and can be synthesized to
have almost any combination of desired properties.
Plastics are polymers which, under appropriate conditions of temperature and
pressure, can be molded or shaped (such as blowing to form a film). In contrast
to elastomers, plastics have a greater stiffness and lack reversible elasticity. All
plastics are polymers but not all polymers are plastics.
Cellulose is an example of a polymeric material which must be substantially
modified before processing with the usual methods used for plastics. Every day
plastics such as polyethylene and poly(vinyl chloride) have replaced traditional
materials like paper and copper for a wide variety of applications.
3.4. Properties of plastics
New types of plastics are developed all the time, and therefore it is helpful to have
a brief knowledge of the following general basic properties of plastics.
28
• Light weight: Most plastics have a specific gravity (SG) between 1.1 and
1.6. Magnesium has a SG about 1.75. Specific gravity is the heaviness of
a substance compared to that of water, and it is expressed without units. In
the metric system specific gravity is the same as in the English system. If
something is 7.85 times as heavy as an equal volume of water (such as iron
is) its specific gravity is 7.85. Its density is 7.85 grams per cubic centimeter,
or 7.85 kilograms per liter, or 7.85 metric tons per cubic meter.
• Corrosion resistance: Many plastics perform well in hostile, corrosive
environments.
• Electrical resistance: Plastics are often used as insulating materials.
• Low thermal conductivity: Plastics are relatively good thermal insula-
tors.
• Variety of optical properties: You can get a plastic in almost any color
you would like, and the color can go throughout (not only at the surface).
You can also get transparent or opaque plastics.
• Formability: Plastics are easy to form (often in only one single operation).
Extrusion, casting and molding are widely used.
• Surface finish: You can get the surface you want, from rough to excellent
surface finish.
• Comparatively low cost: Both material and processing/manufacturing
processes are cheap. Tool costs are also low.
• Low energy content: Plastics melt at low temperature compared with
metals, and are therefore produced with little energy.
The mechanical strength of plastics are not especially high, compared to met-
als, but the low density makes them comparable to metals due to their strength-
to-weight ratio (or specific strength). A material has high specific strength if the
ratio of its strength to its weight is high.
Plastics are usually divided into two main groups: thermosettings or thermo-
plastics. The terms refer to the materials responseto elevated temperature. It is
important to know whether the plastic is a thermosetting or a thermoplastic since
it determines how the plastic will perform in service.
29
3.4.1. Thermosettings
In some plastics, polymerization produces cross linkage between long molecular
weight chain molecules. These plastics are known as thermosetting plastics be-
cause they are permanently hardened by heat. The setting process is irreversible,
so that these materials do not become soft under high temperatures. Additional
heating do not lead to softening, but the material maintain their mechanical prop-
erties up to the temperature at which they char, or burn.
Thermosetting plastics usually have a highly cross-linked or three dimensional
framework structure in which all atoms are connected by strong, covalent bonds.
They are generally produced by the process of condensation polymerization where
elevated temperature promotes the irreversible reaction, hence the term thermoset-
ting.
The thermosettings are stronger and more rigid than the thermoplastics, but
have a lower ductility and poorer impact properties. These plastics also resist
wear and attack by chemicals and they are very durable, even when exposed to
extreme environments.
Typical thermosetting-type plastics are the aminos, most polyesters, alkyds,
epoxies, phenolics and urethanes.
3.4.2. Types of Thermosettings
PUR - Polyurethane/polyurethene (or PU)
PUR is found in a variety of forms ranging from stiff to soft types. Stiff PUR is
used for casings and modelling material (artificial wood). Softer rubber-like PUR
is used for handtools. Expanded PUR is used for mattresses and car inner panels
where it both forms the foam and the leather-like skin. Expandable insulation
foam and moisture hardening glue are also made from PUR. Large parts are often
made from PUR due to low tooling cost. In general it has excellent outdoor
performance and resistance to most acids and solvents.
Genoa stacking chair. PUR can be made from a wide variety of raw materials
to give hard, clear resins for surface coating: soft flexible resins for oil resistant and
abrasion resistant rubbers; rigid or flexible foams for thermal insulation, cushion
and fabric stiffeners. In building surface coating and thermal insulation are their
main applications.
Products: Mil-Tek high pressure cleaner, Panton chair, Shoe soles, and it is
used as modelling material (produced by Westnofa) in the Product Design course
at HiN .
30
EP - Epoxy
Epoxy is a strong and very resistant thermoset plastic. It is used as an adhesive
agent, as filling material, for moulding dies, and as a protective coating on steel
and concrete. Many composite materials are reinforced epoxy.
Epoxy is resistant to almost all acids and solvents, but not to strong bases or
solvents with chlorine content.
By adding a hardening agent curing takes place. The type of hardener has a
major influence on properties and applications of epoxies.
Products: Surfing board, Composite bicycle, Badminton racket, Wheel chair,
Knee support, Soda stream pressure, container, Skull, model, Car space frame,
Wheel chair ramp, Swing wheel.
UP - Unsaturated Polyester
UP is widely used as filler material with glass fibre in sailing boats, hard tops
for cars, furniture, etc. In general UP is not resistant to solvents and bases.
Apart from sulphuric acid it resists acids. To improve appearance and resistance
a surface layer (gel coat or paint) is often added. UP does not require expensive
equipment or tooling to work with UP, and it is therefore often used for prototypes
and low-volume production.
Products: Sailing boat, Chair, Hard top for car, Printed circuit board, Pedes-
trian bridge.
UF - Urea formaldehyde
Urea thermoset molding compounds offer a wide range of applications for
every-day living and industry. Urea formaldehyde (UF) thermosets are economi-
cally priced, they are strong, glossy, and durable. They are not affected by fats,
oils esters, ether, petrol, alcohol or acetone, nor by detergents or weak acids, and
they exhibit good resistance to weak alkalis.
Their high mechanical strength, heat and fire resistance, and good electrical
arc and tracking resistance make them an ideal plastic for numerous industrial and
household applications, from doorknobs and toilet seats to electrical components
and cosmetics enclosures. You name it — if it can be plastic, it can be stronger
and brighter as a (Perstorp) urea thermoset.
MF - Melamine formaldehyde
Melamine thermoset plastics are similar to urea molding compounds, but
melamine has even better resistance to heat, chemicals, moisture, electricity and
scratching.
31
Melamine formaldehyde (MF) thermosets are ideal for dinnerware, kitchen
utensils, bathroom accessories, and electrical components. The molded com-
pounds are bright, inviting, and highly resistant to scratches and staining. (Per-
storp’s) melamine thermosets are approved for contact with foodstuffs, and they
do not affect the food’s flavor - even at high temperatures. They are very, very
durable.
Like urea molding compounds, melamine thermosets consist of plastic that has
high surface hardness and gloss, brilliant and precise colors, and light fastness.
UF or MF thermosets can be manufactured in a precise and vibrant array of
colors. Two-tone compression molding using doublepunch tools will enable you
to express your creative designs. For example, your cups or sinks can have white
inside and tasteful color outside. The choice of color and shape is limited only by
your imagination.
Alkyd resins
This group of polyesters are usually compression moulded from powders. Orig-
inally produced for inclusions in paints, they are resistant to heat and electricity
and will withstand attack by acids and solvents. Alkyd plastics find applications
in enamels for cars, refrigerators and washing machines and are also used for
electric motor insulation and some television parts.
Silicones
Silicon is an element whose atoms have similar linking properties to those of
carbon, but it is stable at much higher temperatures. To utilize the properties of
silicon, certain plastics, called silicones have been developed based on the element.
Although they are much more expensive, they contain excellent properties. These
super materials are available as oil, plastics and rubbers. To quote an example
illustrating their value: silicone rubber will retain its elasticity over a temperature
range of -80◦C to 250◦C. The stability of silicones under widely varying service
conditions make them valuable materials for applications such as laminates in the
aerospace industry, gaskets and seals for engineering purposes and cable insulation
for aircraft electrical systems.
3.4.3. Thermoplastics
Thermoplastics, alternatively thermosoftenings, as the name implies, are hard at
low temperatures but soften when they are heated. The softening and hardening
can be repeated without any change in the chemical structure. Although they are
32
Figure 3.7: The easiest way to identify the type of thermoplastic you’re working with
is to look for the Plastic ID symbol the backside of the part.
less commonly used than thermosetting plastics they do have some advantages,
such as greater fracture toughness, long shelf life of the raw material, capacity for
recycling and a cleaner, safer workplace because organic solvents are not needed
for the hardening process.
Thermoplastics have weak bonds between the neighboring molecules and they
are weakened by elevated temperature which means they soften at high temper-
ature and are stronger and harder when cooled. They do not have any definite
melting temperature, they have a range of temperatures where they soften. When
cooled below the glass transition temperature, Tg, the linear polymer retains its
amorphous structure, but becomes hard, brittle, and glasslike.Thermoplastics are not cross-linked and can be softened and hardened over and
over again. The majority of polymers are thermoplastic. Today there are primar-
ily six commodity polymers in use, namely polyethylene terephthalate (PETE),
polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene
(PS) and polycarbonate (PC). These make up nearly 98% of all polymers and
plastics encountered in daily life, see ref.[33].
The Society of the Plastics Industry, Inc. (SPI) introduced its resin identifica-
tion coding system in 1988 at the urging of recyclers around the country. The SPI
code was developed to meet recyclers needs while providing manufacturers a con-
sistent, uniform system that could apply nationwide, see figure 3.7. Look at the
bottom of a recyclable plastic bottle - chances are you will see a PE or PS which
means polyethylene or polystyrene. These materials are examples of what happens
33
to polymers when they solidify: the chains are entangled and packed together to
make light, tough, flexible materials. If you heat up PE or PS to moderate tem-
peratures, if the chains have not been chemically stuck together (‘cross-linked’)
they will melt, and turn into goopy liquids, which are called polymer melts. Some
polymers melts even at room temperature, like polydimethylsiloxane (PDMS), or
poly(ethylene-propylene) (PEP).
3.4.4. Types of Thermoplastics
PET - Polyethylene terephthalate (or PETE)
PET has good barrier properties against oxygen and carbon dioxide. There-
fore, it is utilized in bottles for mineral water. Other applications include food
trays for oven use, roasting bags, audio/video tapes as well as mechanical compo-
nents.
PET exists both as an amorphous (transparent) and as a semi-crystalline
(opaque and white) thermoplastic material. Generally, it has good resistance
to mineral oils, solvents and acids but not to bases.
The semi-crystalline PET has good strength, ductility, stiffness and hardness.
The amorphous PET has better ductility but less stiffness and hardness.
Danish Name PET - thermoplastic polyester
Products: Bottle for mineral water, Trays for oven use, Oven foils, Audio and
video tapes, Thermo scarf (fleece)
PE - Polyethylene
PE is a semi-crystalline thermoplastic material and one of the most commonly
used plastics. It is generally ductile, flexible and has low strength. PE is one
of the most commonly used thermoplastic material due to the good properties
combined with a low price.
There are two basic families: LDPE (low density), and HDPE (high density):
• LDPE - low density polyethylene: LDPE is the low density version of
PE. This has less hardness, stiffness and strength compared to HDPE, but
better ductility. It is opaque and only thin foils can be transparent. LDPE
is used for packaging like foils, trays and plastic bags both for food and
non-food purposes. Used as protective coating on paper, textiles and other
plastics, for instance in milk cartons. Products: Wrapping foil for packaging,
Plastic bag (soft type that does not crackle), Garbage bag, Tubes, Ice cube
plastic bag.
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• HDPE - high density polyethylene: HDPE is the high density version
of PE plastic. It is harder, stronger and a little heavier than LDPE, but less
ductile. Dishwasher safe. HDPE is lighter than water, and can be moulded,
machined, and joined together using welding (difficult to glue). The appear-
ance is wax-like, lusterless and opaque. The use of UV-stabilizators (carbon
black) improves its weather resistance but turns it black. Some types can be
used in contact with food. Products: Milestone, Bottle for motor oil, Bot-
tle for organic solvents, Street bollard, Hedge cutter, Gasoline tank, Milk
bottles, Plastic bag (stiff type that crackles), Children’s toys, Lid for honey
pot, Beer crate, Dolphin bicycle trailer.
PVC - Polyvinyl chloride (vinyl)
PVC is one of the oldest and most commonly used thermoplastic material, it
is a heavy, stiff, ductile and medium strong amorphous (transparent) material.
By adding softeners, a range of softer materials can be achieved, ranging from
a flexible to an almost rubber-like elastic soft material. Softeners also help to
increase the manufacturability. PVC has brilliant resistance to acids and bases,
but is affected by some solvents. Soft PVC is exceptionally resistant to most
chemicals. The poor weather resistance can be improved using additives. PVC
has good barrier properties to atmospheric gasses. PVC has a Tg of 83◦C, making
it good, for example, for cold water pipes, but unsuitable for hot water. PVC will
also always be a brittle solid at room temperature.
Products: Boat fender, garden hose, electrical wire insulation, vinyl flooring,
roof gutter, vinyl record, children’s doll, wrapping film, medical transparent tube,
Pneumatic chair.
PP - Polypropylene
PP is an inexpensive, ductile, low strength material with reasonable outdoor
performance. The material surface is soft wax-like and scratches easily. It has a
high stiffness, good strength even in relatively high temperatures, abrasion resis-
tant, good elastic properties and a hard glossy surface. In low temperatures PP
gets brittle (< 0◦C). Stiffness and strength are often improved using reinforcement
of glass, chalk or talc. The color is opaque and white, but it can be dyed in many
colors. In many ways, PP is similar to HDPE, but it is stiffer and melts at 165-
170◦C. PP can be manufactured by all the methods used for thermoplastics. PP
has high crystallinity (70-80 %), and is one of the lightest thermoplastics on the
marked. The chemical properties are good. PP is resistant to inorganic chemicals
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and water. It is resistant to most strong mineral acids and basics. PP is not
resistant to nitrous gasses, halogens and strong oxidizing acids.
Products: Childrens toy bin, transport box, fuel tank, suitcase, garbage bin,
rope, shaver (rechargeable), air intake, tubes, packing material, auto parts etc.
The material is often used for hinges as it can be flexed millions of times before
breaking.
PS - Polystyrene
Polystyrene is an inexpensive amorphous thermoplastics that has good me-
chanical proprieties. It is vitreous, brittle and has low strength. However it is
also hard and stiff. Foamed PS is used for packaging and insulation purposes.
PS is not weather resistant, and therefore not suitable for outdoor uses. PS is
transparent (it transmits about 90% of the sunlight) and has unlimited dyeing
possibilities. Assembly can be done with gluing.
Products: CD and MC covers, disposable drinking glass, glass for bicycle
lamp, salad bowl, razor (ordinary), razor (biodegradable), disposable articles,
signs, machine parts and picture frames etc.
PC - Polycarbonate
Polycarbonate is an amorphous plastic with very high impact strength, good
ductility and high stiffness. It is very difficult to break and the material is therefore
considered fracture-proof (e.g. bullet-proof glass).
Light transmission is 85-90% but depends on the thickness. It has good out-
doors resistance in the UV-stabilized form, but it tends to turn yellow by long
exposition to sunlight. PC is transparent and can be dyed in many colors. PC
has a relatively good chemical resistance.
Products: PC is commonly used for shielding of work places and machines,
sight glass, tubes etc. due to its transparency and high impact resistance, CD
compact disc, bullet-proof glass, water container.
ABS -Acrylonitrile-butadiene- styrene
Acrylnitrile contributes with thermal and chemical resistance, and the rub-
berlike butadiene gives ductility and impact strength. Styrene gives the glossy
surface and makes the material easily machinable and less expensive.
Generally, ABS has good impact strength also at low temperatures. It has sat-
isfactory stiffness and dimensional stability, glossy surface and is easy to machine.
If UV-stabilizators are added, ABS is suitable foroutdoor applications.
Products: LEGO building bricks, Computer mouse, Vacuum jug, KimBox
suitcase, Ceramic advanced wet shave razor, Hedge cutter handle, Handle for
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high pressure cleaner, Shaver, rechargeable, Ensemble chair (ABS blended with
PA), auto body parts, suitcases, toys etc. Extruded profiles, tubes and bolts can
be made from ABS when the requirements are high impact resistance and a nice
surface.
PA - Polyamide (nylon)
PA is a group of amorphous (transparent) and semi-crystalline (opal-white)
plastics. Arguments for using PA include strength (fishing line, axe handle),
wear resistance (bearings), barrier properties (food packaging) and machinability.
Polamide is recognised for good abrasion resistance, low friction coefficient, good
resistance to heat and good impact resistance. PA absorbs water which makes it
softer. UV-stabilizators are required for outdoor applications.
Products: Nylons (stockings), fishing line, bicycle trailer (rainproof cover),
bearing, axe, hedge cutter, handle for, high pressure cleaner, bottle for tomato
ketchup (barrier layer), ensemble chair (PA blended with ABS), bottle-opener.
