1. The Technological World
Manufacturing Technical Objects
Chapter 12

2. Materials
Technical Objects: Objects humans have created and designed for a specific purpose
Their use exposes them to different types of stress which can cause the materials they are made of to deform.
Knowing what type of stress a technical object will be subjected to will allow manufacturers to determine which material is most appropriate for the creation of the object.

3. Materials
All technical objects are made up of one or more kinds of materials.
Each type of material has its own set of properties.
Ex: A bridge can be made out of steel and concrete.
Ex: A road can be made out of asphalt.

4. What is a Constraint?
A constraint describes the effect of an external force on a material.
**It is the resulting action of what happens to a material when it is exposed to an external force**
Ex: You step on a can and crush it.
The resulting action of the can after
it has been exposed to the external
force (your foot crushing it) is
compression (a type of constraint).

5. Compression Tension Torsion Deflection Shearing Type of Constraint
Description
Symbol
Examples
Compression
Crushing of material due to external forces
-hands squeezing a wet sponge
-a foot crushing a can
Tension
Stretching of material due to external forces
-copper stretched into a wire
-rope in a tug of war
Torsion
Twisting of material due to external forces
-an earthquake twisting a bridge
-hands wringing a wet towel
Deflection
Bending of material due to external forces
-a fish bending a fishing rod
-clothes weighing down a clothes line
Shearing
Cutting of material due to external forces
-scissors cutting paper
-metal cutters trimming shapes from sheets of metal

6. When a material has undergone a constraint, it becomes deformed.
Type of Deformation
Description
Elastic
Temporary change in shape or dimensions of the material. When constraint is removed, material returns to its original form.
Plastic
Permanent change in the shape or dimensions of material. Even when the constraint is removed, the material remains deformed.
Fracture
The constraint it so intense that the material breaks.

7. Example
A mountain climber is secured with a safety rope that holds her weight. Constraint: Tension Deformation: Elastic (rope will return to its original form once tension is removed)

8. Example (continued)
If the rope began to fray while holding the mountain climber, it would no longer return to its original shape once the tension was removed. Deformation in this case would be Plastic.

9. Example (continued)
If the rope broke while the tension was applied to it, the type of deformation would be Fracture because the material has broken.

10. Mechanical Properties of Materials
Mechanical Property
Definition
Hardness
Ability to resist indentation
Elasticity
Ability to return to their original shape after undergoing a constraint.
Resilience
Ability to resist shocks without breaking
Ductility
Ability to be stretched without breaking
Malleability
Ability to be flattened or bent without breaking
Stiffness
Resistance of an elastic material to deflection

11. Other Properties Property Definition Resistance to corrosion
Ability to resist the formation of rust or degradation by acids, salt, water, etc.
Electrical Conductivity
Ability to carry and electrical current
Thermal Conductivity
Ability to transmit heat

12. Try This!
Which mechanical property is sought in each of the following examples?
A plastic that keeps its shape even when twisted.
Wooden flooring that resists indentation by pointed objects, such as shoe heels.
A metal that stretches well to make wire.
A boat hull that resists shocks caused by running into shoals.
A material that bends easily, without breaking, to make gutters beneath a roof.

13. Degradation and Protection
Degradation: Decline in a material’s properties due to the effects of the surrounding environment.
Protection of a material: Application of a substance to a material to prevent or delay its degradation.

14. Categories of Materials
There are 2 categories of wood:
Hardwood  Deciduous trees
Softwood  Conifers
Hardness, resilience, elastic
Low thermal and electrical conductivity
Light weight

15. Modified Wood
Wood mixed with other substances (glue, plastics, preservatives)

16. Problems with Wood Decomposition (rotting)
Insect, fungi and microorganism infestations
These degradations reduce wood’s mechanical properties
Solutions:
1) Varnishing, painting, protective coatings
“Treated Wood” (more expensive)
Can be coated with a basic substance (turns wood green)

18. Ceramics
Solid material obtained from heating inorganic matter containing oxides (compound containing oxygen).
*Often made from sand or clay*
Low electrical conductivity
Hard
Resist heat
Fragile
Problems with Ceramics:
1) Acids and bases can degrade ceramics
2) A sudden change in temperature can
deteriorate the properties of ceramic

19. Metals and Alloys
Alloys are metals mixed with other metals or non-metals to make them more useful.
Ductile
Malleable
Good conductors of heat and energy
Problems with metals and alloys:
Rust
Solutions:
Coating with paint, grease, enamel...
Coating with other metals such as gold, chrome, zinc, etc.
“Quench hardening” and “Tempering”  rapidly heating and cooling them

20. Plastics Plastics are made from fossil fuels.
-Other substances can be added to plastics to obtain specific properties
-Poor conductors of heat and electricity
Thermoplastics
Become soft when heated and hard when
cooled (can be recycled)
Thermosetting Plastics
Remains permanently hard (more resilient)

21. Problems and Solutions for Plastic Degradation:
Liquid absorption (use a waterproof coating)
Oxidation (add antioxidant materials to plastic)
UV rays (add pigment that absorbs UV rays)

23. http://www. youtube. com/watch. v=Nh6lkv1udb0 http://www. youtube

24. Composites X A combination of materials from different categories
Contain 2 parts:
Matrix (skeleton, gives shape)
Reinforcement (fill the matrix to give strength)
Matrix
Reinforcement
Properties
Plastic X
Durable, light weight, resilient, inexpensive
Metal
Ductile, good conductor, stiff
Ceramic
Durable, heat resistant
Fibreglass
Stiff, corrosion resistant
Kevlar
Low density, resilient
Carbon
Stiff, low density, electrical conductor

25. Protection:
Both the matrix and the reinforcement need to be protected (they can fracture)
Strong adherence between the two parts is important
Uses:
-Airplane wings, engines, brakes
-sporting equipment (hockey sticks, helmets, skis)
-bullet proof vests