MSE 2034 > Chapter 16 > Flashcards

Chapter 16 Flashcards

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1
Q

What is a composite?

A
  • A combination of two or more individual materials
  • Multiphase material that is artificially made
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2
Q

What are the two different phase types?

A
  1. Matrix
  2. Dispersed
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3
Q

What is the matrix phase type?

A

The continuous phase that surrounds the dispersed phase

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4
Q

What is the dispersed phase type?

A

Discontinuous phase and is surrounded by the matrix phase

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5
Q

What is the purpose of the matrix phase?

A
  • Transfer stress to the dispersed phase
  • Protect the dispersed phase from the environment
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6
Q

What are the main types of composites?

A
  1. MMC (metal matrix composite)
  2. CMC (ceramic matrix composite)
  3. PMC (polymer matrix composite)
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7
Q

What is the goal of composites?

A

To obtain a more desirable combination of properties

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8
Q

What are the types of dispersed phases?

A
  • Particle
  • Fiber
  • Structural
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9
Q

What is the purpose of a dispersed phase in an MMC?

A

To increase yield strength, tensile strength, and creep resistance

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10
Q

What is the purpose of a dispersed phase in a CMC?

A

To increase fracture toughness

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11
Q

What is the purpose of a dispersed phase in a PMC?

A

Increase Young’s Modulus (stiffness), yield strength, tensile strength, and creep resistance

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12
Q

What are the four main classes of composites?

A
  • Particle-reinforced
  • Fiber-reinforced
  • Structural
  • Nano
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13
Q

What are the two types of particle-reinforced composites?

A
  • Large-particle
  • Dispersion-strengthened
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14
Q

What are the two types of fiber-reinforced composites?

A
  • Continuous (aligned)
  • Discontinuous (short)
    > Aligned or randomly oriented
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15
Q

What are the two types of structural composites?

A
  • Laminates
  • Sandwich panels
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16
Q

What are some examples of particle-reinforced composites?

A
  • Spheroidte steel
    > Ferrite matrix (ductile) & cementite (brittle)
  • WC/Co cemented carbide
    > Cobalt matrix (ductile, tough) & WC (brittle, hard)
  • Automobile tire rubber
    > Rubber matrix (compliant) & carbon black (stiff)
  • Concrete
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17
Q

What is the composition of concrete?

A
  • Gravel
  • Sand
    > Sand fills the voids between gravel
  • Cement
  • Water
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18
Q

What are the types of concrete treatments?

A
  • Reinforcing
  • Prestressing
  • Posttensioning
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19
Q

What is reinforced concrete?

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A
  • Concrete reinforced with steel rebar or remesh
  • Increases strength, even if concrete matrix cracks
20
Q

What is prestressed concrete?

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A
  • Rebar/remesh is placed under tension during setting
  • Tension is released after setting which places concrete in compression
  • To fracture, tensile stress must exceed the compressive stress
21
Q

What is posttensioned concrete?

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A
  • Nuts are placed on ends of rebar
  • Tightened to place concrete under compression
22
Q

What is the rule of mixtures?

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A
  • The properties of a composite are based on an average of the properties of the constituents
  • Often based on volume
23
Q

What is dispersion strengthening?

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A
  • Dispersing very small particles of a hard, inert phase within a load-bearing matrix phase
  • Particles hinder displacement motion
24
Q

What is large-particle strengthening?

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A
  • Larger particles are placed within a matrix
  • Matrix transfers stresses to particles
25
What are the properties of particle-reinforced composites?
Isotropic
26
Why are fibers used to reinforce composites?
Fibers are very strong in tension
27
What is fiber-glass?
- Glass fibers in a polymer matrix - Fibers provide strength and stiffness - Polymer matrix holds, protects, and transfers loads to fibers
28
What are the three fiber types?
- Whiskers - Fibers - Wires
29
What are whiskers?
- Thin single crystals with large length-to-diameter ratios - High crystal perfection, making extremely strong - Expensive and hard to disperse
30
What are examples of whiskers?
- Graphite - Silicon nitride - Silicon carbide
31
What are fibers?
- Polycrystalline or amorphous - Generally polymers or ceramics
32
What are some examples of fibers?
- Alumina - Aramid - E-glass - Boron - UHMWPE
33
What are wires?
- Metal wires with relatively large diameters Ex: steel, molybdenum, tungesten
34
What is the difference between longitudinal and transverse directions?
Longitudinal: along fiber alignment Transverse: across fiber alignment
35
What are the three types of fiber alignments?
- Aligned continuous (longer fibers) - Aligned (shorter fibers) - Random
36
What are the properties of fiber-reinforced composites?
Isotropic or anisotropic
37
What are examples of applications of discontinuous fibers?
- Disk brakes - Gas turbine exhaust flaps - Missile nose cones
38
What is the critical fiber length?
- Length for effective stiffening and strengthening > Depends on tensile strength, diameter, and matrix shear strength
39
How does the efficiency of short and long fibers compare?
- Short, thick fibers are less efficient than long, thin fibers - Short fibers cannot reach maximum strength - Long fibers can maintain maximum stress for longer
40
What are the efficiency factors of fibers?
K = 1 when aligned parallel K = 0 when aligned perpendicular
41
What is pultrusion?
1. Continuous fibers are pulled through a tank of resin and covered in a thermoset 2. Fibers pass through a die and are preformed to a shape 3. The preformed shape passes through a die that imparts the final shape and cures the thermosetting resin
42
What are the two types of composite production methods?
- Pultrusion - Filament winding
43
What is pultrusion used for?
- The manufacture of components having continuous lengths and a constant cross-sectional shape (rods, tubes, beams, etc.)
44
What is filament winding?
1. Continous fibers are positioned in a pattern to form a hollow shape 2. Fibers are covered in a thermosetting resin 3. Fibers are wound onto a mandrel 4. After the desired amount of layers is added, thermoset is cured either in an oven or at room temperature 5. Mandrel is removed and final product is left
45
What are the three types of winding?
- Helical (helix) - Circumferential (circular) - Polar (pole to pole)
46
What are laminates?
- Stacked and bonded fiber-reinforced sheets - Have stacking sequences - Balanced in-plane stiffness
47
What are sandwich panels?
- Two strong/stiff outer faces with a lightweight core - Results in low density and high bending stiffness Ex: honeycomb core between two facing sheets
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