Transcript Environmental Degradation of Materials

Subject: Composite Materials
Science and Engineering
Subject code: 0210080060
Prof. C H XU
School of Materials Science and Engineering
Henan University of Science and Technology
Chapter 1: Overview of composite materials
Information
 Myself:


Name: Chun Hua XU
Contact methods:
 E-mail: [email protected]
Information
Lecture:
Bilingual lectures (both English and
Chinese)
Tutorial & class discussion: Last 5-10 min of normal lectures
Office hours & location:
Building 1, room 305;
Friday 16:30~17:30
Assessment Methods:
10% from attended class
10% from homeworks
10% from experiment
70% from final examination
Information
Teaching Plan
Weeks
1
Contents
Overview of Composite Materials
2-3
Matrix and Reinforcements:
4-6
Composite Materials:
Metal Matrix Composite
Polymer Matrix Composite (lecture and video show)
Ceramics Matrix Composite
11
Properties of Composite Materials
12
Experiment and Final Examination
Information
Text Book:
1.
Composite Materials: Engineering and Science
F. L. Matthews and R. D. Rawlings, CRC Press, 2000
Reference Books:
1.
2.
3.
Foundations of Materials Science and Engineering, W. F. Smith,
McGraw-Hill, Inc., 1993
Engineering Materials: Properties and Selection, K. G. Budinski,
Prentice Hall, 1992
Introduction to Materials (材料概论), Z. H. Shui, Wuhan University
of Technology Press, 2005
Other References:
1.
2.
3.
Lecture notes
Video study guide
Experimental guide
Objectives of the subject
 Basic knowledge on composite materials
 The relationship between the structures and
the properties of composite materials
 Ability of reading scientific papers on materials
field in English
Chapter 1:
Overview of composite materials
 Introduction to composite materials
 Definitions and classification
 Applications
 Structures of materials
 Atomic structure and bonding in solids
 Crystalline & non-crystalline structures
 Microstructure
 Defects in crystalline solids
 Point defects
 Line defects
 Face defects
Introduction to composite materials
Classification of materials
 Engineering Materials:
 Metal and alloy: e.g. Cu, steels
 Ceramics: metallic-nonmetallic compound, e.g. Al2O3
 Polymer: Organic compounds, containing C, H, O, N, Si,
e.g. polyethylene
 Composites: combination of materials, e.g. glass fibers
(strength) in polymer (flexibility)
 Advanced materials:
 Semiconductors: e.g. Si, GaN
 Functional materials: e.g. shape memory alloy, the change
in shape with temperature
 Nano-materials: at least one dimension of materials in
nano-scale.
Introduction to composite materials
Classification of materials
Basic properties of engineering materials
property
elements
METALS
met. elements
or plus little non-metals
POLYMERS
CERAMICS
C,H,O,S, N, Si, F, Cl
Metal+non-metal
(C,N,O, P, S)
strong
strength
strong
strong - intrachain
weak - interchain
density
varies (high)
low
Less than metal
fracture
ductile (malleable)
ductile
brittle
poor
poor
elect. cond.
excellent
therm. cond.
excellent
poor
poor
chem. react.
varies (high)
moderate
low
transparence
opacity
Introduction to composite materials
Classification of materials
Continuing quest for
improving performance:
 Less weight,
 more strength
 lower cost
 Composites:
combination of
materials, e.g. glass
fibers (strength) in
polymer (flexibility)
Metals
Polymers
Ceramics
Introduction to composite materials
Definition of Composite Materials
A composite:
 a solid material has two or more distinct
constituents (要素, 物质) or phases
 composite properties are different from the
properties of constituents
 Synthetic composites: composite produced by
intimately mixing and combining the constituents
by various means
Introduction to composite materials
Definition of Composite Materials
 (a) Non-Composite: micrograph of a steel with 0.45wt%C (ferrite
and pearlite microstructure)
 (b) Synthetic-Composite: SEM of an Al alloy reinforced with SiC
particles
Introduction to composite materials
Definition of Composite Materials
 In nature:
 a palm leaf, cellulose (纤维素） fibers in a lignin （木质素）
matrix (wood),
 Composite Examples
 adding straw to mud for building stronger mud walls,
 carbon black in rubber,
 steel rods in concrete,
 cement mixed with sand,
 fiberglass in resin etc.
Introduction to composite materials
Classification of composite materials
Components of Composite Materials
The matrix (continuous):
polymers
metals
ceramics
The distributed phase or reinforcement:
particles,
whiskers or short fibres, continuous fibres,
laminate.
(Polymers, metals and ceramics)
Interface between matrix and reinforcement:
Introduction to composite materials
Classification of composite materials
According to matrices
 Metallic Matrix Composites (MMCs)
 Polymer Matrix Composites (PMCs)
 Ceramic Matrix Composites (CMCs)
Introduction to composite materials
Classification of composite materials
- According to reinforcements
(a) particle, random
(b) Discontinuous fiber,
unidirectional
(c) Discontinuous, fiber,
random
(d) Continuous fibers
unidirectional
The stacking fiber-reinforced
layers for a laminar composite
Introduction to composite materials
History of composite materials
Introduction to composite materials
Classification of composite materials
The main functions of the reinforcement (fibers):
 To carry the load, about 70-90% of load is carried
by fibers.
 To provide stiffness, strength, thermal stability in
composite.
 All fibres are strong in their longitudinal direction.
The material properties perpendicular to the fibre
direction are not as good.
Introduction to composite materials
Classification of composite materials
The main functions of the matrix
 To transfer stresses to the fibres by adhesion
and/or friction across the fibre-matrix interface
when the composite is under load.
 To bind together the fibres and to protect their
surface from damages during handling,
fabrication and the service life of the composites.
 To disperse the fibres and maintain the desired
fibre orientation and spacing.
Introduction to composite materials
Markets
Main users of composites
 The aerospace industry is the largest user of composites
 Construction and civil structures is next one, such as, glasscarbon-reinforced plastics for bridges
 The automotive industry, such as seat, load floor
 The sporting goods industry, such as golf shafts, tennis rackets,
 Marine application, such as power boats
 consumer goods, such as, doors, bathtubs, table, chairs
 General Industry, such as industrial rollers and shafts
Main reason is the reduce in price, For example, carbon fiber
$150/Ib in 1970, $8/Ib in 2000
Applications in Aerospace Industry
Structures of Materials
Materials properties are determined by three levels
of structures:
 Atomic structure and bonding in solid

