Composites I / Objectives

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Composites I / Objectives

• Name the phases present in a composite material.

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Composites I / Objectives

• Name the phases present in a composite material.
• Identify composite materials based on matrix
  type, reinforcement form, or arrangement.

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Composites II

• Composites Properties
• Volume Fractions
• V f V m Vv 1
• Fiber Matrix Void

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Composites II

• Composites Properties
• Volume Fractions
• V f V m V v 1
• Fiber Matrix Void
• Mass Fractions
• mf mm 1

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Composite Density

• ? M ?f V f ?m V m
• V V
• ?f V f ?m V m
• V V
• ?f V f ?m V m

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Composite Density

• ? M ?f V f ?m V m
• V V
• ?f V f ?m V m
• V V
• ?f V f ?m V m
• OR ? ?f V f ?m(1- V f)

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• In terms of mass fraction - can find void volume
• ? 1
• mf mm V v
• ?f ?m ?
• Vv 1 - ? ( mf mm )
• ?f ?m

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• Common Analysis
• Two results
• -Volume fraction fibers
• -Void fraction

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• Mechanical Properties
• Anisotropic!
• Think Series and Parallel

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• X-Direction
• Parallel Properties
• FTOTAL FFIBER FMATRIX
• ?TOTAL ?FIBER ?MATRIX

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• Y Z Directions
• Series Properties
• FFIBER FMATRIX FAPPLIED
• ?TOTAL ?FIBER ?MATRIX

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• Longitudinal Modulus
• Fl Fm Ff

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• Fc Fm Ff
• ?cAc ?mAm ?fAf
• ?c ?mAm ?fAf
• Ac Ac
• ?c lc ?mAm lc ?fAf lc
• lc Ac lc Ac lc
• ?c ?m V m ?f V f
• V c V c

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• Longitudinal E
• ?c ?mV m ?fV f
• Since ?c ?m ?f
• ?c ?mV m ?fV f
• ?c ?m ?f
• Hookes Law Ec EmV m E fV f

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• Transverse E
• Similarly 1 V m V f
• Ec Em Ef
• OR Ec Em Ef
• (1- V f) Ef V f Em
• ? Rule of Mixtures

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Design Difficulties with Composites

• Joining
• Bond is better
• Fasteners can be a problem
• Joints can cancel advantages of CMs

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Design Difficulties with Composites

• Free Edges
• Delamination stresses at edges
• Exposure of fibers to environment

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Design Difficulties with Composites

• Damage Tolerance/Delamination Tendency
• Transverse loading can cause delamination
• Laminated composites prone to delamination
• Impact Damage is a special problem

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What is the theoretical maximum possible volume
fraction of long fibers in a composite?

• Hint

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This Is Not Practical

• Perfect packing unlikely
• Fiber Waviness
• Fibers shouldnt touch
• Commonly Vf is 0.5 to 0.7

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Crack stopping in composites
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Anisotropy in Strength
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Anisotropy in Crack Growth
Delamination or Longitudinal Crack