Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Materials 1M03 > Mechanical Behaviour > Flashcards

Mechanical Behaviour Flashcards

1
Q

What is Stress?

A

Normalizes the force based on the cross-sectional area

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

What is Strain?

A

Normalizes the displacement based on the object size

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

What is Engineering Stress (σ)?

A

The instantaneous load applied to a specimen (in the direction of the applied force) divided by its original cross-sectional area.

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

What is Engineering Strain (ε)

A

The change in the gauge length of a specimen (in the direction of an applied force) divided by its original gauge length.

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

What is Shear Stress (τ)?

A

The instantaneous applied shear load divided by the original cross-sectional area across which it is applied.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is Shear Strain (γ)?

A

The tangent of the shear angle that results from an applied shear load.

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

Stress/Shear Behaviour

A

-A material will strain (ie. deform) in response to a stress
- The strain may or may not be permanent.
in engineering terms:
-Non-permanent : Elastic (disappears when stress is removed)
-Permanent : Plastic (remains when stress is removed)

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

What is the Modulus of elasticity?

A

(Young’s Modulus)

  • Ratio of stress to strain (slope)
  • Measure of the stiffness of a material
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the Shear Modulus?

A

For isotropic materials, shear and elastic modulus are related to each other by : E = 2G(1+v)
Elastic constant can simply be estimated by the stiffness of the bonds and # of bonds per unit area.
- Depends little on alloying
- Depends weakly on temperature in a crystalline solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Poisson’s Ratio?

A

Negative ratio of lateral and axial strains that results from an applied axial stress. Measures the lateral contraction during simple tension or compression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Plastic deformation?

A
  • Permanent after release of the applied load
  • Response can be ductile or brittle
  • Permanent atomic displacements
  • Upon removal of stress, atoms do not return to original positions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Yield Strength?

A
  • Yielding: the onset of plastic deformation
  • Yield strength (σy) : the stress required to produce a very specific amount of plastic strain ( a strain offset of 0.002 (0.2%) is commonly used).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is Work Hardening?

A
  • An increase in the yield strength due to plastic deformation
  • Temperature and composition significantly affect the hardening behaviour
  • Can change the strength of a material through deformation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is Ductility?

A
  • Relates to how much the material plastically deforms before it fractures
  • May be expressed as percentage elongation (%EL) or percentage reduction (%RA) from a tensile test
  • A material that experiences very little or no plastic deformation up to fracture is termed brittle.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Toughness?

A
  • Energy required to fracture a unit volume of material
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Energy Storage and Resilience

A
  • Resilience : capacity of a material to absorb energy when it is deformed elastically and then, upon unloading is able to recover this energy.
  • Means there must be a stored energy in the solid
17
Q

What is the Modulus of Resilience (Ur)?

A

the strain energy per unit volume

18
Q

What is Hardness?

A
  • A measure of a material’s resistance to local plastic deformation
  • Measures compressive and wear behaviour
19
Q

What are the advantages to hardness tests?

A
  • Cheaper, quick, non-destructive
  • used for quality control
  • works of quasi-brittle materials
  • used on specific parts of inhomogeneous materials, composites and thin films
20
Q

What are the disadvantages of hardness tests?

A
  • Less precise data, not useful for design calculations

- Relative measurement

21
Q

Quick Summary

A

Ceramics : high strength but very fragile
Metals : properties that are a good compromise between strength and ductility
Polymers : are weak at low temp and very ductile at high temp

22
Q

What are the characteristics of dislocations?

A
  • Cause distortions in the crystal
  • Lattice strain : zones of compression and tensions are created around the dislocation
  • Dislocations can exert a repulsive force on one another or an attractive force, resulting in annihilation
23
Q

What are Slip Systems?

A
  • Dislocations do not move with the same ease on all crystallographic planes and in all crystallographic directions
  • Typically there is a preferred plane and in that plane there are specific directions upon which dislocations can most easily move
  • Comprised of slip plane and slip direction
24
Q

Strengthening by grain size reduction

A
  • Dislocations can’t move across the grain boundary
  • Dislocations have to change their direction of motion
  • The greater the crystallographic mis-orientation, the more difficult the dislocation movement
  • Atomic disorder results in discontinuity of slip planes
  • Nano-grained materials exhibit exceptional strength compared to those with more conventional grain sizes
25
Q

Solid Solution Strengthening

A
  • Strengthening by adding solute atoms
  • Impurity atoms cause lattice strains, these strains repel dislocations and make dislocation motion more difficult
  • Lattice distortions are caused when the solute and host atoms are not the same size
26
Q

Precipitate Strengthening

A
  • A dislocation can easily move through an un-deformed crystal
  • The addition of small and hard second phase particles
  • Particles influence dislocation motion by acting as obstacles to motion and when dislocations are pinned at two ends by particles, they move in a frank read source
27
Q

Word Hardening

A
  • The motion of dislocations is hindered by the presence of other dislocations
  • A ductile metal becomes harder and stronger as it is plastically deformed, because the number of dislocations increases and thereby their mobility decreases
  • Dislocation density increases with deformation
  • Dislocations entangle with one another during cold working
  • As cold working increases : tensile and yield strength increase and ductility decreases
28
Q

What about Polymers?

A
  • Polymers deform considerably after necking (unlike metals)
  • Dislocations do not play a role in strength of amorphous solids
  • Impending the slippage of molecular chains can be done through blending, drawing, cross-linking and by reinforcement with particles, fibres and fabrics
29
Q

What is Annealing?

A
  • The material properties and characteristics of a cold-worked metal can be reverted back to the pre-cold worked state using a heat treatment
30
Q

Recovery (dislocations annihilate each other)

A
  • Small decrease in strength
  • Small increase in ductility
  • Grains are mostly unchanged
31
Q

Recrystallization (new strain free grains nucleate)

A
  • Rapid decrease in strength
  • Ductility is restored
  • New grains form
32
Q

Grain Growth (larger grains grow at expense of smaller ones)

A
  • Grain size increases

- small decrease in strength

Materials 1M03 (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions