Materials can be classified into groups according to similarities in their microstructures and properties.
Several classifications are recognized but no single classification is “perfect”.
It is convenient to be able to classify materials into categories which have characteristic combinations of properties.
A bond as a force of attraction between atoms
Three main types of bond:
Ionic (Crystalline Structure)
Covalent (Shared electrons)
Metallic (Sea of Electrons)
Materials are classified into groups according to similarities in their microstructures and properties
Several classifications are recognized but that no single classification is "perfect“
It is convenient to be able to classify materials into categories (albeit crude in nature) that have characteristic combinations of properties.
For this course, materials are classified into groups: some of these groups have subdivisions 3.1
In each group there can be subdivisions
timber (natural wood or composite),
metals (ferrous or nonferrous),
ceramics (earthenware, porcelain and stoneware),
plastics ( thermoplastics or thermosets ),
Textile fibres (natural or synthetic),
food (vegetable or animal origin)
4.2 Properties of Materials
Density - The mass per unit volume of a material.
Electrical Resistivity - This is a measure of a material’s ability to conduct electricity. A material with a low resistivity will conduct electricity well.
Thermal Conductivity - A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab.
Thermal Expansion - A measure of the degree of increase in dimensions when an object is heated. This can be measured by an increase in length, area or volume. The expansivity can be measured as the fractional increase in dimension per Kelvin increase in temperature.
Hardness - The resistance a material offers to penetration or scratching.
Density is an important consideration in
relation to product weight and size (e.g. for
portability). Pre-packaged food is sold by
weight/volume and a particular consistency
Electrical resistivity is an important
consideration in selecting particular
materials as conductors or insulators for
particular design contexts.
Thermal conductivity is an important
consideration for objects which will be
heated, which must conduct heat or which
must insulate against heat.
Thermal expansion (expansivity) is an
important consideration where two dissimilar
materials are joined, such as glazed metals.
These may then experience large
temperature changes while staying joined.
Hardness is an important consideration
where resistance to penetration or
scratching is required. Ceramic floor tiles are
extremely hard and resistant to scratching.
Tensile Strength - The ability of a material to withstand pulling forces.
Stiffness - The ability of a product to withstand bending.
Ductility - The ability of a material to be drawn or extruded into a wire or other extended shape.
Toughness - The ability of a material to resist the propagation of cracks.
(Tough guys don’t crack)
The tensile strength of ropes and cables is an important safety consideration in climbing and in elevators.
Stiffness is an important consideration when maintaining shape is crucial to the performance of an object for example an aeroplane wing.
Toughness is an important consideration where abrasion and cutting may take place
Ductility is an important consideration when metals are extruded (do not confuse this with malleability—the ability to be shaped plastically).
Characteristics of taste, smell, appearance, texture and color
In what design context might these characteristics be important?
Some of the properties are relevant to only one materials group eg. food, while others can be applied to more than one. Although these properties activate peoples’ senses, responses to them vary from one individual to another and they are difficult to quantify scientifically, unlike the other properties
The IB Materials Matrix
It is possible to organize these groups and sub groups into a relatively easy to use matrix. (no longer required, but a good source)
The matrix gives an overview of the properties for each group.
Natural timber is a natural composite material comprising cellulose fibres in a lignin matrix.
The tensile strength of timber is greater along the grain (fibre) than across the grain (matrix)
Normally Classified in two ways
Softwood (Coniferous) Timber
Forests are located in earth’s Temperate zones
gymnosperms; the term gymnosperm is Latin for naked seeds.
typically have waxy, needle-like leaves that stay on the tree year round
The lumber produced from softwoods has no vessels or pores so the density or the wood is much more uniform
Hardwood (Deciduous) Forests
Located in Temperate and Tropical zones
Hardwoods are angiosperms
broad leaves that are usually lost in the winter
Seeds normally enclosed in some type of fruit or nut
The end grain of a hardwood contains pores
Forest area is declining
Timber is a renewable resource (?) only if reforestation is practiced.
Crop rotation cycles are normally in decades but sometimes in centuries.
Can employ different types of cutting practices to simulate natural phenomenon.
Areas with healthy forests experience lower CO 2 percentages and less soil erosion.
Extinction of species is becoming a problem
Removal of large stands often results in soil erosion
Plywood and Particle (Chip) Board are considered to be composite timbers.
These materials are made out of timber, but laminated or glued together to make the final product
Click here for how plywood is made
Click here for wikipedia chipboard
Pine vs. Composites
Compare the following properties for Mahogany, pine, plywood, and chip board
Resistance to Moisture
Aesthetics (color, texture, appearance of grain)
The ability to produce sketches showing cross-sectional views of the structure of the materials is expected.
Natural timbers require seasoning before use.
The IB defines seasoning as the process of drying out timber after conversion.
If wood is not allowed to season, bad things can happen.
Years ago, lumber was seasoned prior to cutting. Now lumber is typically wet cut and allowed to season after cutting.
Wood can be finished with a variety of substances to :
Prevent water absorption
Prevent attack by organisms or chemicals
Improve or change appearance
Modify other properties
What type of wood for a floor?
ease of maintenance
Build a Childs Toy
Design a toy for a child between the ages of 11 months and 5 years. Justify the materials that you use. This project will be graded in all criteria at IB standards.
Design a device that will carry 4 ice cream cones of the different types available. A prototype is required.
Metals are often described as positively charged nuclei in a sea of electrons. The outer electrons of the metal atom nuclei are free and can flow through the crystalline structure. The bonding is caused by attraction between the positively charged metallic atom nuclei and the negatively charged cloud of free electrons.
Properties of Metals
the movement of free electrons makes metals very good electrical and thermal conductors.
metals (pure or alloyed) exist as crystals.
Crystals are regular arrangements of particles (atoms, ions or molecules).
You should be able to draw and describe what is meant by grain size. (more info to come)
grain size can be controlled and modified by the rate of cooling of the molten metal, or by heat treatment after solidification.
Reheating a solid metal or alloy allows material to diffuse between neighboring grains and the grain structure to change. Slow cooling allows larger grains to form; rapid cooling produces smaller grains. Directional properties in the structure may be achieved by selectively cooling one area of the solid.
Smaller grain means harder material (but more brittle)
plastic deformation -
metals work-harden after being plastically deformed.
the tensile strength of a metal is increased by alloying (due to the internal structure with different sized atoms)
The presence of "foreign" atoms in the crystalline structure of the metal interferes with the movement of atoms in the structure during plastic deformation. This means that the alloy will be less malleable or ductile than the parent metals.
Great creep and oxidation resistance
Superalloys can be based on iron, cobalt or nickel. Nickel-based superalloys are particularly resistant to temperature and are appropriate materials for use in aircraft engines and other applications that require high performance at high temperatures, for example, rocket engines, chemical plants.
Iron (Fe) (this if for your info only)
Very reactive element that is never naturally found “free”
Makes up 5% of the earth’s core
Found as an ore (mainly haematite which is Fe 2 O 3 with SiO 2 impurities)
Has been extracted in blast furnaces since the industrial revolution using limestone (CaCo 3 ) and Coke (C)
Rich deposits are found in Russia, Brazil, Australia, and China.
After smelting, needs to be treated so that it does not react with air (moisture and water) and revert back to its oxide
The Chemical Process
Carbon monoxide (CO) from the carbon (C) is used to reduce the iron oxide to iron metal via the reaction:
3CO (g) + Fe 2 O 3 (s) -> 2Fe (L) + 3CO 2 (g)
Calcium oxide (CaO) from the limestone (CaCO 3 ) is needed to remove the impurity silicon dioxide (SiO 2 ) by combining with it to form slag (CaSiO 3 ) via the reactions:
CaCO 3 (s) -> CaO (s) + CO 2 (g)
CaO (s) + SiO 2 (s) -> CaSiO 3 (L)
The initial product
The iron produced in a blast furnace is an alloy called pig iron which, due to its high carbon (C) content (up to 4%), is very hard and brittle. Pig iron is not much use as an engineering material.
By melting the pig iron and reintroducing some slag, the carbon content of the iron is reduced (<0.3%)
Hammering hot slabs of this substance produces wrought iron which is more malleable and of higher tensile strength than the pig iron.
While wrought iron is suitable for many purposes, a stronger, tougher metal was still desired.
By reducing the carbon content even more, we can produce steel.
The carbon is reduced by blowing oxygen through the molten metal, where it bonds with the carbon to produce carbon dioxide gas
Steel in its basic form is an alloy of iron and carbon.
The more carbon the steel has, the harder, but more brittle it becomes.
Mild steel (very low carbon) is easily stamped into shape (car bodies for example)
Higher Carbon steel can be used for items like knives and bolts.
The troubles with Carbon Steel
It rusts when exposed to oxygen (produces Iron Oxide)
To prevent this, we need to coat it with a non - porous material.
Possibilities are: painting, electroplating with a different metal, or dipping it in molten zinc ( galvanizing )
Introducing other metals into the alloy
Steel can be formulated for specific properties by adding other substances into the alloy.
Adding Chromium (Cr) and Nickel (Ni) produces Stainless Steel which has fantastic resistance to rust and is non reactive with many chemicals.
Stainless is great for cutlery, or environments that are environmentally harsh due to its low upkeep requirement.
Steel Making videos
How its Made Steel
How its Made Steel Forging
In a covalent bond the outer electrons of some atoms come close enough to overlap and are shared between the nuclei, forming a covalent bond. Each pair of electrons is called a covalent bond. Covalent bonds are strong bonds and examples of primary bonds (as are metallic and ionic bonds).
weak (normally) forces of attraction between molecules
The number and type of secondary bonds will define the properties of the plastic
Thermoplastics are linear chain molecules, sometimes with side bonding of the molecules, but with weak, secondary bonding between the chains. Types of plastics
Think of this as a plate of spaghetti noodles
Stress (load) on Thermoplastics
Deformation occurs in two ways: elastic in which initially coiled chains are stretched ( no permanent deformation) and
plastic at higher loads, where secondary bonds weaken and allow the molecular chains to slide over each other (permanent deformation present).
Stress causes two types of deformation; creep and flow
Creep in Thermoplastics
Creep is the plastic deformation of a material that is subjected to a stress below its yield stress when that material is at a high homologous temperature. Homologous temperature refers to the ratio of a materials temperature to its melting temperature. The homologous temperatures involved in creep processes are greater than 1/3.
Flow in Thermoplastics
Continued stress or heat application will cause secondary bonds to break further, causing the plastic to become fluid.
This state is required for injection or blow mold processes
Effects are reversible in Thermoplastics
In Thermoplastics, heat or stress induced creep and flow are reversible
The plastic regains its secondary bonds and internal structure, albeit in a different shape than previously
Stated differently, the plastic will retain its new shape after plastic deformation, and retain its original properties
This makes thermoplastics ideal for recycling
Thermosets are formed by making primary (covalent) bonds which form strong, primary cross-links between adjacent polymer chains. This gives the thermoset a rigid three-dimensional structure.
Adding Heat to Thermosets
Unlike thermoplastics, when heat is added to the thermoset, the internal covalent bonding actually becomes stronger. This means that the thermoset will not plastically deform
Thermosets do not creep or flow.
Types of Thermoplastics
Polypropene * ( Polypropylene )
Polyethylene * ( PETE )
Polyvinyl Chloride ( PVC )
Types of Thermosets
Phenol formaldehyde ( bakelite )
Other formaldehyde synthetics like, Formica, plywood resin, and super glue
Thermoplastics can be easily recycled …why?
Thermosets are difficult to impossible to recycle…why?
What about PVC? click here
Product Design Using Plastics
In what context would you use thermoplastic in design?
What about thermosets?
Ceramics Section 4.6
Glass is normally composed of;
70 % Silicon Dioxide (SiO 2 )
15 % Sodium Oxide (Na 2 O)
9 % Calcium Oxide (CaO)
Sand granules are granules of Silicon Dioxide
Soda ash, either refined or from the mineral Trona provides the Sodium Oxide ( Sodium Carbonate)
Limestone (Calcium Carbonate CaCO 3 ) provides the raw ingredient for Calcium Oxide
Glass Requires large amounts of energy for manufacture, scrap glass is added to make the process more economical
Unlike some other materials, glass can be recycled an infinite number of times
Glass to be used for recycling (often waste from the previous process is called cullet
15 to 30 percent of scrap glass is used with raw materials during production
Ionic bonds in the raw materials require extremely high temperatures to break
The melting point of sand is approximately 2000K (3100 0 F)
The addition of Soda Ash actually decreases the melting point somewhat
See Saint-Gobain Containers: Our Glassmaking Process
Properties of Glass
Additions of different compounds can make for interesting aesthetic properties
Altering the properties of glass
Ordinary glass, also called “Soda Glass”, has poor “thermal shock” resistance.
If Boron Oxide and a small amount of Aluminum Oxide is used instead of the calcium Oxide, the glass produced can be very resistant to heat shock. This type of glass has the trade name Pyrex.
For information only, Pyrex is composed of
60–80% SiO 2 , 10–25% B 2 O 3 , 2–10% Na 2 O and 1–4% Al 2 O 3 ).
Altering the properties of glass
Toughened Glass is produced by reheating the glass to nearly its melting point, then allowing the surfaces to cool relatively quickly in relation to the internal glass.
This produces glass that shatters into small fragments when broken (automotive windscreens)
Altering the properties of glass
Laminated glass uses multiple panes of glass, often separated by a thin material (usually transparent plastic)
This type of glass is more difficult to break because of the properties of the insert.
When glass is both toughened and laminated, it is known as safety glass.
(glass can also be pored around a mesh of other materials like wire to make it stronger)
Glass as a structural material
plate glass and glass bricks are used as wall and flooring materials.
material properties, for example, resistance to tensile and compressive forces, thermal conductivity and transparency offer design considerations
There are numerous aesthetic properties and psychological benefits: glass allows natural light into buildings and can visually link spaces, creating more interesting interiors.
Textile Fibers Additional Information
Cotton grows in warm sub tropical climates and is mostly grown in the U.S., the Soviet Union, the Peoples Republic of China, and India. Other leading cotton growing countries are Brazil, Pakistan, and Turkey.
In this country the major cotton producing states are Alabama, Arizona, Arkansas, California, Georgia, Louisiana, Mississippi, Missouri, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas.
A natural fiber
Cotton is obtained from the bud of the cotton plant.
The cotton is harvested , cleaned, combed, and then spun into thread.
Cotton is a natural polymer composed of cellulose
Synthetic polyamide fiber made from Adipic acid and a diamine
Click here for a molecular picture
The two ingredients (in solution) are mixed, and the nylon fiber extracted, then spun into thread.
Cotton absorbs water, nylon does not (cotton actually becomes stronger when wet)
Nylon is elastic, cotton is not (means that it wrinkles and creases easily)
Nylon melts, then burns, while cotton tends to char only while exposed to flame.
Both products are degraded by ultraviolet light, but cotton slightly more
Cotton fibers breakdown with repeated exposure to moisture and air pollution
Cotton is susceptible to microbes like molds, Nylon is not.
Cotton normally requires finishing
Must be dyed for colored uses
Often waterproofed by applying a wax or oil
No finishing is required for nylon, it is naturally water repellant, and is colored to specification during the manufacture process.
Other Textile fibers
Plants: Flax, Jute, sisal, hemp, rice, bamboo, as well as others
Animal: Wool, Cashmere, Mohair, Alpaca, and Silk
Synthetic: Polyesters, Acrylic, Lycra, Olefin, and Lurex
Two or more types of textile can be blended to form different properties.
Socks often are made of cotton for absorbency, and nylon for strength.
Olefin is often added to cotton in a tight weave to aid in water resistance.
Acetates are used to make items shine.
Different processes can effect the properties of the cloth as well.
Open or loose weaves will make a cotton or nylon product more springy.
Tight weaves will make the product more stiff, and more water repellant.
What are composites?
Composites are a combination of two or more materials that are bonded together to improve their mechanical, physical, chemical or electrical properties.
Wikipedia on strength and layout of fibers
New materials can be designed by enhancing the properties of traditional materials to develop new properties in the composite material.
Smart Materials have one or more properties that can be dramatically altered, for example, viscosity, volume, conductivity. The property that can be altered influences the application of the smart material.
Smart materials include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, and shape memory alloys. Some everyday items are already incorporating smart materials (coffee pots, cars, the International Space Station, eye-glasses), and the number of applications for them is growing steadily.
Piezoelectric materials can be used to measure the force of an impact, for example, in the airbag sensor on a car. The material senses the force of an impact on the car and sends an electric charge to activate the airbag.
electro-rheostatic and magneto-rheostatic materials.
Electro-rheostatic (ER) and magneto-rheostatic (MR) materials are fluids that can undergo dramatic changes in their viscosity. They can change from a thick fluid to a solid in a fraction of a second when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the field is removed.
MR and ER Fluids
MR fluids are being developed for use in car shock absorbers, damping washing machine vibration, prosthetic limbs, exercise equipment, and surface polishing of machine parts.
ER fluids have mainly been developed for use in clutches and valves, as well as engine mounts designed to reduce noise and vibration in vehicles
shape memory alloys (SMAs )
SMAs are metals that exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material. Pseudo-elasticity occurs without a change in temperature. The load on the SMA causes molecular rearrangement, which reverses when the load is decreased and the material springs back to its original shape. The shape memory effect allows severe deformation of a material, which can then be returned to its original shape by heating it. Click
Applications for pseudo-elasticity include eye-glasses frames, medical tools and antennas for mobile phones. One application of shape memory effect is for robotic limbs (hands, arms and legs). It is difficult to replicate even simple movements of the human body, for example, the gripping force required to handle different objects (eggs, pens, tools). SMAs are strong and compact and can be used to create smooth lifelike movements. Computer control of timing and size of an electric current running through the SMA can control the movement of an artificial joint. Other design challenges for artificial joints include development of computer software to control artificial muscle systems, being able to create large enough movements and replicating the speed and accuracy of human reflexes.