Kevlar (aramid fibre) is a family of nylons.
Acrylic - PMMA (plexiglas)
PMMA (polymethyl-methacrylate) is an amorphous thermoplastic material
with very good optical properties (as transparent as glass and it allows 92% of
the sunlight to pass!).
PMMA is hard, stiff and medium strong, easy to scratch, notch sensitive,
but easy to polish and has a very good weather resistance. Exceptional outdoor
performance, such as weather and sunlight resistance, without reduction neither of
optical nor mechanical properties. PMMA is resistant to water, basics, inorganic
salts diluted in water, most diluted acids. It is not resistant to strong acids, basics
and polar solvents.
Products: Tail light glass, exhibition case, folding chair, kitchen scale, decora-
tion articles, transparent tubes, signs, windows, level glass etc..
POM - (polyoxymethylene) Acetal
Acetal is a crystalline plastic often used for technical applications due to its
strength, ductility and good machinability. It has good creep properties which
makes it suitable for click connections (e.g. bicycle lamp holder). It exhibits good
stiffness, strength and hardness up to 120◦C, and the elasticity is comparable
with that of many metals. Acetal is wear resistant and has a very low friction
coefficient. The color is opaque white. To protect it from UV-light carbon black
can be added, changing its color into black.
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Products: Vacuum jug (top), Holder for bicycle lamp, Fitting for Vico Duo
chair, Gearwheel.
PTFE - Fluoropolymer (Teflon)
Fluoropolymers can be used to make a variety of articles having a combination
of mechanical, electrical, chemical, temperature and friction-resisting properties
unmatched by articles made of any other material. Commercial use of these and
other valuable properties combined in one material has established TEFLON R°
resins as outstanding engineering materials for use in many industrial and mil-
itary applications. TEFLON R° resins may also be compounded with fillers or
reinforcing agents to modify their performance in use.
TEFLON R° PTFE resins have a continuous service temperature of 260◦C
(500◦F). Much higher temperatures can be satisfactorily sustained for shorter
exposures.
Teflon is used in: Food processing, Electrical parts, Coaxial cable connectors,
Terminal insulators, Transformers, Relays, Medical industry, Washers, Gaskets,
Flanges, Valve components, Pump Components, Baffles, Seals, Bearings, Rings,
Bushings , High heat applications. Teflon is available as: Sheets, Rods, Tubes,
Heavy wall tubing, Film, Rectangular bar, Pressure sensitive, tape.
TPUR - Thermoplastic urethane (or TPU)
TPU is a urethane based TPE (thermoplastic elastomer). It is made of long
chained molecules of diols and diisocyanates. Urethane is the unit which is re-
peated in polyurethane. TPU has a very good abrasion resistance. It is a tough
material with a good elasticity over a wide temperature range. TPU is filling the
gap between rubber material and the more traditional thermoplastics.
The electrical conductance is very low. TPU is a hygroscopic material, and
the conductance is dependent on the content of moisture. TPU is resistant to
oil, fat, gasoline, and ozone. It is not resistant to hot water, steam, strong acids
and basics. Polyether based TPU is resistant to microbes. TPU is available in a
variety of qualities.
Products: Bumpers, hoses, tubes, sleeves, cushions, coating, insulators, apron
rollers etc.
PEEK - Polyetheretherketone
PEEK is a high temperature resistant engineered thermoplastic with excel-
lent chemical and fatigue resistance plus thermal stability. They exhibit superior
mechanical and electrical properties. With a maximum continuous working tem-
perature of 249◦C (480◦F), they have excellent retention of mechanical properties
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up to 299◦C (570◦F) in a steam or high-pressure water environment. Superior
chemical resistance has allowed them to work effectively as a metal replacement
in harsh environments. They are inert to all common solvents and resist a wide
range of organic and inorganic liquids. When ∆extensive machining is required,
a secondary annealing process should be considered.
PEEK is an excellent material for a wide spectrum of applications where ther-
mal,chemical, and combustion properties are critical to performance. The addi-
tion of glass fiber and carbon fiber reinforcements enhances the mechanical and
thermal properties of the basic PEEK material.
Products: automobile engine parts, medical equipment, aerospace products.
Today there are primarily six commodity polymers in use, namely polyethylene,
polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene and
polycarbonate. These make up nearly 98% of all polymers and plastics encoun-
tered in daily life.
3.5. Classification
• Standard plastics used in non-critical and low-stress applications are mate-
rials like PS, ABS, PVC, PP, HDPE, and LDPE.
• Engineering plastics that are used in general structural, bearing and wear
purpose are plastics like PPO (Polyphenylene oxide, modified), Acrylic, PC
(Polycarbonate), PET-P (Polyethylene Terephtalate), POM (Poly-oxymethylene
=Acetal), PA (Polyamide = Nylon), and UHMW-PE (Ultra high mole wt.
Polyethylene).
• Advanced engineering plastics that have superior properties and can be
used in extreme environments are plastics like PSU (Polysulfone), PPSU
(Polyphenylsulfone), PEI (Polyetherimide), PTFE (Polytetraflouroethylene
= Teflon), PPS (Polyphenylene sulfide), PEEK (Polyetheretherketone), PI
(Polyimid), PAI (Polyamide-imide), and PBI (Polybenzimidazole).
3.6. Additives in Plastics
Very often, some additional materials are mixed into plastics, to obtain:
• improved properties
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• reduced cost
• improved moldability
• wanted color
These additional materials are classified as fillers, plasticizers, lubricants, color-
ing agents, stabilizers, antioxidants, flame retardants, foaming or blowing agents,
antifogging agents, antistatic agents, clarifying agents and optical brighteners.
New ones are added to the list continuously, so we briefly mention a few of them.
Fillers
Improve mechanical properties, reduce shrinkage, reduce weight or provide
bulk. Fillers comprise a large percentage of the total volume of the plastic. Ex-
ample of fillers can be: wood flour, cloth fibers, glass fibers, clay.
Plasticizers
Increase flexibility, improve flow during molding, reduce shrinkage, reduce
weight.
Lubricants
Comparison of both internal lubricants and external lubricants which can be
blended with various materials to reduce friction, and wear, improve mar resis-
tance, and extend the useful life of products which are subject to friction. They
also improve moldability andextraction from molds.
Coloring Agents
Coloring Agents are put in the plastic to Impart color.
Stabilizers
Stabilizers retard degradation due to heat or light.
Antioxidants
Antioxidants retard degradation due to oxidation.
Flame retardants
Flame retardants reduce flammability.
Foaming Agents
Foaming Agents, also known as Blowing or Nucleating Agents, can eliminate
sink marks, reduce density, shorten cycle time and reduce total production costs.
In extrusion and injection molding, foaming agents can save material weight and
lower total cost. They also improve extrusion rates by increasing the volume that
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can be processed per extruder in a given period of time, and endothermic foaming
agents absorb heat and improve injection molding cycle time.
Antifogging agents
Antifogging agents reduce the formation of condensed droplets on the surface
of polyolefin films, such as for food-packaging or agricultural films, resulting in
better film transparency and consequently providing better food preservation.
Antistatic agents
These new permanent antistatic agents, form a conductive network throughout
the polymer matrix which dissipates the electrical charge as it builds up. They
are already effective for processing and even work at low environmental humidity.
Clarifying agents/Optical brighteners
Clarifying agents/optical brighteners are designed to give brilliance and whiten-
ing to a variety of applications. Synthetic fibers for example, have an inherent
yellowish tint. Add optical brighteners and the fibers appear cleaner and whiter.
IRGACLEAR R° is a range of products that not only improves the clarity and
transparency of polypropylene, but also enhances the mechanical properties.
3.6.1. Oriented Plastics
The strength of the intermolecular bond increases with reduced separation dis-
tance, and that is why a processing that makes the molecules align parallel make
the long-chain thermoplastic higher strength in a given direction. This is called
an orientation process, and can be obtained by stretching, rolling, or extrusion, as
shown in the Figure 3.8. When a polymer (amorphous or crystalline) is subjected
to stress (tensile), the molecular chains become aligned or oriented parallel to the
direction of applied stress. The polymer is then in an oriented state. Orienting
may increase the tensile strength by more than 200%, but 25% is more typical.
3.7. Elastomers & Rubbers
Elastomers, or rubbery materials, have a loose cross-linked structure. Natural and
synthetic rubbers are both common examples of elastomers. Elastomers possess
memory, that is, they return to their original shape after a stress is applied.
Elastomers are amorphous polymers and consist of long polymer chains above
their glass transition temperature. The structure of elastomers is tightly twisted
or curled.
