Topic 4 Materials

04/10/23 Topic 4: Materials 1

Design TechnologyTopic 4

Materials


4.1 Introducing and Classifying Materials


Classifying Materials

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.

3.1


Definitions

Atom - Molecule - Alloy - Composite -


Bonds

A bond as a force of attraction between atoms

Three main types of bond: Ionic (Crystalline Structure) Covalent (Shared electrons) Metallic (Sea of Electrons)


Classification

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.



Timber Metals Ceramics Plastics

Textile fibres Food Composites

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)

3.1


4.2 Properties of Materials


Physical Properties

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.

3.2


Physical Properties

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.

3.2


Density

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

is required.

3.2


Electrical Resistivity

Electrical resistivity is an important

consideration in selecting particular

materials as conductors or insulators for

particular design contexts.

3.2


Thermal Conductivity

Thermal conductivity is an important

consideration for objects which will be

heated, which must conduct heat or which

must insulate against heat.

3.2


Thermal Expansion

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.

3.2


Hardness

Hardness is an important consideration

where resistance to penetration or

scratching is required. Ceramic floor tiles are

extremely hard and resistant to scratching.

3.2


Mechanical Properties

Tensile Strength - The ability of a material to

withstand pulling forces.

Stiffness - The ability of a product to withstand bending.

3.2


Mechanical Properties

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)

3.2


Tensile Strength

The tensile strength of ropes and cables is an important safety consideration in climbing and in elevators.

3.2


Stiffness

Stiffness is an important consideration when maintaining shape is crucial to the performance of an object for example an aeroplane wing.

3.2


Toughness

Toughness is an important consideration where abrasion and cutting may take place

3.2


Ductility

Ductility is an important consideration when metals are extruded (do not confuse this with malleability—the ability to be shaped plastically).

3.2


Aesthetic Characteristics

Characteristics of taste, smell, appearance, texture and color

In what design context might these characteristics be important?

3.2


Aesthetic Characteristics

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

3.2


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.

3.3

04/10/23 Topic 4: Materials 263.3


Timber

4.3


Timber

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)


Timber

Normally Classified in two ways

Softwood (coniferous) Hardwood (deciduous)


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 CO2 percentages and less soil erosion.

Extinction of species is becoming a problem Removal of large stands often results in soil erosion


Composite Timbers

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

Composition Hardness Tensile Strength 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.


Seasoning

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 Finishing

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? Consider durability ease of maintenance aesthetics


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.

Alternative Assignment- Design a device that will carry 4 ice cream cones of

the different types available. A prototype is required.


Metals

4.4


Metallic Bonds

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)


Grains

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

plastic deformation - metals work-harden after being plastically

deformed.


Alloys

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.


Superalloys

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.

Wikipedia


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

Fe2O3 with SiO2 impurities) Has been extracted in blast furnaces since

the industrial revolution using limestone (CaCo3) and Coke (C)


Iron Ore

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) + Fe2O3 (s) → 2Fe (L) + 3CO2 (g)

Calcium oxide (CaO) from the limestone (CaCO3) is needed to remove the impurity silicon dioxide (SiO2) by combining with it to form slag (CaSiO3) via the reactions:

CaCO3 (s) → CaO (s) + CO2 (g)

CaO (s) + SiO2 (s) → CaSiO3 (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.


Wrought Iron

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.

Click Here


Further Processing

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


Alloys

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

US Steel Techno 2100 Metal Hardening How its Made Steel How its Made Steel Forging


Plastics

4-5


Covalent Bonds

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).


Secondary Bonds

weak (normally) forces of attraction between molecules

The number and type of secondary bonds will define the properties of the plastic


Thermoplastic Structure

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

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

Polyurethane*

Phenol formaldehyde (bakelite)

Urea-formaldehyde*

Other formaldehyde synthetics like, Formica, plywood resin, and super glue


Plastic Recycling

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


Ceramics (glass)

Glass is normally composed of;

70 % Silicon Dioxide (SiO2)

15 % Sodium Oxide (Na2O)

9 % Calcium Oxide (CaO)


Raw Materials

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 CaCO3) 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


Recycling

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


Energy Consumption

Ionic bonds in the raw materials require extremely high temperatures to break

The melting point of sand is approximately 2000K (31000F)

The addition of Soda Ash actually decreases the melting point somewhat

See Saint-Gobain Containers: Our Glassmaking Process


Properties of Glass

Extremely Hard Brittle Transparent Non reactive 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% SiO2, 10–25% B2O3, 2–10% Na2O

and 1–4% Al2O3).


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

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


Nylon

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.


Comparison

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.


Comparison continued

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 Finishing

Cotton normally requires finishing Must be dyed for colored uses Often waterproofed by applying a wax or oil


Nylon finishing

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


Composite Fabrics

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.


Manufacturing Processes

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.


Composites

4.7


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.

Fiber - 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

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

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


SMA Applications

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.


The End

Topic 4

Materials

Topic 4 Materials

Technology

Transcript of Topic 4 Materials