Studied by 17 peopleTags & Description
Alloying
Alloys are a mixture that contains at least one metal.
Alloying increases strength and hardness
Alloying reduces malleability and ductility, of alloys compared to pure metals.
This is due to the presence of “foreign” atoms which interfere with the movements of atoms in the crystals during plastic deformation
Work hardening (Cold working or Strain Hardening)
Is the process of toughening the a metal through plastic deformation.
Tempering
Tempering is a heat treatment process
Usually carried out after hardening of a metal to:
increase its toughness and ductility
decrease hardness and brittleness
Superalloys
Exhibits excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion.
Creep
Creep is the tendency of a metal (or material) to slowly move or deform permanently due to the long term exposure of stress that are below the yield strength or ultimate strength of the metal.
Oxidation resistance
Oxidation is the interaction between oxygen and different substances when they make contact, such as rust Fe2O3
Oxidation resistance is the ability of a material to resist the direct and indirect attack of oxygen (oxidation) and degradation.
Ferrous Alloys
Mild Steel
Carbon content of 0.1 to 0.3% and Iron content of 99.7 – 99.9%. Used for engineering purposes and in general, none specialised metal products.
Ferrous Alloys
Stainless Steel
Made up of Iron, nickel and chromium. Resists staining and corrosion and is therefore used for the likes of cutlery and surgical instrumentation.
Ferrous Alloys
Cast Iron
Carbon 2 – 6% and Iron at 94 to 98%. Very strong but brittle. Used to manufacture items such as engine blocks and manhole covers.
Non-ferrous Alloys
Aluminum
An alloy of aluminum, copper, and manganese. Very lightweight and easily worked. Used in aircraft manufacture, window frames, and some kitchenware. Pure Aluminum can be used in drink cans.
Non-ferrous Alloys
Copper
Copper is a natural occurring substance. The fact that it conducts heat and electricity means that it is used for wiring, tubing and pipe work.
Non-ferrous Alloys
Brass
A combination of copper and zinc, usually in the proportions of 65% to 35% respectively. Is used for ornamental purposes and within electrical fittings.
Non-ferrous Alloys
Silver
Mainly a natural substance, but mixing with copper creates sterling silver. Used for decorative impact in jewellery and ornaments, and also to solder different metals together.
Non-ferrous Alloys
Lead
Lead is a naturally occurring substance. It is heavy and very soft and is often used in roofing, in batteries and to make pipes. (from CastleMetalsEurope)
Natural Timber
A natural composite material comprising cellulose fibres in a lignin matrix.
Seasoning
Seasoning is the commercial drying of timber which reduces the moisture content of wood.
Air-drying
Stacks of sawn timber in the open or in large sheds. There is little control over the drying process as the weather elements have affects.
Kiln-drying
Stacks of sawn timber in a kiln, to reduce the moisture content in wood, where the heat, air circulation, and humidity is closely controlled.
Timber Defects
Warping
Distortion in wood caused by uneven drying, which results in the material bending or twisting.
Timber Defects
Bowing
Is the warping along the length of the face of the wood.
Timber Defects
Cupping
Warping across the width of the face of wood, in which the edges are higher or lower than the center.
Timber Defects
Twisting
Warping where the two ends of a material do not lie on the same plane.
Timber Defects
Knots
Imperfections in timber, caused by the growth of branches in the tree that reduces its strength.
Natural Timber
Is timber that is sawn from the tree and is used as is (ie not made into plywood, etc). This includes hardwood and softwood trees.
Characteristics of natural timber
Tensile Strength: The tensile strength of natural timber is greater along the grain than across the grain.
Resistance to damp environments: is very resistant.
Longevity: Hardwoods very good. Softwoods good.
Aesthetic properties: natural colours range (red, purple, cream and brown). The grain can add to its aesthetics.
Man-made timbers
Plywood
(very thin slices of wood) glued together perpendicularly.
Man-made timbers
Particle board (Chipboard)
Made from different sizes of wood chips, joined with glue and pressed.
Man-made timbers
MDF (Medium Density Fibre Board)
Strands of fibre ruled together and pressed into sheets.
Lamination
Covering the surface with a thin sheet of another material (plastic laminate, wood veneer, etc) typically for protection, preservation or aesthetic reasons.
Characteristics of man-made timber
Tensile strength: depends on the man-made timber
Plywood – high tensile strength in all directions
Particle board and MDF – very low
Resistance to damp environments: depends on the man-made timber.
Exterior plywood – excellent.
Interior plywoods very low
Particle board and MDF – very low
Longevity:
Plywood is high
Particle board and MDF is low to medium
Aesthetic properties:
Plywood if the top layer is of a nice timber like Beech will be good
Particle board and MDF requires finishing or a sheet of lamination (see previous section)
Creosote
A material that penetrates the timber fibres protecting the integrity of the wood from attack from borer, wood lice and fungal attack.
Reasons for Treating and finishing timbers
Reducing attack by insects, fungus and marine borers by making the wood poisonous
Creosote: A material that penetrates the timber fibers protecting the integrity of the wood from attack from borer, wood lice and fungal attack.
Protection from the weather
Protection from Dry rot.
Where timber is subjected to decay and attack by fungus.
Improving chemical resistance
Enhancing aesthetic properties
Modifying other properties
Glass
Glass is primarily composed of silca sand (silicon dioxide) together with limestone (calcium carbonate) and Soda Ash (sodium carbonate) and small quantities of a few other chemicals.
Characteristics of glass
Transparency, allows light to pass through thus allowing you to see the contents of a jar or through a window.
Colour, colour can de deigned in my adding chemicals
Strength – low tensile strength but high compressive strength
Brittleness, it has a low impact strength and thus will shatter easily (low toughness).
