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ENGEN 112 > Mechanical Properties > Flashcards

Mechanical Properties Flashcards

1
Q

What is the equation for stress

A

Stress = force / area

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2
Q

What is the equation for strain

A

Strain = change in length / original length

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3
Q

Why do we use stress and strain instead of force and extension

A

Force and extension look at the dimensions of the sample, where as stress and strain look at the material itself

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4
Q

Draw a ductile stress strain graph

A

Look at example

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5
Q

Draw a brittle stress strain graph

A

Look at example

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6
Q

Where is the yield point/strength

A

Where the straight line begins to curve

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7
Q

Draw a proof stress graph

A

Look at example

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8
Q

Name the 3 primary bonds

A

Ionic
Metallic
Covalent

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9
Q

Name a secondary bond

A

Van der waals
Hydrogen bonding

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10
Q

What is the definition of crystaline?

A

Atoms that have long range order

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11
Q

What causes plastic deformation

A

Slip

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12
Q

What allows for slip to occur more easily

A

Dislocations

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13
Q

What is ductility

A

Amount of permanent/plastic deformation up till fracture

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14
Q

What unit is stress measured in

A

Pa

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15
Q

What do u multiple by to get M before a unit

A

X10^6

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16
Q

What do u multiple by to get G before a unit

A

X10^9

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17
Q

What section of the graph does stiffness relate to

A

Elastic region

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18
Q

What is the Young’s modulus equation

A

E = stress/strain

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19
Q

What are the units of Young’s modulus

A

Pa

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20
Q

What is the equation for true stress

A

True stress = load force/instantaneous area

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21
Q

Draw a graph comparing true stress and engineering stress

A

See example

22
Q

What equation is preferred when measuring ductility

A

%AR = (original area - final area)/ original area x100

23
Q

What is the term used to describe a material with no long range crystalline order

A

Amorphous

24
Q

What is the definition of hardness?

A

How easily a material can be scratched or dented

25
Q

What is a hardness test? (Steps)

A

Small indented forced into the surface of a material - size of dent created used to quantify hardness

26
Q

What does a big intent mean in terms of hardness for a material

A

Big indent means the material is soft

27
Q

Why are hardness tests commonly used

A

Simple, relatively inexpensive, non-destructive, used to infer other mechanical data

28
Q

What does a hardness test indicate

A

Resistance to plastic deformation

29
Q

Name a hardness test

A

Brinell hardness
Vickers and knoop

30
Q

What is variability (2)

A

Material properties are not exact quantities
Even with the same testing machine, variability of results will be achieved using samples cut from the same block of material

31
Q

What is impact toughness

A

The ability of a material to absorb kinetic energy up to fracture

32
Q

What are the four factors affecting toughness

A
  • the material
  • geometry (notches make it more brittle)
  • rate of loading
  • temperature
33
Q

Conditions of an impact test

A

Chosen to represent the most servers situation
- low temp
- high strain rate
- presence of a crack

34
Q

Impact toughness - affects of temperature

A

A material that is tough at room temp can become brittle at lower temps

35
Q

How is impact toughness tested (5)

A
  • sample has a notch in it
  • weighted pendulum of known mass is released
  • hits the sample (will now have known amount of kinetic energy)
  • samples breaks which requires energy
  • the more energy used the break the sample, lower the pendulum follow through
36
Q

What is a dipole

A

An uneven charge distribution

37
Q

What is poissons ratio

A

Relationship between how much material contracts in one orientation, while being stretched in the other orientation

38
Q

How to account for natural variability of mechanical properties in the real world

A

Use a safety factor or design factor in the designs

39
Q

How to account for variability of mechanical properties during lab testing

A

Test multiple identical samples, get an average and standard deviation

40
Q

What occurs during a bending test

A

Max compression on top surface
Max tension on bottom surface

41
Q

What is the neutral axis

A

Where neither compression or tension happens

42
Q

Why is %AR the preferred method

A

Gives more consistent/reliable results compared to %EL

43
Q

Why are FCC metals packed so closely together?

A

They are malleable, so it’s easy to change their shape
Because dislocations find it easy to travel in closely packed planes

44
Q

What happens to bonds during elastic deformation

A

Bonds stretch but no not break

45
Q

What are dislocations?

A

Imperfections in the crystal structure

46
Q

How do dislocations allow for easier plastic deformation

A

Fewer bonds need to be broken at once to achieve slip

47
Q

What is the UTS

A

The maximum stress before the material fails

48
Q

How does changing the length of a cable affect its maximum load

A

Changing the length would no affect the loading capacity
Load relates to stress (stress=force/area)
Length would affect the strain (strain=change in length/original length)

49
Q

What is engineering stress?

A

Defined as force/original area of the sample

50
Q

How will a notch affect a materials toughness

A

The crack will act as a stress concentrator
The material will show brittle behaviour in the presence of any defect

51
Q

Why r I beams used?

A
  • beam theory
  • compression and tension
  • material close to the middle is a waste
52
Q

Draw and label a SN curve for a ferrous metal and non-ferrous metal

A

Draw

ENGEN 112 (7 decks)

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