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Figure 3.8: Presentation of the alignment of the plastic molecules in the orienting
process.
Figure 3.9: Elastomers.
Elastomers are reversibly stretchable for small deformations. When stretched,
the polymer chains become elongated and ordered along the deformation direction.
When no longer stretched, the chains randomize again. The cross-links guide the
elastomer back to its original shape. They are very flexible and elastic, which
means that they can undergo large elastic deformations without ruptures and
recover substantially in shape and size after the load has been removed. Many
elastomers can be stretched to several times their original length. Also, the cycle
can be repeated numerous times with identical results, as with the stretching of
a rubber band.
Elastomers are generally resistant to oil and fuel, impermeable to liquids and
gases, but tend to deteriorate by oxidation.
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Like plastics, elastomers are either thermoplastic material (they can be remelted)
or thermoset material (that cannot be remelted). Rubber is an older name for
elastomers.
Elastomeric polymers do not follow Hooks’s law (as most engineering material
do). The behavior of the elastomers is a bit more complex due to the molecular
shape and the fact that small degree of viscous deformation in produced when
load is applied.
3.7.1. Rubber and Artificial Elastomers
The oldest commercial elastomer is natural rubber, which is made from a processes
sap of a tropical tree. Natural rubber (NR) is a biopolymer which is known as
polyisoprene. The rubber tree (Hevea brasiliensis) is the most common source of
natural rubber used today. Polyisoprene can also be synthesized by polymerization
from its monomer isoprene (CH2=C(CH3)CH=CH2), (IR). This is a rare example
of a natural polymer that we can make almost as well as nature does. Rubber has
been used for centuries by the South American Indians. They most probably were
the people who discovered that if latex (a milky fluid that circulates in the inner
portions of the bark of many tropical and subtropical trees and shrubs) is dried,
it can be pressed into useful objects such as bottles, shoes and balls. Figure 3.10
shows the common use of rubber.
However, it was not until the 1830s (when John Haskins and Edward Chaffee
organized the first rubber-goods factory in the United States) that the commer-
cial rubber industry really began to flourish. But rubber had many weaknesses;
it softened with heat and hardened with cold; it was tacky, odorous, and per-
ishable. In 1834 the German chemist Friedrich Ludersdorf and the American
chemist Nathaniel Hayward discovered that if they added sulfur to gum, then
rubber lessened or eliminated the stickiness of finished rubber goods. Charles
Goodyear discovered in 1839, that cooking natural rubber with sulfur removed
the gum’s unfavorable properties and could be strengthened by cross-linking it
with approximately 30% sulfer and heating it to a suitable temperature. This
process is called vulcanization, and led to many and varied applications of nat-
ural rubber, since the rubber then has got increased strength and elasticity and
greater resistance to changes in temperature. It is also impermeable to gases, and
resistant to abrasion, chemical action, heat, and electricity, in addition to have
high frictional resistance on dry surfaces and low frictional resistance on water-wet
surfaces. The vulcanization process remains fundamentally the same as it was in
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Figure 3.10: Common use of rubber.
1839.
Vulcanized rubber has numerous practical applications, such as
• excellent abrasion resistance which makes it valuable for the treads of vehicle
tires, conveyor belts (soft rubber), pump housings and piping used in the
handling of abrasive sludges (hard rubber).
• flexibility characteristics which makes it suitable for use in hoses, tires, and
rollers for a wide variety of devices ranging from domestic clothes wringers
to printing presses.
• its elasticity makes it suitable for various kinds of shock absorbers and for
specialized machinery mountings designed to reduce vibration. Since it its
relatively impermeable to gases its used as air hoses, balloons, balls, and
cushions.
• resistance to water and to the action of most fluid chemicals has led to its
use in rainwear, diving gear, and chemical and medicinal tubing, and as a
lining for storage tanks, processing equipment, and railroad tank cars.
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• high electrical resistance, soft rubber goods are used as insulation and for
protective gloves, shoes, and blankets. Hence, hard rubber is used for articles
such as telephone housings, parts for radio sets, meters, and other electrical
instruments.
• coefficient of friction (resistance to movement) of vulcanized rubber, which
is high on dry surfaces and low on wet surfaces, leads to the use of rubber
both for power-transmission belting and for water-lubricated bearings in
deep-well pumps.
• uncertainty of price and supply of natural rubber led to the development
of artificial