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MATSE 151: Composites > Lecture 1: Introduction > Flashcards

Lecture 1: Introduction Flashcards

1
Q

Composite materials are combinations of different material classes. What type of combination does it have to be though?

A

Macroscopic combinations (of any of the 4 metal classes).

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2
Q

True or false, composite materials are multiphase and never homogenous?

A

True.

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3
Q

What is the principle of combined action?

A

When these materials exhibit properties of both constituent phases significantly -> allows better combination of properties to be realized.

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4
Q

What are natural composites?

A

Composites existing in nature (i.e. existing in both plants and animals).

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5
Q

Give some examples of natural composites?

A

Wood, bones, muscles, etc.

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6
Q

Wood is a composite. Why?

A

It consists of the polymer of long cellulose fibers, and held together by a secondary phase/substance known as lignin. Separately, these two are weak, but together they form something strong.

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7
Q

What happens if cellulose is not binded with lignin?

A

It is much weaker.

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8
Q

What are the two constituents of bones? Which one is softer, and which is more brittle?

A

Hydroxyapatite
(calcium phosphate - more brittle/hard) and collagen (soft and flexible)

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9
Q

Recall: what is specific strength and specific stiffness?

A
  1. Strength/Density
  2. E/Density
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10
Q

What degree of specific strength and specific stiffness is usually needed for general use?

A

High specific strength, high specific stiffness

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11
Q

A higher specific strength and stiffness entails a higher what?

A

Higher structural efficiency.

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12
Q

Composites must generally be usable at higher operating temps, and are expected to be highly reliable and affordable. True or false?

A

True.

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13
Q

What are three criteria for engineered composite materials?

A
  1. recognizable interface between components
  2. distinct phases formed artificially
  3. tailored to produce unique combination of properties unattainable by the individual components
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14
Q

What are the two general constituents of a composite?

A

Matrix and dispersed phase

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15
Q

Which of the two composite constituents is generally more ductile and less hard?

A

The matrix.

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16
Q

The matrix is the ________ phase that surrounds the other phase in the mixture.

A

continuous

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17
Q

The dispersed phase is usually weaker than the matrix. True or false?

A

False. It’s stronger.

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18
Q

Is the dispersed phase usually continuous or discontinuous?

A

Discontinuous.

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19
Q

Properties of composites are a function of what? Give the three factors.

A
  1. properties of constituent phases
  2. their relative amounts
  3. geometry of the dispersed phase
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20
Q

Can composites be made from constituents with divergent linear expansion characteristics? Why or why not?

A

Might cause delamination. The phase that expands faster will push against the slower expanding phase. One phase is not allowing the other to expand, this causes tremendous stress developing at the interface. The fiber hence may come out of the matrix, and this manifests as a form of delamination or debonding.

21
Q

Both constituents (matrix and dispersed phase) may or may not be chemically reactive. True or false?

A

False, they must both be chemical inert and non-reactive.

22
Q

What is the first classification system for composites?

A

Based on the matrix material.

23
Q

What are the three mai types of composites under the first classification system?

A

MMCs, CMC, OMCs

24
Q

What are the two types of OMCs?

A

Polymer-matrix composites (PMCs) and carbon-matrix/carbon-carbon composties

25
Q

What was the main motivation of creating MMCs? Explain.

A

Extending structural efficiency of metals, while retaining their advantages, (including high chemical inertness, high shear strength, and good property retention at high temperature)

26
Q

In terms of service temperature, what is the advantage of MMCs?

A

They can be used at higher service temperatures compared to their metal counterparts.

27
Q

How are MMCs manufactured?

A

Dispersing a reinforcing material into a ductile metal matrix.

28
Q

What are the advantages of metal matrices (in terms of mechanical properties) compared to polymer matrices?

A

High strength, high fracture toughness, high stiffness

29
Q

Metal matrices can withstand higher temperatures and corrosive environments compared to polymer matrices. True or false?

A

True.

30
Q

What are 4 very popular metals used as a matrix or alloyed matrix?

A

Titanium, aluminum, magnesium, copper

31
Q

Since metals and alloys could be used as matrices, what has to be considered for the reinforcing material?

A

Reinforcing material needs to be stable at a wide range of temperatures, and also chemically inert.

32
Q

How come it is preferred for the interface between the matrix and the reinforcing phase to be smooth with no gaps?

A

This is to ensure better contact between the two phases, which will in turn lead to better load transfer.

33
Q

Why is it necessary for both constituents to be chemically inert non-reactive?

A

We don’t want the polymer matrix to oxidize or cause reactions. Interaction of the matrix with the fibers, which shortens the chain lengths, and this may cause the fibers to degrade, essentially weakening the material.

34
Q

For the reinforcing phase of MMCs, what may be used?

A

Particulates, continuous, and discontinuous fibers, whiskers, etc.

35
Q

Fact about CMCs!

A

These have high-temperature stability, high thermal shock resistance, high hardness, high corrosion resistance, light weight, nonmagnetic and nonconductive properties, and versatility in providing unique engineering solutions.

36
Q

What is the goal of ceramic reinforcement?

A

To provide toughness to the brittle ceramic matrix.

37
Q

OMCs were developed for aerospace applications during WWII. What material properties were needed?

A

Materials with high specific strength and high stiffness values (that were higher that currently existing materials).

38
Q

PMCs consist of what as a matrix and what as a dispersed phase?

A

Resin as the matrix, and fibers as the dispersed phase.

39
Q

What are the main fields where PMCs are used?

A

Aerospace, transpo, sports, infrastructures, biomedical engineering

40
Q

What is the second classification scheme for composites?

A

Based on the form of the reinforcing element.

41
Q

What are hybrid composites?

A

Composites with 2 or more different fibers in a single matrix.

42
Q

Why are hybrid composites used?

A
  1. have a better all-around combination of properties than composites containing only a single fiber type
  2. exhibits non-catastrophic failure
43
Q

What are the most common fibers for hybrid composites?

A

Carbon and glass (in polymeric resin)

44
Q

When hybrid composites are stressed in tension, failure is usually non-catastrophic. Why?

A

When the first fiber fails, the load is transferred to the other fiber present.

45
Q

What is catastrophic failure?

A

What the material collapses upon the application of load.

46
Q

Why do PMCs have low thermal expansion?

A

Polymer matrix is a poor conductor of heat. So when you heat it, it will absorb a good amount of heat and not reach the metal. Therefore the overall composite will not expand.

47
Q

Wood, carbon, glass, kevlar, etc. are examples of what?

A

Fillers for PMCs

48
Q

What are the advantages of PMCs?

A

Lightweight but high strength, good fatigue resistance, good corrosion resistance

MATSE 151: Composites (5 decks)

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