Hardness, high hardness and wont scratch readily.
Un-reactivity – is chemically inert so leaching of acid based contents is not a problem.
Non-Toxic due to its un-reactivity therefore suitable for food storage.
Non-porous, thus will hold liquids or stop moisture seeping from outside.
Insulator.
100% recyclable and is continuously recyclable
Recycling of Glass
Recycled glass is known as cullet which is added to new raw materials to make new glass.
It reduces the energy required thus the costs in producing new glass.
When recycled the glass is separated into the same colours groups (due to chemical compounds) then are crushed .
Applications of glass
Soda Glass
This commercial glass and is the most commonly used. Has medium to low thermal shock, in other words it will shatter going from cold to hot or the other way.
Applications of glass
Borosilicate (Pyrex)
Commonly known as Pyrex. The chemical composition of Soda Glass is altered by the addition of oxides which improve thermal conductivity.
Applications of glass
Toughened
Is heated up to the point of melting then blasted with cold air. This makes the outside is in compression and the slower cool interior is in tension. When it is impacted it shatters into little pieces rather than sharp shards.
Applications of glass
Laminated
It is layers of glass and plastic sheets between them. When impacted, the glass fragments are held in place. This prevents cracks from growing
Application of glass
Glass Fibre
Is a very long strand of glass. Sometimes these are woven into mats and used as glass fiber reinforced plastic when combined with a resin (polymer).
Thermoplastics
Are linear chain molecules with weak secondary bonds between the chains.
General for thermoplastics characteristics include:
ductile
low stiffness – squishy water bottles for example
easily injected into a mould
can be reshaped after heating
easily and cost effectively manufactured
PP (Polypropene)
lowest density of thermoplastics
good toughness
resistant to fats
high resistance to temperature
good fatigue resistance
semi-rigid
translucent
recyclable
PE (Polyethene)
low stiffness (semi-rigid, flexible)
high toughness
translucent
commonly HDPE and LDPE
recyclable
PET (Polyethylene terephthalate)
high strength
rigid
thermal resistant
recyclable
ABS (Acrylonitrile butadiene styrene)
high impact resistance
high toughness
dimensional stability
good stiffness
good workability properties
versatile material
repayable – not all centres will receive it.
HIPS (High Impact PolyStyrene)
easy of fabrication
high impact strength
good aesthetics-various colours
rigid/stiff
low cost
dimensional stability
good workability properties
non-biodegradable
PVC (Polyvinyl chloride)
Can be stiff or flexible (when a plastizeer is added)
good aesthetics – colours
low cast
non-biodegradable
Type of thermoset:
Polyurethane
It can be hard like fibreglass or soft and spongy
wide range of hardness
good tensile and compressive strength
toughness – impact resistant
good electrical resistivity
good bonding properties
good resistant to damp environments
Type of thermoset:
Urea-formaldehyde
high (surface) hardness
high tensile strength
good
electrical resistivity
low resistance to damp environments
deterioration of indoor are quality
Type of thermoset:
Melamine resin
high hardness (one of the highest)
high chemical resistance resin
medium fire and heat resistant (will decompose under great heat)
resistant to moisture (damp environments)
Type of thermoset:
Epoxy resin
high thermal resistance
high chemical resistance
high toughness
Nearly all plastics can be recycled it mostly depends on economic, technical and logistical factors
Thermoplastics can be easily recycled.
come in a range of chemical compounds and therefore need to be sorted for recycling
Thermosets not so easy (and expensive to do so)
need to be ground into a powder which adds time and costs.
Often get sent to landfill
Natural fibres
Materials produced by plants or animals that can be spun into a thread, rope or filament.\
Common examples include:
Wool
Cotton
Silk
Synthetic fibres
Fibres made from a man-made material that are spun into a thread; the joining of monomers into polymers by the process of polymerisation.
Acrylic, nylon, polyester, lyrca, rayon, acetate, spandex, and Kevlar
Properties of natural fibres
Absorbency – is very high
Strength – low tensile strength
Elasticity – not very elastic
Effect of temperature – will burn but does not melt.
Properties of synthetic fibres
Absorbency – is very low
Strength – high tensile strength
Elasticity – highly elastic (like stockings, socks etc)
Effect of temperature – will burn and melt.
Conversion of yarns into fabrics:
Weaving
The act of forming a sheet like material by interlacing long threads passing in one direction with others at a right angle to them.
Conversion of yarns into fabrics:
Knitting
A method for converting a yarn into fabric by creating consecutive rows of interlocking loops of yarn.
Conversion of yarns into fabrics:
Lacemaking
A method for creating a decorative fabric that is woven into symmetrical patterns and figures.
Conversion of yarns into fabrics:
Felting
A method for converting yarn into fabric by matting the fibres together.
What is a composite?
A mixture composed of two or more materials with one acting as the matrix (glue) the other acts as a reinforcement (fibres/sheet/particles).
Composition and structure of composites
Concrete
Water, Portland cement, and aggregates (gravel etc)
Composite and structure of composites
Engineered wood
Also called composite wood, man-made wood, or manufactured board. gluing sheets (veneer), particles or stands of wood together.
Composite and structure of composites
Plywood
Sheets of venner glued together with the grain perpendicular to each sheet.
Composite and structure of composites
Particleboard
Chips of wood glued together (see above image).
Composite and structure of composites
Fibreglass
Stands of glass, formed into a matt and then covered in resin (polymer/thermoset plastic).
Composite and structure of composites
Kevlar
Para-aramid synthetic fiber covered in a resin
Composite and structure of composite
Carbon
Reinforced plastic – carbon fibres formed into a matt (see above image) then covered in resin.
Composite and structure of composite
Laminated veneer lumber (LVL)
Uses multiple layers of thin wood assembled with adhesives
Note
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