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Materials Screener > Chapter 5: Mechanical Properties > Flashcards

Chapter 5: Mechanical Properties Flashcards

1
Q

What is the fuel element cladding made of? and what primary function does it serve?

A

Zircaloy and its the first barrier to fission product release

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2
Q

What are some phenomena occurring in the cladding.

A

Pellet-clad interaction, hybride embrittlement, corrosion, creep

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3
Q

What type of alloys are used as a first wall in fusion?

A

Vanadium alloys

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4
Q

What is the main function of the fusion first wall?

A

separates low pressure plasma from high pressure cooland and neutron breeder.

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5
Q

Name the 4 key mechanical properties?

A

Elastic, Plastic, Creep and Cracking (Fracture)

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6
Q

What are some elastic mechanical properties?

A

youngs modulus, shear modulus and poissons ratio

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7
Q

What are some plastic mechanical properties?

A

Yield stress (hardness), ductility, ultimate strength

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8
Q

What are some key paraemeters of creep at high temperatures?

A

Rate and lifetime

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9
Q

What are the two main parameters of cracking?

A

Fatigue (cyclical stresses) and constant stress (stress corrosion cracking)

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10
Q

Initially pressure in coolant is higher than pressure in the interior for the cladding. What does this cause in terms of mechanical properties?

A

Creepdown of cladding onto pellets

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11
Q

Why does fuel overheats at EOL?

A

Fission gas releases primarly onto the center of the fuel therefore pressure inside is higher than pressure of coolant providing liftoff causing gap increases between fuel and cladding.

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12
Q

What do we call fuel pellet expansion due to fission product release?

A

Swelling

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13
Q

What do we call the deformation to the body under an applied stress?

A

Strain or displacement

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14
Q

What are the three main sources of stresses in a nuclear environment/

A

Applied External (ex. load), Thermal stresses (Strains causing thermal expansion), and Residual (from fabrication like welding aor thermal processing)

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15
Q

What happens in the Ultimate Tensile Stress?

A

Specimen necks down and the system is mechanically unstable (plastic instability)

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16
Q

What is the difference between engineering and True stress and strain?

A

Engineering are based on intial values of Ao and lo while True are corrected for area reduction and large strains.

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17
Q

What are the values in y and z in a uniaxial tension test?

A

All stress comopnents in y and z are zero.

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18
Q

What oes the elasticity theory relates?

A

It relates applied loads (Stress in a soild) to non-permanent displacements and strains.

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19
Q

How many compoents are in the stress tensor and what are the two categories?

A

Six components, three normal and three shear

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20
Q

Mention the three basic compoents of elasticity theory?

A

Equilibrium conditions that relate stress comp. to insure force balances on a volume element
Displacements and strain relations that insure the solid remains continuous as it deforms
Constitutive equations that relate stresses and strains.

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21
Q

What are displacements?

A

Changes in the position of a point as a result of applied stress

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22
Q

What is the elastic modulus in terms of the stress strain curve?

A

Describes the slope of the elastic portion in a stres strain curve but it fundamentally is related to the atomic binding.

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23
Q

What does the E-modulus (Youngs Modulus) depend on?

A

Orientation of the crystal.

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24
Q

What does having no texture mean in terms of mechanical properties?

A

Isotropic mechanical properties

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25
Q

What does having strong texture mean in terms of mechanical properties?

A

Anisotropic mechanical properties

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26
Q

What is hardness?

A

Is the measure of the resistance of a material against perfament shape change.

27
Q

What is the shape of vickers test?

A

4 sided pyramid

28
Q

What is the shape of Berkovich test?

A

3 sided

29
Q

What is the shape of a rockwell test?

A

Cone

30
Q

What is the shape of Brinell test?

A

Steel Sphere

31
Q

What is the shape of the knoop test?

A

Elongated pyramid

32
Q

What is elastic deformation?

A

Reversible displacement of crystal planes relative to each other where original structure is recovered when the stress is removed

33
Q

What is plastic deformation?

A

Is the permanent splippage of crystal planes which occurs above a critical stress.

