Composites - Lecture 3 - Material Engineering, Lecture notes of Material Engineering

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What is a prepreg?

1

Prepregs

When selecting prepregs the maximum service

temperature is one of the key selection criteria

for choosing the prepreg matrix.

The cure can be simply represented by pre-

polymers whose reactive sites join together

forming chains and cross linking. Once this

process has taken place the polymer is fully

cured.

The thermoset cure essentially joins the reactive

sites together with the help of added

components (filler, accelerator, hardener,

thermoplastic resins).

Sports

• Over the years, in many different sports, material science

has brought great performance advancements. Let's take

a brief look back at the history of several different sports.

• GOLF

Ben Hogan used to play with wooden shafted golf clubs.

Then, in the 1940's, golf shafts became steel. It was not

until the late 1980's that we started to see Carbon Fiber

used in golf shafts. Today, Tiger Woods and all PGA golfers

are using clubs that are made with Carbon Fiber.

• TENNIS

Bjorn Borg and Chris Evert played at Wimbledon with

wooden rackets. Then, in the 1980's, Jimmy Connors

started to win using a metal Wilson T-2000 racquet. Today,

all tennis racquets are made of Carbon Fiber. To the right,

Roger Federer is seen winning Wimbledon with his Carbon

Fiber tennis racquet.

More Sports

• WATER SKIS

When water skiing began in 1922, skis were made of wood.

It was not until the early 1970's that EP Water Skis

developed a fiberglass/foam core water ski. In 1994,

GOODE Skis developed the world's first Carbon Fiber water

ski. Carbon Fiber skis are now used by all World Champions

and World Record Holders.

• SKI POLES

Ski poles were constructed of bamboo. Then, during World

War II, ski poles were made of steel. In 1958, Ed Scott

invented the aluminum ski pole. It took another 31 years

before Dave Goode invented the World's first Carbon Fiber

ski pole.

• OTHER SPORTS

There are many, many other sports that have benefited

from the use of Carbon Fiber (hockey, cycling, archery, etc.).

 Cross section of a high

performance ski.

 The function and

material of each

component is listed.

• Carbon Fiber, weighs

about 1/2 of a traditional

wood core/fiberglass ski

(typical 175cm GOODE ski

weighs only 2.1lbs).

• The layered Carbon Fiber

used in all GOODE Skis has

twice the strength of

fiberglass (3.5 times the

strength of aluminum) while

weighing half as much. That

is a four times (4X) Strength

to Weight Ratio.

Snow Boards

8

handmade

honeycomb

core.

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Sandwich Construction

Advantages: very low weight, high stiffness,

durable, design freedom, reduced production

costs.

• Tensile and compression stresses are

supported by the skins

• Shearing stress is supported by the

honeycomb

• The skins are stable across their whole length
• Rigidity in several directions
• Excellent weight saving

ANALOGY BETWEEN AN I-BEAM

AND A HONEYCOMB SANDWICH

CONSTRUCTION

Helicopters

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Classification: Particle-Reinforced (ii)

Concrete – gravel + sand + cement + water

• Why sand and gravel? Sand fills voids between gravel particles

Reinforced concrete – Reinforce with steel rebar

• increases strength - even if cement matrix is cracked

Prestressed concrete

• Rebar placed under tension during setting of concrete
• Release of tension after setting places concrete in a state of compression
• To fracture concrete, applied tensile stress must exceed this

compressive stress

Particle-reinforced Fiber-reinforced Structural

threaded

rod

nut

Post-tensioning – tighten nuts to place concrete under compression

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• Elastic modulus, E

c

, of composites:

-- two “rule of mixture” extremes:

Classification: Particle-Reinforced (iii)

lower limit:

E

c

V

m

E

m

V

p

E

p

upper limit:

c m m

E = V E + V

p

E

p

Particle-reinforced Fiber-reinforced Structural

Data:

Cu matrix

w/tungsten

particles

0 20 40 60 80 10 0

150

20 0

250

30 0

350

vol% tungsten

E (GPa)

(Cu)

(W)

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Classification: Fiber-Reinforced

Fibers very strong in tension

• Provide significant strength improvement

Ex: fiber-glass - continuous glass filaments in a polymer matrix

• Glass fibers

strength and stiffness

• Polymer matrix

holds fibers in place

protects fiber surfaces

transfers load to fibers

Particle-reinforced Fiber-reinforced Structural