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Engineering GIC > Materials > Flashcards

Materials Flashcards

1
Q

State hooke’s law (2)

A

-The extension of a material is proportional to the load applied to it provided limit of proportionality is not reached
-F=KL

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2
Q

State 3 points which could determine if the material/graph follows hooke’s law (3)

A

-linear relationship = stress proportional to strain
-young Modulas
-no permemant deformation = after load is removed the material returns to its original shape

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3
Q

Define young modulus (2)

A

-is a property of material that measures its stiffness or how it responds to deformation

-stress/strain

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4
Q

State 3 main types of mechanical forces that act on a body (3)

A

1 tensile force
2 compressive
3 shear

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5
Q

Define tensile force (1)

A
  • a force that tends to stretch a material
  • increases the length of the material
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6
Q

Define compressive force (2)

A
  • a force that tends to squeeze or crush a material
    -will decrease the length of the material
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7
Q

Define shear force (4)

A

-a force that tends to slide on force of the material over an adjacent force
-shear stress occurs when the forces are not co planar
-the area on which the stress acts is parallel
-shear force causes a material to bend, slide or twist

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8
Q

Define stress (2)

A

-the ratio between force to cross sectional area of the material
-force/area

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9
Q

Define strain (2)

A

-the fractional change in a dimension of a material produced by a force
- change in length/ original length

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10
Q

State formula for percentage strain (1)

A

Change in length / original length x 100

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11
Q

State formula for area of wire (1)

A

(Pie x d2)/ 4

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12
Q

Convert 1mm2 to m2 (1)

A

1mm2 = 1x10-6 m2

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13
Q

State formula for shear modulus (1)

A

Shear stress/shear strain

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14
Q

Define elasticity and give examples (3)

A

-is the ability of a material to return to its original shape and size on the removal of external forces

-example= lead, plasticine

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15
Q

What type of energy is used in elasticity (2)

A

If deformation is elastic, all the work is stored as elastic strain energy in the material

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16
Q

Define limit of proportionality (3)

A

-the point on the graph where extension is no longer proportional to the applied force
-it is the point where the material stops obeying hooke’s law
-just beyond this point the material can behave in a non linear elastic manner

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17
Q

Define non linear elastic manner (1)

A

The relationship between stress and strain is not proportional

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18
Q

Define linear elasticity (1)

A

When the material obeys Hooke’s law so stress and strain are proportional

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19
Q

Explain what plasticity means and give examples (3)

A

-is the property of a material of being permanently deformed by a force without breaking
-it’s when a material does not return no it’s original shape when load is removed

-examples= copper, rubber, polyethene

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20
Q

State the energy transfer when plastic deformation occurs (1)

A

-if deformation is plastic, work is done to separate the atoms and energy is mostly dissipated as heat

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21
Q

How is plastic deformation used in real like scenarios (3)

A

-transport design
-crumple zones are designed to deform plastically in a crash
-energy goes into changing the shape of the vehicle

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22
Q

Define elastic limit (2)

A

-if the applied force is large it is found that material has become plastic and no longer returns back to its original length even after load is removed
-object passed the elastic limit shows plastic deformation

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23
Q

State and explain the behavior of ductile materials and give examples: (3)

A

-is the ability of a material to be plastically deformed by elongation without fracture
-it enables a material to be drawn out into wires
-examples: mild steel,copper,gold

24
Q

State and explain the behavior of brittle materials and give examples: (4)

A

-is a property of a material that can easily break without bending or stretching it
-they have no plastic state
-elastic state followed by immediate failure
-example: glass,concrete,bricks

25
Q

State and explain the behavior of malleable materials and give examples: (3)

A

-property of a material where it can be shaped when cold by hammering or rolling it
-capable of undergoing plastic deformation without fracture
-example: lead,gold

26
Q

State and example the key differences between brittle and ductile materials: (4)

A

1)Plastic deformation:

Ductile : undergo plastic deformation before failure

Brittle: fractures before undergoing plastic deformation

2) yield point:

Ductile: They have a yield point, they can be stretched or bent without fracture

Brittle: do not show yield point

3) deformation:

Ductile: undergo a lot of deformation before fracture

Brittle: undergo very little or no deformation before fracture

4) toughness:

Ductile: High toughness, they can absorb a lot of energy before fracture

Brittle: Low toughness, they can’t absorb energy before fracture

27
Q

How can stiffness of a material be determined (1)

A

By finding the gradient also called as the young modulus = stress/strain

28
Q

Define yield (1)

A

The point where the material starts to suddenly stretch without any extra load

29
Q

Define strength (1)

A

-measure of resistance of material to deform

30
Q

How is strength of materials determined (1)

A

-determined by reading of the ultimate tensile strength also called as breaking stress off the graph

31
Q

Define UTS or breaking stress (1)

A

The maximum stress a material can withstand

32
Q

Define toughness (1)

A

Measure of the materials ability to absorb energy (using charpys test to measure)

33
Q

Outline the method of charpys test (3)

A

-consist of striking a suitable specimen with a hammer on a pendulum arm while the specimen is held securely at each end
-the hammer strikes opposite the notch
-the energy absorbed by the specimen is determined by precisely measuring the decrease in motion of the pendulum arm

34
Q

Define creep (2)

A

-it is a high temprature progressive deformation at constant stress.
-it depends on time and temperature

35
Q

What is creep test used to evaluate (2)

A

-it is used to evaluate materials for boilers, gas, turbines, jet engines and ovens or any application that involves Hugh temperature under load
-it gives critical data for designing safe and reliable structures in industries where high temperature and stress are common

36
Q

State the types of advanced materials (4)

A

-ceramics
-semiconductors
-polymers
-composites

37
Q

State the types of engineering materials (5)

A

-semiconductor
-ceramics
-metals
-polymers
-composites

38
Q

State the structure of metals (2)

A

-atoms in metals are arranged in a regular, orderly pattern and vibrate in their fixed spaces

39
Q

State the properties of metals (3)

A

-conduct electricity
-strong
-ductile

40
Q

Define ceramics and state examples (2)

A

-ceramics are compounds formed between metallic and non metallic elements
-most frequently oxides, nitrides like Silicon dioxide, Aluminium oxide

41
Q

What does traditional ceramics mean (1)

A

-those compounds of clay minerals as well as cement and glass

42
Q

State the properties of ceramics (4)

A

-stiff
-hard
-brittle
-insulators

43
Q

What does polymers mean, define it (2)

A

-include familiar plastic and rubber materials
-many of them are organic compounds that are chemically based on carbon, hydrogen and other non metallic elements

44
Q

What are the properties of polymers (4)

A

-lightweight
-ductile
-easily processed
-insulators

45
Q

Define composites and state its properties (2)

A

-a composite is composed of 2 or more individual materials (metals,ceramics,polymers)
-light and strong

46
Q

Why do industries use ceramics, what is the goal of it (2)

A
  • is to achieve a combination of properties that is not displayed by any single material
    -to incorporate the best characteristics of each of the component materials
47
Q

State an example of ceramics and explain (4)

A

Fiberglass
-glass fibers are embedded within a polymer.
-the glass fibers are relatively strong and stuff but also brittle
-whereas the polymer is ductile but also weak and flexible
-which makes fiberglass relatively stiff,strong,flexible and ductile

48
Q

State the properties of ceramics (3)

A

-lightweight
-low density
-strong
-excellent thermal properties

49
Q

Define advance materials (2)

A

-materials that are used in high technology application
-which include semiconductors, biomaterials, smart materials

50
Q

State and explain the properties of semiconductors (2)

A

-electrical properties that are intermediate between electrical conductors and insulators

51
Q

explain crystalline material (1)

A

-atoms are self organized in a periodic array

52
Q

Explain single crystal (1)

A

-atoms are in a repeating or periodic array over the entire extend of the material

53
Q

Explain polycrystalline material (1)

A

-comprised of many small crystals or grains

54
Q

Explain amorphous (1)

A

-lacks a systematic atomic arrangement

55
Q

Which materials are used for making a laptop, can be multiple (3)

A

Composites: some may use composite materials as they are created by 2 or more materials with different properties
-because it’s high strength and light weight

Polymers: used for various part of the laptop including the keyboard
-because it’s light weight and durable

Metals : for structural components and casings
-because they are durable and High strength

56
Q

Define modulus of elasticity (2)

A

-the modulus of elasticity measures an objects resistance to being deformed when stress is applied on it

E = stress/strain

Engineering GIC (10 decks)

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