Mechanical Properties of Materials Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What is elastic deformation?

A

Elastic deformation is when there is no permanent deformation after a load is removed from a material, due to bonds being able to return to their normal length.

  • Strongly bonded materials require a greater force in order to pull apart and deform the bonds.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is plastic deformation?

A

Plastic deformation is when there is a permanent deformation after a load is removed from a material, due to bonds being unable to return to their normal length.

  • Instead of stretching bonds, they are broken or reformed with new neighbours causing a large number of atoms to move relative to each other.
  • Stress is no longer proportional to strain.
  • Dislocations cause this plastic deformation. Mainly associated with metals.
  • Although the crystal structure doesn’t change, the shape of the material does.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Young’s modulus?

A

A measure of the stiffness and bond strength of a material.

  • E = σ/ε (during elastic deformation)
  • N/mm2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Poisson‘s ratio?

A

The ratio of lateral to axial strains.

  • v = εL
  • Dimensionless
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are auxetic materials?

A

Auxetic materials have a negative Poisson’s ratio, and so expand in all directions when under tension.

  • They are frequently used in memory foam beds.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the features of a stress-strain graph?

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How can you improve the accuracy of a reading for Young’s modulus?

A

Draw a parallel line through the yield point and measure the gradient of this line.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is yield strength?

A

The yield strength is the point at which areas is no longer proportional to strain.

  • Above this level of stress, plastic deformation occurs.
  • It is a measure of resistance to plastic deformation.

Metals:

  • Variable yield strength from low to high.

Ceramics:

  • Hard to measure, as fractures usually occur before yield.

Polymers:

  • Low yield strength.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is tensile strength?

A

The tensile strength is the maximum stress that a material can sustain.

  • It is the maximum stress shown on a stress-strain curve.
  • It occurs in metals once noticeable necking starts, and in polymers when the polymer backbone chains are aligned and about to break.

Metals:

  • High tensile strength.

Ceramics:

  • Medium tensile strength.

Polymers:

  • Low tensile strength.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is ductility?

A

The ductility is the degree of plastic deformation before failure.

  • It can be found by drawing a line parallel to the Young’s modulus to find the plastic strain at failure of the material.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is toughness?

A

Toughness is the energy required to break a unit volume of a material.

  • It is a measure of the ability of a material to absorb energy up to fracture, or the resistance to fracture once a crack is present.
  • It can approximately be found by the area underneath a stress-strain curve.
  • Generally, ductile materials are tough, and brittle materials are not.
  • Jm-3

Metals:

  • Large toughness.

Ceramics:

  • Low toughness.

Polymers:

  • Low toughness.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is resilience?

A

Resilience is the capacity of a material to absorb energy during elastic deformation and recover energy during unloading.

  • It is the materials ability to store energy.
  • The modulus of resilience (U) is the strain energy per unit volume required to stress a material to the yield point.
  • Jm-3
  • U = 1/2σyεy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is hardness?

A

Hardness is the resistance to localised plastic deformation (such as dents/scratches).

  • Large hardness means resistance to plastic deformation is great and so materials wear better.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the different types of hardness test?

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Mohs hardness scale?

A
  • A scale of hardness devised by arranging 10 minerals so that one material could only scratch those below it.
  • Intervals of hardness are approximately equal except for between corundum and diamond.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly