bmcb 4463 chapter 1 introduction to composite materials

SITI HAJAR SHEIKH MD FADZULLAH hajar@utem.edu.my

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ITEM CRITERIA PRECENTAGE

(%) COURSE WORK

MID SEMESTER EXAMINATION

1.5 hour (w7/w9) 20

ASSIGNMENT, REPORT AND QUIZ

Group Assignment a. Group Assignment b. Individual Assignment c. 2 Quiz

10 10 10

FINAL EXAMINATION

EXAM 2.5 – 3.0 hours

50

TOTAL 100

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Week Chapter Remarks

1 CHAPTER 1: Introduction to Composites CHAPTER 2 :Introduction to Advanced Materials

2&3 CHAPTER 3 :Basic Constituents Materials in Composites

Quiz 1

4 CHAPTER 4: Manufacturing Processes

5 CHAPTER 5 : Properties and Applications of FRP

6& 7 CHAPTER 6: Nanomaterials

8 MID SEMESTER BREAK

9&10 CHAPTER 7 :Biomaterials

Individual Assignment

11&12 CHAPTER 8 : Electric and Magnetic Materials

13 CHAPTER 9 :Refractory Materials

Quiz 2

14 CHAPTER 10: Surface Engineering

15 CHAPTER 11: Powder Metallurgy

Group Assignment

Note :W7/W9: Mid Semester Exam (20%)

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The idea of composite materials is not a new or recent one. Nature is full of examples wherein the idea of composite

materials is used. The coconut palm leaf, for example, is essentially a

cantilever using the concept of fiber reinforcement. Wood is a fibrous composite: cellulose fibers in a lignin

matrix. The cellulose fibers have high tensile strength but are very flexible (i.e., low stiffness), while the lignin matrix joins the fibers and furnishes the stiffness.

Bone is yet another example of a natural composite that supports the weight of various members of the body. It consists of short and soft collagen fibers embedded in a mineral matrix called apatite.

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Human bone

Hard wood

Coconut leaf

A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macro-scale.

Normally, the components can be physically identified and exhibit an interface between one another.

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MATRIX +REINFORCEMENT =COMPOSITES

Based on matrix materials: - PMC,MMC,CMC Function : electrical etc. Geometry of reinforcements: - Particle reinforced, Fibre reinforced, structural.

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Composites

Polymer Matrix Material (PMC)

Thermoplastic (T/P)

Thermoset

Crystalline Non-crystalline

(Amorphous)

Rubber

Metal Matrix Material (MMC)

Ceramic Matrix Material (CMC)

PMC : The most common matrix materials are polymeric. Reasons: ease of processing (need not high pressures and high temperatures) The main disadvantages: Low working temperatures, high coefficient of thermal expansion, dimensional instability and sensitivity to moisture and radiation.

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MMC: In comparison to PMC, MMC have higher transverse strength and stiffness, greater shear and compressive strengths and better high temperature capabilities, non-inflammable, high electrical and thermal conductivities and resistance to radiations.

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CMC: One of the main reasons to produce CMC is to increase the toughness. Examples of materials: alumina and silicon carbide. Problems/issues with CMC: The processing is more complex, therefore the improvement in toughness is associated with an extra cost burden. 12

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Particulate reinforcements: have dimensions that are equal in all directions, with the shape being either spherical, cubic, platelet or any regular or irregular geometry; with the orientation either random or with preferred orientation.

A fibrous reinforcement is characterized by its length being much greater than its cross-sectional dimension, known as the aspect ratio.

In single layer composites, long fibres with high aspect ratio are called continuous fibre reinforced composites; whilst the discontinuous fibre composites are fabricated using short fibres of low aspect ratio.

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The frequently encountered preferred orientation in the case of a continuous fibre composite is termed unidirectional and the corresponding random situation can be approximated to by bidirectional woven reinforcement.

Multilayered composites are another category of FRP, classified either as laminates or hybrids.

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(a) Longitudinal direction

(b) Transverse direction

(c )Through-thickness direction

Laminates are sheet constructions which are made by stacking layers/plies or laminae and usually unidirectional in a specific sequence.

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(a) Tapes containing aligned fibers can be joined to produce a multi-layered different orientations to produce a quasi-isotropic composite. In this case, a 0°/+45°/90° composite is formed.

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(a) Typical example of a honeycomb core sandwich panel, consisting of two layers of face-sheet, sandwiched between the core in the form of a honeycomb core, with the application of adhesive layers in between.

(b) The fabricated sandwich panel

(a) (b)

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Hybrids are usually multilayered composites with mixed fibres and are becoming commonplace. The fibres maybe mixed in a ply or layer by layer and these composites are designed to benefit from the different properties of the fibres employed.

An example of this is a mixture of glass and carbon fibres incorporated into a polymer matrix gives a relatively inexpensive composite, owing to the low cost of the glass fibres, but with mechanical properties enhanced by the excellent stiffness of carbon. Some hybrids have a mixture of fibrous and particulate reinforcement.

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is the constituent that is continuous and is often but not always, present on the greater quantity in the composite.

is the properties of the matrix that are improved by incorporating another constituent to produce a composite.

Matrix material may be based on ceramic, metallic or polymeric material.

Typically, polymers have low strength and Young’s Moduli, ceramic are strong, stiff and brittle and metals have intermediate strengths and moduli together with good ductility i.e. they are not brittle.

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is the second constituent in a composite system, usually referred to as the reinforcing phase or reinforcement, since it enhances or reinforces the mechanical properties of the matrix.

In most cases, the reinforcement is harder, stronger and stiffer than the matrix, with some exceptions; i.e. ductile metal reinforcement in a ceramic matrix or rubberlike reinforcement in brittle polymer matrix.

The reinforcement is usually describe as being either fibrous or particulate.

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The fabrication and properties of composites are strongly influenced by the proportions and properties of the matrix and the reinforcements.

The proportions can be expressed either via the weight fraction (w), relevant to fabrication, or via the volume fraction (v), which is commonly used in the property calculation.

The definitions of w and v are related simply to the ratio of weight (W) or volume (V) as shown as follows:- 25

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𝑣𝑓 = 𝑉𝑓

𝑉𝑐

Volume fractions

And 𝑣𝑚 = 𝑉𝑚𝑉𝑐

Weight fractions

𝑤𝑓 = 𝑊𝑓

𝑊𝑐

And 𝑤𝑚 =

𝑊𝑚𝑊𝑐

Where the subscripts m, f, and c refer to the matrix, fibre (or reinforcement) and composites respectively.

We note that

𝑣𝑓 + 𝑣𝑚 = 1 And

𝑤𝑓 + 𝑤𝑚 = 1

𝑊𝑐 = 𝑊𝑓 + 𝑊𝑚

As 𝑊= ρ V, 𝜌𝑐𝑉𝑐 = 𝜌𝑓𝑣𝑓 + 𝜌𝑚𝑣𝑚

Law of Mixtures

Or 𝜌𝑐 = 𝜌𝑓

𝑉𝑓𝑉𝑐 +𝜌𝑚

𝑉𝑚𝑉𝑐

= 𝜌𝑓 𝑣𝑓 + 𝜌𝑚𝑣𝑚

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It may be shown that

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𝜌𝑐=𝑤𝑓

𝜌𝑓+ 𝑤𝑚𝜌𝑚

Also,

𝑤𝑓 = 𝑊𝑓

𝑊𝑐=

𝜌𝑓𝑉𝑓

𝜌𝑐𝑉𝑐 =

𝜌𝑓

𝜌𝑐 𝑣𝑓

Similarly,

𝑤𝑚 =𝑊𝑚𝑊𝑐

=𝜌𝑚𝑉𝑚𝜌𝑐𝑣𝑐

=𝜌𝑚𝜌𝑐𝑣𝑚

Therefore, a generalized form of the equation is

𝑋𝑐 = 𝑋𝑚𝑣𝑚 + 𝑋𝑓𝑣𝑓

Where 𝑋𝑐 represents an appropriate property of the composite, known as the Law of Mixtures.

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A unidirectional composite is composed of 65% by volume of carbon fibres (modulus 240 GPa) in an epoxy resin matrix (modulus 4GPa). Calculate the longitudinal modulus of the composite. Using the Rule of Mixtures,

𝐸11 = 𝐸𝑓𝜐𝑓 + 𝐸𝑚𝜐𝑚

Here, 𝜐𝑓= 0.65 and hence 𝜐𝑚=0.35,

𝐸11 = 0.65x240 + ( 0.35x4)

= 156 + 1.4

= 157.4 GPa

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Compare the longitudinal and transverse stiffness of two composites with the same matrix but different fibres. In the first case, Ef/Em=50 and in the second case, Ef/Em = 25. Take 𝜐𝑓= 0.50 .

𝐸11 = 𝐸𝑓𝜐𝑓 + 𝐸𝑚𝜐𝑚

Now,

Or

𝐸11𝐸𝑚

=𝐸𝑓

𝐸𝑚𝜐𝑓 + 𝜐𝑚

Also, 1

𝐸22=𝜐𝑓

𝐸𝑓+𝜐𝑚𝐸𝑚

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Or,

𝐸𝑚𝐸22

=𝜐𝑓

𝐸𝑓𝐸𝑚

+ 𝜐𝑚

For 𝐸11𝐸𝑚

= 0.5x 0.5 + 0.5 = 25.5,

𝐸𝑚𝐸22

=0.5

50+ 0.5 =

25.5

50,

Or

𝐸22𝐸𝑚

=0.5

25+ 0.5 =

13

25

𝐸22𝐸𝑚

= 1.92

Also,

𝐸11𝐸𝑚

=13.0

1.92= 6.77

So, we can see here that for this volume fraction, changing the fibre to one with double the modulus results in a doubling of the composite’s longitudinal Modulus, but in only about 2% increase in the composite’s transverse modulus.

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Effect of fiber orientation on the tensile strength of E-glass fiber-reinforced epoxy composites.

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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Increasing the length of chopped E-glass fibers in an epoxy matrix increases the strength of the composite. In this example, the volume fraction of glass fibers is about 0.5.

Improved properties (thermal, mechanical, electrical, etc.)

Example: PMCs vs. metals: low density,ρ. Therefore, higher specific modulus, (E/ ρ) and specific

strength; reduced weight leading to greater energy efficiency (transport) and cost savings.

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Matthew, F.L., and Rawling, R.D., (2003). Composite Materials: Engineering and Science, Woodhead Publishing Limited. -Chapter 1: Overview- pg 1-28

Chawla, Krishan Kumar. Composite materials: Science and Engineering. Springer, 2012.- Chapter 1 : Introduction- pg 1-4

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