Unit 6 - Materials And Their Properties Flashcards
Name some physical properties
Elasticity
Density
Hardness
Toughness
Brittleness
Malleability
Conductivity
What is the density formula
Density = mass X volume
What is ‘melting point’
A phase change where the substance goes from solid to a liquid where they exist in equilibrium
What is specific heat capacity
The ratio of the amount of energy transferred to a material and the change in temperature
What is the specific heat capacity formula
C=Q / deltaT
delta is a triangle and means change
T represents temperature
C is Celsius
Q is energy. (joules, J)
What is temperature usually expressed in
Celsius (C) or kelvins (k)
What is thermal expansion
A fractional change in the size of a material in response to a change in temperature
What are examples of thermal expansion
Changes in original length (linear expansion)
Changes in area ( areal or superficial expansion)
Changes in volume(volumetric or cubical expansion)
What is the thermal expansion formula
Change in length= original length-container of material- change in time
What is the meaning of permittivity
Measure of how a material distorts at atomic level when in an electric field
What are physical properties
Properties that are measureable
What are mechanical properties
How a material performs when different forces are applied to it. Eg strength ,ductility and wear resistance
What is fatigue strength
Refers to the maximum stress that a material can withstand in a given number of cycles
What is shear strength
Directional forces cause the internal structure of a material to slide against itself at the granular level
What is tensile strength
Amount of load a section of a material can withstand before it breaks
Usually measured in Newtons/mm or megapascals per square inch
What is yield strength
Describes the point after which a material under load will no longer return to its original shape or position
What is toughness
Represents a materials ability to absorb impact without fracture at a given temperature
Often measured using the charpy impact test
What is hardness
Defined as a materials ability to resist permanent indentation
What is ductility
Capacity to deform under stress
What is plasticity
How far an object can be stretched
What is a materials strength
Ability to withstand force without deformation or damage
What is ferrous metals
Metals that contain iron eg steel and iron
What are non-ferrous metals
Metals that don’t contain iron eg lead, tin, aluminium, copper, gold
What is an alloy
Mixture of 2 or more elements including at least one metal eg duralumin, steel, solder
What is wrought iron
100% iron
Properties: fibrous, tough, ductile, rust resistant
What is cast iron
94-98% iron , 2-6% carbon
Properties: strong but brittle, high compressive strength
What is stainless steel
Iron, nickel and chromium(% differs by grade)
Properties: tough, resistant to rust, subject to stains
What is carbon steel
Carbon 0.6-1.4% Iron 98.6-99.4%
Properties: tough, can be hardened and tempered
What is mild steel
Carbon ->0.1-0.3% iron 99.9-99.7%
Properties: tough, high tensile strength, can be hardened, rusts easily
Silicon ‘bronze’ alloy
Good corrosion resistance, particularly in sulphurous atmospheres and are used as access fittings for chimneys
Copper-aluminium alloys(‘bronzes’)
Bright golden-yellow, very strong and resistant to corrosion. Can be made soft and ductile
Delta bronze
An example of a wrought alloy as it contains about 1% aluminium, iron, nickel and manganese
What are thermoplastics
A resin solid at room temp but becomes soft plastic when heating crossing the glass transition temperature
Uses of thermoplastics
Injection moulding or blow moulding as set as shape of mould
Key advantage of thermoplastics
The reversibility of the process allows it to be used for more a different product at the end of its lifespan
Common thermoplastic materials
Polyethylene. PE
Polycarbonate. PC
Polyvinyl chloride. PVC
What are thermoset plastics
A harder and more rigid plastic than thermosetting which cannot be reheated. The polymers become cross linked together and cannot be broken
Examples of thermoset plastics
Urea-formaldehyde foam- used in plywood and mdf boards
Melamine resin-used on worktop surfaces
Diallyl-phthalate (DAP) - electrical connectors
Epoxy resin- fibre-reinforced plastics
Silicone resin- ceramic matrix composite
What are elastomers
A form of plastic with loosely cross linked polymers eg rubber
Properties of elastomers
Flexible and elastic ( can be stretched easy and return to original shape when force removed)
What are composites (Fibre-reinforced polymers)
A polymer matrix reinforced with fibre or other reinforcing materials. The matrix protects the fibres from external and environmental damage and the fibres strengthen and stiffen the matrix to resist cracks/fractures
Examples of composites
MDF- compressed wood fibres
Plywood- thin layers of wood bonded with grain ms at right angles
Glass reinforced plastic(GRP)- epoxy resin or polyester resin recorded with glass fibre matting
Carbon fibre reinforced plastic- epoxy or polyester resin backed with carbon fibres that are baked to set
How is GRP made
Make mould. Add roving to sprayed on fibre glass. Add deck
Strengths of composites
Weight
Weather resistance
Moulded into any shape
Lightweight
What is a polymer
A long chain of monomers as poly mean many in Greek
What is bending
A flexible metal forming process which uses brake press or a similar press method to press sheet metal over a die block into a shape.
