# EGN 3365 Exam 2

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The given stress-strain graph represents?

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### 77 Terms

1

The given stress-strain graph represents?

Elastic then plastic deformation

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2

What does the figure represent?

Simple compression

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3

Which material has the highest toughness?

Material 2

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4

For an engineering strain of 1, calculate percentage elongation (ductility) of the specimen?

100

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5

A specimen of copper having a rectangular cross-section 15.2 mm X 19.1 mmĀ  is pulled in tension with 44,500 NĀ  force, producing only elastic deformation. Calculate the resulting strain. ( Elastic modulus of copper = 110 GPa)

1.39 x 10^-3

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6

Ductility is the amount of plastic deformation at failure.

From the given graph below, determine which line represent a material with high ductility and which line represent a material with low ductility.

Blue line: Low ductility.

Green line: High ductility.

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7

For some metal alloy, the true stress of 345 MPa produces a plastic true strain of 0.02. How much does a specimen of this material elongate when true stress of 415 MPa is applied if the original length is 500 mm? Assume a value of 0.22 for the strain-hardening exponent, n.

23.7mm

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8

Poisson's ratio for metals, ceramics and polymers is in the range:

0.15 < v <= 0.5

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9

Deformation of a sample to an engineering strain of 2 means that the sample is ___________ its original length.

A. Half

B. Twice

C. Three times

D. 2% longer than

Three times

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10

What best describes the figure?

A. Not an example of diffusion

B. Left: before diffusion, right: after diffusion

C. Left: after diffusion, right: before diffusion

D. None of the above

Left: before diffusion; right: after diffusion

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11

What is diffusion

Mass transport by atomic motion

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12

Atoms tend to _____________ from regions of _____________ concentration to regions of _____________ concentration.

Migrate, high, low

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13

What is self-diffusion?

Migration of host atoms in pure metals

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14

What is the derivation of the equation relating the diffusion coefficients at two temperatures T1 and T2, given that:

Dā = Dāexp [-Qd/R(1/T2-1/T2)]

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15

At 300Ā°C the diffusion coefficient and activation energy for Cu in Si are

Dā (300Ā°C) = 7.8 Ć 10ā»ā»Ā¹Ā¹ mĀ²/s

Qd = 41.5 kJ/mol

Compute the diffusion coefficient Dā at 400Ā°C.

28.46 Ć 10ā»ā»Ā¹Ā¹ mĀ²/s

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16

Non-steady state diffusion is a function of:

Time and position

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17

Fickās first law of diffusion is applicable to

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18

Whatās Fickās second law of diffusion?

dC/dt = D dĀ²C/dxĀ²

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19

What's Fickās first law of diffusion?

J = āD dC/dx

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20

Whatās the relationship between the diffusion coefficient and temperature?

Increases with increasing temp

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21

What is interdiffusion?

Diffusion of atoms of one material into another material

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22

Diffusion rate of vacancy diffusion depends on

Number of vacancies, activation energy

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23

interstitial diffusion

smaller atoms diffuse between adjacent atoms, faster than vacancy diffusion

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24

Case hardening is an example of _________ diffusion

Interstitial

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25

case hardening

outer surface is hardened by diffusing carbon atoms into surface

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26

Doping

adding impurities to a semiconductor to increase conductivity

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27

Process of doping

1. P rich layers on surface

2. Heat it

3. Doped semiconductor regions

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28

Diffusion is faster for

open crystal structures, materials with secondary bonding, smaller diffusing atoms, lower density materials

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29

If a specimen is being elongated or extended

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30

Specimen is compressed or contracted

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Deformation

Change in dimension

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shear forces

Parallel to cross sectional area

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33

Plastic deformation

permanent change in shape by bending and folding

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Elastic deformation

material returns to original state when stress is removed

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Common states of stress

Simple tension, torsion, simple compression, bi-axial tension, hydrostatic compression

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36

Yield strength

point where the material begins to plastically deform

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Toughness

the ability of a material to resist fracture

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Hardness

resistance to localized surface deformation and compressive stresses

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Resilience

Ability of a material to store energy

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40

Ductility

amount of plastic deformation at failure

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41

Engineering stress

tensile, shear

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Engineering strain

tensile, lateral, shear

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Percent elongation

the total percent increase in length of a specimen during the tensile test

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Dislocation

A defect where atoms are misaligned around it

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45

Edge dislocation

extra half plane of atoms inserted into a crystal structure

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Dislocation line

The line where dislocations happen

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Screw dislocation

lattice plane shifts similar to a spiral staircase

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Burgers vector

measure of lattice distortion

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Twin boundary

a reflection of atom positions across the twin plane

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Solidification

Result of casting molten material

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Grain boundaries

Regions between grains (crystals)

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Point defects

vacancy, interstitial atoms, substitutional atoms

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53

Vacancies are

vacant atomic sites

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Dislocations move when

Stresses are applied

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55

A catalyst ____________ the rate is a chemical reaction without being consumed

Increases

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Dislocation types include

Edge, screw, and mixed

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two diffusion mechanisms

vacancy and interstitial

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58

The applied mechanical force is normalized to

Stress

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59

The degree of deformation is normalized to

strain

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Elastic deformation is

nonpermanent and reversible

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Plastic deformation is

permanent and nonrecoverable

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Stiffness

a material's resistance to elastic deformation

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Strength

A materials resistance to plastic deformation

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64

In an optical microscope, grain boundaries appear as white lines after the surface is prepared by etching. T/F

false

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65

According for Fickās first law, the concentration of diffusing species is a function of both time and position. T/F

false

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D_interstitial << D_substitutional

T/F

false

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67

In edge dislocation, burgerās vector is perpendicular to dislocation line. T/F

true

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68

Diffusion coefficient _________ with increasing temperature

increases

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69

What are the interfacial defects?

twin boundaries, grain boundaries, stacking faults

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70

I can observe individual atoms using an optical microscope. T/F

false

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71

Whatās an example to processing using diffusion

case hardening

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72

Interstitial diffusion is more rapid than vacancy diffusion. T/F

true

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73

Equiaxed grains are

Roughly the same dimension in all directions

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74

Columnar grains are

grains elongated in one direction

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75

Rate of diffusion is __________ of time

independent

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76

Diffusion is ____________ of time

dependent

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77

What are the 5 interfacial defects?

external surfaces, phase boundaries, optical boundaries, twin boundaries, stacking faults

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