Unit 8

Question 1

Constraints (definition + types)

Answer 1

Effect of external forces on objects

Compression: crush
Tension: stretch
Torsion: twist
Deflection: bend
Shearing: cut

Question 2

Deformation (definition)

Answer 2

Constraints have a tendency to deform objects

Question 3

Types of deformation

Answer 3

Elastic: temporary change, constraint removed, returns to orignal shape
Plastic: permanent change in the shape or dimensions of the material
Fracture: material breaks

Question 4

Mechanical Properties

Answer 4

1. Hardness: Ability to resist indentation, abrasion (scratches) deformation
2. Elasticity: Ability to deform & return to its original shape after constraint removed
3. Plasticity: Doesn’t return to its original shape after stress, can be shaped
4. Resilience: Ability to resist shocks without breaking, often deform and return to original shape
5. Stiffness: Ability to retain shape when subjected to constraint (no bending though)
6. Toughness: Ability to absorb energy and plastically deform without fracturing (plastic)
7. Compressive strength: Resist compression
8. Tensile strength: Resist tension
9. Shearing strength: Resist shearing
10. Ductility: Manufacturing metals Stretching into wire without breaking
11. Malleability: Manufacturing metals Flattened into sheet or bent (shaped) without breaking

Question 5

Electro-chemical properties

Answer 5

1. Chemical neutrality: Ability to be chemically inactive; resist chemicals
2. Resistance to corrosion: Prevent formation of rust; resist effects of corrosive substances
3. Electrical conductivity: Ability to carry an electric current
4. Heat resistance or conductivity: Ability to resist or transmit heat
5. Lightness*: A property of low density materials

Question 6

Degradation

Answer 6

Decline in properties due to effects of environment

Question 7

Protection

Answer 7

Application procedures to prevent/delay degradation: protective coating

• Zinc coating (galvanization), anti-rust - metals
• Incorporating pigments and/or antioxidants - plastics
• Applying paint or varnish, waterproof coating - any materials

Question 8

Wood

Answer 8

Organic matter from trees
Deciduous: slow growth, hardwood
Coniferous: fast growth, softwood

• x conduction of heat and electricity
• needs to be treated (fungus, insects, water)

Question 9

Metals

Answer 9

Alloys
- Conductors of heat and electricity
- grease, paint, phosphate (prevent rust)

Question 10

Ceramics

Answer 10

Inorganic material (silicon dioxide SiO2)
- x conductor of heat and electricity
- hard (not resilient)
- stiff
- heat resistance
- corrosion resistance

• waterproof

Question 11

Thermoplastics

Answer 11

Soften and melt if heat applied
- X conductors of heat and electricity
- elastic
- light
- chemical neutrality
- corrosion resistance
- resilient

Question 12

Thermosets (Thermosetting plastics)

Answer 12

Once formed, doesn’t soften or melt when heat applied
- x conductors of heat and electricity
- hard
- stiff
- heat resistant
- corrosion resistant
- resilient

Question 13

Links

Answer 13

Direct vs Indirect: Does it have something that helps connect to?
Rigid vs Flexible: Solid or bendable?
Removable or Non-Removable: Does it damage the system when removing?
Complete vs Partial: Does it move together or individually?

Question 14

Guiding

Answer 14

Translational, helical, rotational

Question 15

Motion transmission systems

Answer 15

Rotational to rotational
- Friction gears (Reversible) - no teeth
- Pulley belt (Reversible) - no teeth
- Gear Train (Reversible) - teeth
- Chain Sprocket (Reversible) - teeth
- Worm Gear (not reversible) - guitar pegs

Question 16

Formula for transmission speed and size

Answer 16

Speed A x Size A = Speed B x Size B

Question 17

Motion transformation system

Answer 17

Rotational to Translational (Vice versa)
Screw gear (nut fixed or screw fixed) - not reversible
Can follower (cam controls) - not reversible
Slider crank - reversible
Rack and Pinion (circle) - reversible