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Kerboodle textbook chapter 6

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35 Terms

1
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What is plastic deformation?

An irreversible change in the shape of an object due to a compressive or tensile force - removal of the stress or force produces permanent deformation

2
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What is elastic deformation?

  • A reversible change in the shape of an object due to a compressive or tensile force

  • If you remove the stress or force the object will return the to its original dimensions (there is no permanent strain)

3
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What does elastic mean?

When a material will return to it's original length when the load is removed

4
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Describe plastic behaviour

The material has a permanent change of shape when load is removed.

5
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What is elastic behaviour?

When a material returns to original dimensions when the load is removed.

6
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What is the elastic limit?

The value of stress or force beyond which elastic deformation becomes plastic deformation, and the material / object will no longer return to its original dimensions when the stress or force is removed

7
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State Hooke’s law

The force applied is directly proportional to the extension of the spring given the limit of proportionality is not exceeded.

8
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What is the force constant?

  • Force diveded by extension

  • It is called constant of proportionality k in Hooke's law, measured in Nm-1

9
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What is the the limit of proportionality?

The value of stress or force beyond which stress is no longer directly proportional to strain

10
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What is a yield point?

A point on a stress-strain graph beyond which the deformation is no longer entirely elastic

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Define ultimate tensile strength (UTS)

The maximum tensile stress that a material can withstand before it breaks

12
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Define stiffness

The ability of an object to resist deformation

13
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What is a polymeric material?

  • A material comprising of long-chain moleules (polymers) that does not obey Hooke’s law

  • May show large strains

  • Polyethene and Rubber are examples.

14
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What does brittle mean?

When a material shows very little plastic deformation before it brakes and deforms very little (if at all) under high stress

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What does ductile mean?

When the material has a large plastic region in a stress-strain graph, so can be drawn into wires. This means the material undergoes a large plastic deformation before it breaks.

16
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Define stress

The force per unit cross sectional area, measured in pascals (Pa)

17
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Define strain

The ratio of extension to original length.

18
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What is the unit of strain?

Strain does not have a unit as it is a ratio.

19
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Define young’s modulus

The ratio of tensile stress to tensile strain when these quantities are directly proportional to each other

20
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What is the unit of young’s modulus?

Pa or Nm-1

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What is the equation for young’s modulus?

E = σ/ε

Young’s modulus = tensile stress / tensile strain

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What is the eqaution for tensile stress?

σ = F/A

Tensile stress = force / cross-sectional area

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What is the equation for tensile strain?

ε = x/L

Tensile strain = extension / original length

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What is a compressive force?

Two or more forces together that reduce the length or volume of an object

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What is compressive deformation?

A change in the shape of an object due to compressive forces

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What is compression?

The decrease in length of an object when a compressive force is exerted on it

27
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What is are tensile forces?

Equal and opposite forces acting on a material to stretch it

28
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What is tensile deformation?

A change in the shape of an obiect due to tensile forces.

29
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What is a hysteresis loop?

  • A loop-shaped plot on a stress-strain or force-extension graph.

  • Obtained when, for example, loading and unloading a material produce different deformations

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What does the area of a hysteris loop represent on a force-extension graph?

The energy absorbed or released by the material

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What does the area of a hysteris loop represent on a stress-strain graph?

The energy absorbed or released per unit volume

<p>The energy absorbed or released per unit volume</p>
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What does the area under a loading curve on a force-extension graph represent?

The energy absorbed by the object during loading

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What does the area under a unloading curve on a force-extension graph represent?

The energy released by the object during unloading

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What does the area under a loading curve on a stress-strain graph represent?

The energy absorbed per unit volume by the object during loading

35
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What does the area under a unloading curve on a stress-strain graph represent?

The energy released per unit volume by the object during unloading