Composite Engineering Materials Review

Manufacturing Knowledge Menu

A composite is a material consisting of two (or more) different materials bonded together, one forming a ‘matrix' in which are embedded fibers or particles that increase the strength and stiffness of the matrix material.

A natural composite is wood in which cellulose fibers are embedded in a lignin matrix. Concrete is a composite in which particles of stone add strength with a further increase in strength provided by steel reinforcing rods. Vehicle tires consist of rubber reinforced with woven cords.

Plastics are reinforced with glass, carbon and other fibers. The fibers may be unidirectional, woven or random chopped. Metals, carbon and ceramics are also used as matrix materials.

So-called ‘whiskers', which are single crystals of silicon carbide, silicon nitride, sapphire, etc., give extremely high strength.

Typical engineered composite materials include:

  • Composite building materials such as cements, concrete
  • Reinforced plastics such as fiber-reinforced polymer
  • Metal Composites
  • Ceramic Composites (composite ceramic and metal matrices)

Composite materials are generally used for buildings, bridges and structures such as boat hulls, swimming pool panels, race car bodies, shower stalls, bathtubs, storage tanks, imitation granite and cultured marble sinks and counter tops. The most advanced examples perform routinely on spacecraft in demanding environments.

Elastic modulus of a composite (continuous fibers in direction of load)

Let:
Ef = modulus of fibers
Em = modulus of matrix
Ec = modulus of composite
r = (cross-sectional area of fibers) / (total cross sectional area)
Ec  = r Er + ( l - r ) Em

Acronyms for composites

FRP fiber-reinforced plastic
FRT fiber-reinforced thermoplastic
GRP Glass-reinforced plastic
GRC Glass-reinforced composite
CFC Carbon fiber composite
CFRP Carbon-fiber-reinforced plastic
CFRT Carbon-fiber-reinforced thermoplastic

Forms of fibers for composites

Fiber: length over 10 times the diameter; diameter less than 0.25 mm.

  • Filament: a continuous fiber.
  • Wire: a metallic fiber
  • Whisker: a fiber consisting of a single crystal.

Arrangement of fibers in composites

Type
Arrangement
Comments
Unidirectional
Unidirectional
Load taken in direction of fibers. Weak at right angles to fibers
Bidirectional
Bidirectional
Takes equal load in both directions. Weaker since only half the fibers used in each direction
Multidirectional
Multidirectional
Load capacity much reduced but can take load in any direction in plane of fibers
WovenMat
Woven Mat
Similar to bidirectional however easy to handle
Random, Chopped
Random Mat‚Äč
Low in strength but multidirectional. Has handling advantages

Properties of some fibers, wires and whiskers used in composites

Material
Type
Density
(kgm-3)
Young's Modulus
(GNm-2)
Tensile Strength
(Nmm-2)
Filament diameter
(µm)
E Glass
Fiber
2,500
62
3,500
205
Carbon
Fiber
2,500
415
1,750
705
Silica
Fiber
2,500
72
6,000
5.0
18/8 Stainless Steel
Wire
7,900
205
2,100
150
Tungston
Wire
19,300
350
2,900
150
Tungston
Wire
19,300
350
3,800
25
Graphite
Whisker
2,200
675
21,000
-
Sapphire
Whisker
4,000
525
6,000
-
Silicon Carbide
Whisker
3,200
690
21,000
-
Silicon Nitride
Whisker
3,100
380
14,000
-

 

Contribute Article
Spider Optimizer

© Copyright 2000 - 2017, by Engineers Edge, LLC www.engineersedge.com
All rights reserved
Disclaimer | Feedback | Advertising | Contact


User Reviews/Comments:

There are currently no comments available.


Add a Comment (you must be logged in to post comment Register):
Name:
Email: (Optional)
Comment: