UNIT 2 - PERFORMANCE CHARACTERISTICS

Question 1

ELECTRICAL CONDUCTOR

Answer 1

• allows the flow of electrical current through the material

- a good conductor gives very little resistance to the flow of charge

Question 2

ELECTRICAL INSULATOR

Answer 2

• does not allow the flow of electricity through the material

Question 3

THERMAL CONDUCTOR

Answer 3

• 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

Question 4

THERMAL INSULATOR

Answer 4

• prevents the transfer of heat through the material

Question 5

BENDING STRENGTH

Answer 5

• ability to resist forces that may bend the material

Question 6

COMPRESSIVE STRENGTH

Answer 6

• ability to withstand being crushed or shortened by pushing forces

Question 7

TENSILE STRENGTH

Answer 7

• ability to resist stretching or pulling forces

Question 8

SHEAR STRENGTH

Answer 8

• ability to resist sliding forces on a parallel plane

Question 9

TORSIONAL STRENGTH

Answer 9

• ability to withstand twisting forces from applied torque or torsion

Question 10

ELASTICITY

Answer 10

• ability to be deformed and then return to the original

shape when the force is removed

Question 11

PLASTICITY

Answer 11

• ability to be permanently deformed (shaped) and retain the deformed shape

Question 12

MALLEABILITY

Answer 12

• ability to withstand deformation by compression without cracking
• malleability increases with a rise in temperature

Question 13

DUCTILITY

Answer 13

• ability to be drawn out under tension, reducing the cross-sectional area without cracking, for example, stretching material into a wire

Question 14

HARDNESS

Answer 14

• ability to resist abrasive wear such as scratching, surface indentation or cutting

Question 15

TOUGHNESS

Answer 15

• ability to absorb impact force without fracture

Question 16

DURABILITY

Answer 16

• ability to withstand general wear over a period of time

Question 17

BIODEGRADABILITY

Answer 17

• ability to naturally decompose by the actions of bacteria or other living organisms

Question 18

WOODS

Answer 18

• wood fibres grow along the length of the tree or branch (grain)
• cut wood can expand/shrink depending on humidity
• after being cut, wood is seasoned (air or kiln) to remove excess moisture (80-90%) before use
• seasoning wood helps to prevent defects such as twisting, warping, cracks, cupping or bowing
• strong in the direction of the grain and weaker across the grain
• natural material and will biodegrade if left in landfill

Question 19

METALS

Answer 19

• naturally occurring material and is mined from the ground in the form of ore
• approx 25% of earth’s crust is made up of metal ores
• bauxite - aluminium’s ore - most common
• raw metal is extracted from the ore through crushing, smelting or heating, with the addition of chemicals and huge amounts of electrical energy

Question 20

POLYMERS

Answer 20

• most polymers are made via the fractional distillation of crude oil (non-renewable source)
• polymers made from crude oil take hundreds of years to degrade
• polymers are ‘self-finishing’ - can be pigmented during the manufacture process to give colour and therefore require no finishing process

Question 21

SMART AND MODERN MATERIALS

Answer 21

• smart materials - physical properties change in response to an input or change in environment, such as temp, electricity, pressure or light
• modern materials are developed through the invention of new or improved processes and will continue to be created as technology advances
• common smart material = thermochromic material - responds to a change in temperature

Question 22

PAPERS AND BOARDS

Answer 22

• can be scored, folded and cut with basic tooling to form items such as a net for packaging
• original source of paper is wood pulp
• during manufacture, bleaches are often added to make the paper or board whiter
• come from a natural source
• suitable for recycling and will naturally biodegrade

Question 23

TEXTILES

Answer 23

• natural fibres - plant based like linen and cotton or animal based like wool
• natural fibres are naturally reoccurring, can be recycled and will biodegrade
• manmadde fibres are not naturally occurring - theyre synthetic and have been developed in a lab
• textiles can be made flame resistant and stain resistant

Question 24

COMPOSITES

Answer 24

• material with enhanced properties
• most common composites - carbon fibre reinforced polymer (CRFP) and glass reinforced fibre (GRP)
• GRP and CRFP have many useful properties - lightweight, corrosion resistant, tough, hard, low thermal expansion, easily moulded into 3D forms
• also include wood composite boards such as MDF, hardboard, chipboard, plywood - no natural defects such as splits and knots and boards come in large sheets