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AQA A Level product Design (Technical principles)
Terms in this set (48)
Mechanical Properties (m)
associated with how a material reacts to an external force
physical properties (P)
associated with the actual make-up or structure of the material
compressive strength (Mechanical)
the ability to withstand being crushed or shortened by pushing forces (compression)
tensile strength (mechanical)
the ability to resist stretching or pulling forces (tension)
Bending strength (mechanical)
the ability to resist forces that may bend the material
shear strength (m)
the ability to resist sliding forces on a parallel plane
Torsional strength (m)
the ability to withstand twisting forces from applied torque or torsion
the ability to resist abrasive wear such as scratching, surface indentation or cutting
the ability to absorb impact force without fracture
the ability to be permanently deformed (shaped) and retain the deformed shape
the ability to be drawn out under tension, reducing the cross-sectional area without cracking, for example stretching a material into a wire
the ability to withstand deformation by compression without cracking. Malleability increases with a rise in temperature
the ability to be deformed and then return to the original shape when the force is removed
Electrical conductor (p)
allows the flow of electrical current through the material. A good conductor gives very little resistance to the flow of change.
An electrical property.
electrical insulator (p)
does not allow the flow of electricity through the material
An electrical property.
Thermal conductor (p)
allows the transfer of heat energy through the material. A material with high thermal conductivity allows the transfer of heat to occur quickly across the material
A thermal property
thermal insulator (p)
prevents the transfer of heat through the material.
A thermal property
Thermal expansion (p)
the increase in material volume in response to the heat input.
A thermal property.
prevents light form travelling through
A optical property.
allows light through but diffuses the light so that objects appear blurred. Frosted glass is an example of it.
an optical property
allows light to pass through easily which means you can see clearly through the material
An optical property
the mass of a material in a standard volume place
the ability of the material to be fused or converted from a solid to a liquid or molten state, usually by heat. It is an essential property for a metal being cast
the natural force between objects that causes the material to attracts iron or steels
Corrosion/degradation resistance (p)
The ability of the material to withstand environmental attack and decay.
- a metal containing iron and carbon
- are magnetic and will rust
e.g. Low carbon steel
- a metal that does not contain iron
- not magnetic and do not rust
- A metal containing 2 or more metals, or combining 2 or more elements, one of which must be a metal
- can also be sub classified as ferrous alloys or non-ferrous alloys
e.g. stainless steel
the wood from broad-leaved, mostly deciduous trees
These trees are generally slow growing and lose their leaves in Autumn
A wood from a coniferous tree
these trees are fast growing and tend to be evergreen
a man-made, wood-based composite material.
Available in much larger sizes than solid wood
a material which can be repeatedly reheated and reshaped, allowing it to be recycled after its initial use
They have long linear chain molecules held by van der Walls forces
e.g. Low Density Polyethylene (LDPE)
a material which when heated undergoes a chemical change whereby the molecules form rigid cross-links. Cannot be reheated or reshaped, even at very high temperatures.
e.g polyester resin
a material which at room temperature can be deformed under pressure and then upon release of the pressure, will return to its original shape
They have weak bonds which allow them to stretch easily. They can be stretched repeatedly and upon immediate release of the stretch, will return with force to the original length
e.g. Natural rubber
Papers and boards
can be described as compliant materials, meaning they can be scored, folded and cut with basic tooling to form items such as nets for packaging
e.g. Layout paper
being made of 2 or more substances creating unique characteristics and properties when combine
- can be fibre based
- can be particle based
- can be sheet based
Materials which change in response to their surroundings, such as light levels or temperature.
e.g. shape memory alloys (SMA)
a material developed through the invention of new or improved processes e.g. a result of man-made materials or human invention
They are not smart materials
Testing - tensile strength
- The ability to resist stretching or pulling forces
- This can be tested in a workshop by clamping material samples of the same length and thickness into a vice and applying a load such as weights to the unclamped end
- It is how much impact force the material can absorb
- Material samples are clamped into a vice. Each sample then hit with the same force, using a hammer
- Tough materials absorb the impact. Brittle materials bend or shatter
Hardness testing - Abrasive wear
- running a file over the surface of the material, using the same force for each material.
- The material with the least scratches is the hardest
Hardness testing - resistance to surface indentation
- The material is fully supported underneath and the dot punch is placed onto the material surface. The dot punch is hit once with a hammer, using the same force for each sample. The smaller the indent, the harder the material
Malleability and ductility testing
- Secure the test piece into the vice. Try to bend the test piece 90 degrees. Cracks or surface damage on the outside of the bend indicates a lack of ductility. Cracks or surface damage on the inside of the bend indicates a lack of malleability
- all test pieces should be the same size. Materials can simply be placed outside in an area exposed to weather effects and left for a certain length of time. Materials can then be visually inspected for surface corrosion.
Conductivity testing - electrical
- collect material samples of the same dimensions and, on the top surface, mark a set distance between the ends of the material sample. The distance is the spacing for each probe of the multimeter. Place the probes on the distance marks and measure the resistance on the multimeter. The higher the resistance, the lower the conductivity
Conductivity testing - Thermal
- Collect material samples of the same dimensions. Measure a set distance from one end of the material on which to place a thermometer. A bunsen burner is lit to reach a set point at the other end of the material sample. The shortest time it takes to reach the set temp, the higher the thermal conductivity
Industrial testing - Tensile testing
- a standard test piece is placed into a tensometer machine and held in clamps at each end. one clamp is fixed and the other moves on a worm drive gear mechanism. As the worm drive travels at a constant rate, the test piece is put under tension. As the test piece is stretched, the load and distance travelled is plotted, giving information on elastic limit, yield point maximum load and final breaking point from 'necking'
Industrial testing - toughness
The Izod impact test is used to test the toughness of a material. A notched test piece is held vertically in the vice of a test machine. A pendulum is released from a set position and swings to strike a test piece. The energy absorbed by the test piece is calculated from the height the pendulum swings to after it hits the test piece. The material that absorbs the most impact is the toughest. This is shown the distance the pendulum travels after breaking the material. The further it swings, the less energy the sample absorbs and the more brittle the material
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