34
Q

How will a single crystal plastically deform?

A

By shear on the plane with the highest resolved shear stress.

35
Q

What is the schmidt factor

A

cos(thetha) * cos(phi)

36
Q

What is the Protevin-Le Chatelier Effect?

A

Describes a serrated stress-strain curve which some material exhibit as they undergo plastic deformation specifically inhomogenous deformation. Effect associated with the competition between diffusing soluts pinning dislocations and dislocations breaking free of this stoppage.

37
Q

What are Luders Band?

A

Are localized bands of plastic deformation in metals experiencing tensile stresses due to inhibition of dislocation motion by interstitial atoms.

38
Q

Describe the four steps of ductile failure.

A

1) Necking
2) Formation of pores at impurities/inclusions
3) Joining of small pores to a crack
4) Final rupture at the highest shear stress in an angle (max shear stress)

39
Q

Describe the 3 Steps in brittle failure

A

1) Initial Dislocation motion
2) Moving dislocations costs more energy than nucleating a crack
3) Brittle fracture-cracking

40
Q

What is the best type of mechanical testing on brittle materials and why?

A

Compression tests since tension

41
Q

What is creep?

A

Time dependent mechanical deformation of solids which ocurrs slowly at stresses below the UTS.

42
Q

What differentiates creep from plastic deformation?

A

Time dependence

43
Q

What is dislocation glide?

A

movement of a dislocation on its slip plane. Usually, when we talk about glide, we’re talking about movement of a dislocation brought about by an applied shear stress on the slip plane

44
Q

What is dislocation climb?

A

movement of a dislocation perpendicular to its slip plane. This occurs when dislocations absorb or emit vacancies. It’s a diffusive process, requiring diffusion of vacancies towards or away from the dislocation core

45
Q

Steady state creep is a balance between…

A

strain hardening and thermal recovery

46
Q

What is coble creep?

A

Its a form of diffusion creep, is a mechanism for deformation of crystalline solid.

47
Q

When is coble creep dominant?

A

Lower stress levels and higher temperatures.

48
Q

What happens in coble creep?

A

Occurs through the diffusion of atoms in a material along the grain boundaries.

49
Q

What is Herring-Nabarro Creep?

A

Its a mode of deformation of crystalline materials.

50
Q

When is Herring-Nabarro Creep dominant?

A

At lower stress levels and higher temperatures in a fine grain material.

51
Q

What happens in nabarro creep?

A

Atoms diffuse through the crystals

52
Q

How does creep rate vary with grain size in Nabarro Creep?

A

Creep rate varies inverseley with the square of the grain size so fine-grained materials creep faster than coarser-grained ones

53
Q

What is the effect of precipitates in creep?

A

precipitates enhance creep resitance

54
Q

Creep depends on what three parameters?

A

Time, Temperature, Stress

55
Q

What is the Larson Miller Parameter?

A

means of predicting the lifetime of material vs. time and temperature using a correlative approach based on the Arrhenius rate equation.

56
Q

What two phenomena are responsible for superplasticity?

A

Grain Boundary Sliding and Grain Rotation

57
Q

What is the main reason we observe cladding deformation?

A

Due to strains induced by pellet thermal expansion

58
Q

Is radial or horizontal cracking first and why?

A

Radial since sigma_thetha > sigma_z

59
Q

What does cladding deformation resembles?

A

Bamboo

60
Q

How do we measure the ability of a material to withstand thermal stresses?

A

As the ratio of thermal stress to failure stress (either fracture or yelding)

61
Q

What are the three properties that a material must have to be considered good thermal failure resistent?

A

Large failure stress, thermal conductivity, low thermal expansion coefficient.

62
Q

What is radiation damage?

A

localized disruption of the crystall lattice of a solid (defect production) by high-energy radiation passing through it.

63
Q

What are radiation effects?

A

consequence of radiation damage on the mechanical and/or physical properties of the solid

64
Q

What are the three types of energetic particles?

A

Neutral Elementary particles, charged elementary particles and high energy atoms or ions.

Materials Screener (11 decks)

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