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Elements > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q

What material is this chapter about?

A

metals

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2
Q

When can you use a strain test?

A

If a load is static or changes relatively slowly with time and is applied uniformly over a cross section or surface of a member

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3
Q

When are strain tests most commonly conducted?

A

Metals at room temperature

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4
Q

What are the three principal ways in which a load may be applied?

A

Tension, compression, and shear

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5
Q

What is the principal way that strain tests are performed?

A

Tension

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6
Q

Why was the “dogbone” specimen configuration chosen?

A

So deformation is confined to the narrow center region and to reduce the likelihood of fracture at the ends of the specimen

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7
Q

What is the tensile testing machine designed to do?

A

Elongate the specimen at a constant rate and measure the applied load

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8
Q

In order to minimize the geometrical factors in tensile testing (such as area of a specimen) what parameters did they create?

A

Engineering stress and engineering strain

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9
Q

What is engineering stress’ relationship?

A

Force/cross-sectional area

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10
Q

What engineering strain’s relationship?

A

deformation elongation/ original length

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11
Q

In what direction does the specimen contract in a compression test?

A

Along the direction of the stress

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12
Q

Are compressive strains positive or negative?

A

Negative

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13
Q

When are compressive tests used?

A

When a material’s behavior under large and permanent strains is desired or when the material is brittle in tension

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14
Q

What is torsion?

A

A variation of pure shear in which a structural member is twisted and the torsional forces produce a rotational motion about the longitudinal axis of one end of the member relative to the other end

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15
Q

What are three examples of torsion?

A

Machine axles, drive shafts, twist drills

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16
Q

Through what relationship are stress and strain proportional?

A

Hooke’s law

stress= E (strain)

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17
Q

What is an elastic deformation?

A

A deformation in which stress and strain are proportional

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18
Q

What does the slope of a linear stress v. strain plot correspond to?

A

The modulus of elasticity

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19
Q

What can you think of the modulus of elasticity as?

A

Stiffness/ a material’s resistance to elastic deformation/ the resistance of separation of adjacent atoms

  • the greater the modulus, the stiffer the material
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20
Q

Is elastic deformation permanent?

A

No

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21
Q

On an atomic scale, what does macroscopic elastic strain look like?

A

Small changes in the interatomic spacing and the stretching to interatomic bonds

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22
Q

How does the modulus of elasticity relate between ceramics, metals, and polymers?

A

Ceramics and metals are about the same and polymers are lower

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23
Q

What is anelasticity?

A

The time-dependent elastic behavior (time it takes for the material to actually return to normal after deformed)

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24
Q

What is the anelastic component like in metals?

A

Small and often neglected

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25
Q

What is the anelastic component like in polymers?

A

In some the magnitude is significantly

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26
Q

Theoretically, what should Poisson’s ration be for isotropic materials?

A

1/4

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27
Q

What does elastically anisotropic mean?

A

The elastic behavior varies with crystallographic direction

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28
Q

Is plastic deformation permanent?

A

yes

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29
Q

From an atomic perspective, what does plastic deformation correspond to?

A

The breaking of bonds with original atom neighbors and then re-forming of bonds with new neighbors as large numbers of atoms

30
Q

What is a slip?

A

The process through which deformation is accomplished for crystalline solids

31
Q

How does plastic deformation in noncrystalline occur?

A

viscous flow mechanism

32
Q

How can you identify where plastic deformation begins on a stress strain curve? What is this point called?

A

When the line stops being linear

The proportional limit P

33
Q

What is the magnitude of the yield strength for a metal a measure of?

A

it’s resistance to plastic deformation

34
Q

What does the M point in a stress strain graph correspond to?

A

the maximum stress that can be sustained by a structure in tension

35
Q

At maximum stress, where is the deformation? What is the called?

A

deformation is confined at the neck. This is called necking.

36
Q

What is ductility?

A

A measure of the degree of plastic deformation that has been sustained at fracture

37
Q

What is the opposite of ductile?

A

Brittle

38
Q

What are the two ways you can numerically express ductility?

A

Percent elongation
Percent reduction in area

39
Q

What is fracture strain of a brittle material?

A

Less than 5%

40
Q

Do the magnitudes of yield and tensile strengths decline or increase with increasing temperature?

A

decline with increasing temperature

41
Q

What is the yield point phenomenon?

A

When the elastic-plastic transition is very well defined and occurs abruptly

42
Q

What occurs at the upper yield point?

A

Plastic deformation is initiated with an apparent decrease in engineering stress

43
Q

What is the lower yield point?

A

Where continued deformation fluctuates slightly about some constant stress value

44
Q

What is the magnitude of the yield strength of a metal a measure of?

A

It’s resistance to plastic deformation

45
Q

What is resilience?

A

the capacity of a material to absorb energy when it is deformed elastically and then to have this energy recovered

46
Q

What is the modulus of resilience?

A

Ur, the strain energy per unit volume required to stress a material from an unloaded state up to the point of yielding

47
Q

What are two characteristics of resilient materials?

A

high yield strength and low modulus of elasticity

48
Q

What is fracture toughness?

A

a property that is indicative of a material’s resistance to fracture when a crack is present

49
Q

What is notch toughness?

A

The ability of a material to absorb energy and plastically deform before fracturing.

50
Q

For a metal to be tough, what two characteristics must it display?

A

Ductile and strength

51
Q

Does the decline in the stress necessary to continue deformation past the maximum point M indicate that a metal is becoming weaker?

A

no. It is increasing in strength. the cross-sectional area is decreasing rapidly within the neck region.

52
Q

Where is the region of the true stress-strain curve?

A

From the onset of plastic deformation M to the point of necking

53
Q

Does necking occur in compression?

A

No

54
Q

What is hardness?

A

a measure of a material’s resistance to localized plastic deformation

55
Q

What is the most often performed mechanical test? Why?

A

Hardness

  1. Simple and inexpensive
  2. Test is nondestructive
  3. Tensile strength can be estimated from hardness data
56
Q

What are the four hardness tests?

A

Rockwell Hardness
Brinell Hardness
Knoop
Vickers

57
Q

What are both tensile strength and hardness indicators of?

A

A metal’s resistance to plastic deformation

58
Q

What are the two symbols for hardnes?

A

HB and HRC

59
Q

How do you calculate the modulus of resiliene?

A

The area under the elastic portion of the engineering stress-strain curve

60
Q

What are five factors that can lead to scatter in measured material properties?

A
  1. test method
  2. variations in specimen fabrication procedure
  3. operator bias
  4. apparatus calibration
61
Q

Do materials with large or small elastic moduli deform less?

A

Large

62
Q

What does the elastic modulus depend on?

A

Interatomic bonding forces

63
Q

What is Poisson’s ratio for metals, ceramics, and polymers?

A

Vmetals= 0.33
Vceramics= 0.25
Vpolymers = 0.40

64
Q

What are the 4 elastic constants?

A
  1. Young’s Modulus (E)
  2. Shear Modulus (G)
  3. Bulk Modulus (K)
  4. Modulus of Resilience (Ur)
65
Q

What kind of deformations are in the plastic region?

A

elastic and plastic

66
Q

What is the fracture strength?

A

Strength that the material breaks

67
Q

Visually, when does the maximum on the stress-strain curve appear for metals?

A

When it starts necking

68
Q

What is the toughness for metals, ceramics, and polymers?

A

Metals- large
ceramics/polymers- small

69
Q

Is there a lower or higher yield strength for the second deformation?

A

Higher

70
Q

What are the two things that a large hardness means?

A
  1. High resistance to deformation from compressive loads
  2. Better wear properties
71
Q

What is the hardness range for each scale? The useful range?

A

range: 0-130

useful: 20-100

Elements (15 decks)

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