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Materials > Stress, Strain and Moduli > Flashcards

Stress, Strain and Moduli Flashcards

Lectures 2 and 3

1
Q

What is elastic/plastic deformation?

A

materials deform in response to load, at a high enough load they break

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2
Q

What is the difference between elastic and plastic deformation?

A

Elastic deformation is recoverable
Plastic deformation is permanent

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3
Q

What kind of deformation do ductile materials experience (e.g. metals)?

A

Elastic and plastic deformation

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4
Q

What kind of deformation do brittle materials experience (e.g. glass and concrete)?

A

Minimal plastic deformation

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5
Q

What is Stress?

A

Force over area
Measured in Pa (Nm^-2)

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6
Q

What is Strain?

A

Fractional change in dimensions, dimensionless (may be reported in %)

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7
Q

What is the equation for Normal stress?

A
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8
Q

What is the equation for Normal strain?

A
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9
Q

What is the equation for Young’s modulus (also known as Elastic modulus)?

A
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10
Q

What may Young’s/Elastic modulus be referred to?

A

also referred to as stiffness

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11
Q

What is the Young’s modulus?

A

The materials property

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12
Q

What is Poisson’s ratio?

A

Measure of the contraction in the direction perpendicular to the applied stress

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13
Q

What is the equation for Poisson’s ratio?

A
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14
Q

What is Poisson’s ratio?

A

a material property

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15
Q

What are typical values for Poisson’s ratio?

A

Positive for most materials but theoretical range for isotropic (looks the same in all directions) materials
Materials with negative Poisson ratios tend to have special cellular structures

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16
Q

What is Shear stress, strain and modulus?

A

If the forces are applied parallel to the surface then it is shear.

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17
Q

What is the equation for Shear Stress?

A
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18
Q

What is the equation for Shear Strain?

A
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19
Q

What is the equation for Shear modulus?

A
20
Q

What is the equation for the shear modulus of the material being isotopic?

A
21
Q

What is the Shear modulus?

A

a material property

22
Q

What is the relationship between the Young’s and shear modulus for a typical metal?

A
23
Q

What is the equation for Volumetric strain?

A
24
Q

How can tension affect the volume of a shape?

A

Can involve changes in volume, but these are generally small

25
Q

What does Shear involve?

A

No change in volume, only a change in shape

26
Q

What does hydrostatic pressure cause?

A

Hydrostatic pressure causes changes in volume

27
Q

What is the equation for Bulk modulus

A
28
Q

In the equation B = - P/(deltaV/V) what does the minus sign indicate?

A

The minus sign indicates compression

29
Q

What is the bulk modulus?

A

a material property

30
Q

What is the equation for the bulk modulus for an isotropic material?

A
31
Q

For a typical metal the relationship between the Young’s modulus and the bulk modulus is?

A

B = E

32
Q

Applied forces result in?

A

Stress(es) in a body
Strain(s) or changes in the dimensions of a body

33
Q

Stress and strain are related by material properties

A

Moduli
- Young’s modulus (GPa)
- Poisson’s ratio (dimensionless)
- Shear modulus (GPa)
- Bulk modulus (GPa)

34
Q

What is an isotropic material?

A

Materials that have uniform properties in all directions (e.g. window glass)

35
Q

How many moduli do we need to relate stress to strain in isotropic materials?

A

Only need 2 (out of 4) moduli to relate stress to strain in isotropic materials (i.e. any 2 of E, V, G and B)

36
Q

What materials can we treat as isotropic?

A

Can treat many materials as being isotropic (on a large scale)
- e.g. metals, ceramics etc. because they contain many randomly oriented grains

37
Q

What materials are not isotropic?

A

Wooden table, Fibre glass fabric, plywood

38
Q

How many unique components of stress are there?

A

6 unique components of stress - 3 normal stresses and 3 shear stresses

39
Q

How many unique components of strain are there?

A

6 unique components of strain - 3 normal strains and 3 shear strains

40
Q

Non-isotropic materials?

A

If transversely isotropic e.g. wood - 5 independent moduli needed
If orthotopic e.g. plywood - 9 independent moduli needed

41
Q

What is the graph for young’s modulus?

A
42
Q

What are the three equations of normal strain are related to normal stresses?

A
43
Q

What are the three equations of shear strain that are related to shear stresses?

A
44
Q

How can the 3 normal stresses and 3 shear stresses be presented?

A
45
Q

A steel object with E = 210GPa, v = 0.33 is subject to the following stresses σ xx = 100MPa, σ yy = -20MPa, σ xy = 100MPa and σ zz = 50MPa. Is the strain ε xx equal to?

A
46
Q

A steel object with E = 210GPa, v = 0.33 is subject to the following stresses σ xx = 100MPa, σ yy = -20MPa, σ xy = 100MPa and σ zz = 50MPa. Is the strain ε xy equal to

A
47
Q

What are the equations for plane stress in isotopic materials that applies to thin sections

A

Materials (10 decks)

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