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Learning Objectives:Learning Objectives:

• What are composites made of?• How are composites fabricated?• Composite Material Properties

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Examples of Composite Members: Concrete slab reinforced with steelCarbon fiber and plastic snow skisKevlar and fiberglass boatsConcrete slab on a metal deck

.

concrete

corrugated metal deck

IntroductionIntroduction

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IntroductionIntroduction

Composite materials consist of two components: the fiber and the matrix

1. Fiber – the load carrying material

2. Matrix - the fluid binder that hold the fibers in place when it solidifies.

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Fibers Materials:Fibers Materials:

1. Glass fiber (hence, fiberglass)

2. Aramid fiber (Kevlar)

3. Graphite fiber (carbon)

4. Metal fiber (concrete, ceramics)

5. Boron fiber

6. Wood fiber

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Fibers Forms:Fibers Forms:

• Strands (roving) – typically used with mandrel . Direction and spacing controlled

• Woven mesh in sheets. Direction controlled

• Chopped fiber (approx 1” long) – random direction

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Back to airplane wing

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Stresses in Beams

A.) Bending Stresses

1.) Introduction

When a beam is subjected to positive bending moment, the top shortens and the bottom lengthens.

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The bending strains are zero at the neutral axis.

The bending strains increase proportionately with the distance from the neutral axis.

The maximum strains occur at the top and bottom of the beam (outer fibers)

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Since stress is directly related to strain

= E), bending stress is also zero at the neutral axis and increases with the distance from the neutral axis.

The maximum bending stresses occur at the top and bottom of the beam (outer fibers)

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2.) Maximum Bending Stress

b,max = Mc I

b,max = Maximum bending stress at a given cross-section (ksi).

c = Distance from N.A. to the outer fibers of cross-section (in)

M, I = as defined before.

N.A.ctop

cbot

y

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3.) Strong Axis vs. Weak Axis

Strong Axis

N.A.

Weak Axis

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B.) Shear Stress - Average Web Shear

v= V_

dtw

d twd

tw d

tw