It does not actually create a hole.
What is rolling
A process that reduces thickness of metal
What does hot rolling do to the material
Enhanced toughness and ductility and affects the shape as much larger than cold rolling
However it is susceptible to shrinkage
What is roll forming
A process that shapes metal as it passes through multiple sets of rollers. These continuously form and bend the sheets into desired shape.
What is cold working
A process where metal is hardened by plastic deformation at temperatures below recrystallision temperature.
What happens to the object when cold working is used
Internal and residual stresses build up in the metal which may lead to cracks. The metal has a high uniformity
What happens to the object in hot working
No internal stresses build up and it can remove cracks and faults. It is important in increasing the ductility of the metal
what is stretching
A form of metal processing where the workpiece is simultaneously bent and stretched over a die. It occurs through radial strain and is used for large parts
What is deep drawing
Common metal forming process that is where the sheet is clamped and placed over a cavity shaped due to form hollow components. The tensile strength applied to the sheet is deformed to the external shape of the part
What is sintering
Also called frittage. A process of forming a solid mass through heat, pressure but without liquefaction. It involves the atoms diffusing across the particle boundary and fusing
Positives of singering
Strength
Integrity
What is a smart material
Prosperities can change depending on the environment
What are piezoelectric crystals
Certain crystals such as quartz, when a force or pressure is applied causes a voltage to be set up. When reversed an a voltage is applied it can cause twists or bends in a controlled manner
What are SMA’s
Shape memory alloys are a combination or multiple metals which have been deformed as a result of heat or external forces. They return to the original or permanent shape when heated
What are QTC’s
A material that acts as an insulator in its normal state but under compression becomes a conductor
What are advantages of SMA’s
Diverse range of uses
Strength
Corrosion resistance
Ability to replace living tissue
High level of recoverable plastic straon
What are disadvantages of SMA’s
Expensive
Poor fatigue
Potential to over stress
Sensitivity to fabricated properties
Stress can build within thin films
Low maximum frequency
What are thermo ceramics
Materials produced by combining ceramics and metallic powders through sintering. The powders are heated then placed in a die under pressure until particles bond
Properties of thermo ceramics
Very hard and stable but brittle and breakable if dropped
What are the three categories of wood
Softwood, hardwood and engineered wood
What are engineered woods
Not natural but manufactured from waste wood to have certain wualities
What are hardwoods
From trees without needles or cones also known as deciduous trees. Trees that produce leaves and seeds. They are typically more expensive
What are softwoods
From wood and lumber which are milled from conifer trees which have needles and cones such as pine, cedar, spruce etc
How can you tell hardwood and softwoods apart
Softwood I’d evergreen trees which grow faster and are cheaper. They can be seen as different by the structure of their grain
What is hardboard
Engineered wood made from wood fibres mixed with steam and heat then compressed into boards. Used on the construction industry because of its strong and dense properties
What is plywood
Made of sheets of wood veneers called piles which are glued together. It is used to construct furniture, floors and walls. It is strong yet adaptable
What is chipwood
Made from small waste wood particles compressed and bonded with resin. It is an affordable yet sustainable choice
What are van der waals bonds
Appear most in plastics and polymers. They are long strong molecules consisting of carbon atom’s covalently bonded with other atoms.
They are very strong and take strong forces to rupture. The bonds between molecules that slide are called van der walls forces
What is a crystalline solid
A 3D pattern called a crystal lattice with uniform intermolecular forces
What is an amorphous solid
Shapeless , disordered and irregular arrangement of the particles of a solid. The intermolecular forces and distances between the particles are not the same