Arrangement of individual atoms, ions or molecules
 Crystalline & non-crystalline structures
 Orders of many atoms, ions or molecules
 Microstructure

Structural features which can be observed using optical or
electron microscope - dimensions at micro-level
Structures of Materials
Atomic structure & bonding in solids
 Atomic structure
 Bonding


Primary bonding
Second bonding
Structures of Materials
Atomic structure & bonding in solids
Atomic structure - Bohr
atomic model
Electrons revolve in
different shells;
 Each shell can only have
a certain number of
electrons;
2, 8, 18, ….
Mg
Electrons revolve around
nucleus in discrete orbits.
An orbit defines position of
an electron.
Structures of Materials
Atomic structure & bonding in solids
Valence electron
 The electrons on the outmost shell
 Participate in the bonding between atoms



If the outer shell is full, element is stable (inert gas).
If the outer shell has a couple of electrons (far from full),
then these electrons are easy to escape; (metals)
If the outer shell is almost full, then it is easy to attract
Cl
electrons; (non-metals)
Na
Ne
+10e
+11e
+17e
Atomic structure & bonding in solids
 Atoms and periodic table
Periodic table of the elements
Structures of Materials
Atomic structure & bonding in solids
Primary bonding: Metallic
bonding:
 formation of an electron sea
 Metallic bond is non-
directional.
 Metals are good conductors
because of the free
electrons.
 Metals are ductile at room
temperature, also a result of
the metallic bonding.
Structures of Materials
Atomic structure & bonding in solids
Primary bonding: Ionic bonding
 Ionic bonding: metal + nonmetal
 The attractive forces are
coulombic.
 The bonding is directional.
 Most of ceramics is ionic in
bonding.
 Characteristics of ionic solids:
 hard and brittle.
 insulative electrically and
thermally.
Na
+11e
Cl
+17e
Structures of Materials
Atomic structure & bonding in solids
Primary bonding:
Covalent bonding
 Sharing of electrons
between the two atoms
 Covalent bond is
directional.
 Covalent solids is strong
(diamond); the solids
containing covalent and
other-bond is weak
(polymer).
Structures of Materials
Atomic structure & bonding in solids
Secondary (physical, van der waals) bonding
 Permanent dipole: polar molecules  permanent
dipole moment
 Hydrogen bonding: some molecules have H.
 Exist in common molecules: H2, H2O, CH4, C6H6
 Gas, liquid or solid polymer
Structures of Materials
Atomic structure & bonding in solids
Bonding Energies and Melting Temperature
Bonding
Type
Materials
Ionic
Covalent
Bonging Energy
Melting T
kJ/mol
eV/atom
(℃)
NaCl
MgO
640
1000
3.3
5.2
801
2800
Si
C(diamond)
450
713
4.7
7.4
1410
>3550
Metallic
Al
Fe
W
324
406
849
3.4
4.2
8.8
660
1538
3410
Van der wall
Ar
Cl2
7.7
31
0.08
0.32
-189
-101
Hydrogen
NH3
H2O
35
51
0.36
0.52
-78
0
Structures of Materials
Crystalline structures
 Crystalline structures
 Amorphous
Structures of Materials
Crystalline Structures
Unit cell
 Crystalline structures: a repeating array over large
atomic distance.
 Unit cells: small repeat entities
Structures of Materials
Crystalline Structures
Crystal Systems
A unit cell:
Axial lengths of unit cell: a, b, c
Inter-axial angles: α, β, γ
Crystal system:
7 crystal systems
based on 6
parameters
Structures of Materials
Seven Crystal Systems Examples
Cubic
Diamond
Tetragonal
Wulfenite
Hexagonal
Beryl
Trigonal
Quartz
variety -amethyst
Orthorhombic
Tanzanite
Monoclinic
Gypsum
Triclinic
Montebrasite
Structures of Materials
Crystalline structures
Z
Face-centered cubic (FCC)
a
a=b=c,
a
α=β=γ=900
Y
 Cu, Al, Au, Ag…
 Coordination number: 12
 Number of atoms in a unit cell: 4
X
1
1
(8 atoms)( for corner atom)  (6 atoms)( for face atom)  4 atoms
8
2
 Atomic packing factor: 74%
Structures of Materials
Crystalline Structures
Z
a
Y
X
 Cr, Mo, Fe
(room temperature)
 2 atoms in a unit cell
 Coordination number: 8
 Atomic packing factor=0.68
Body-centered
cubic (BCC)
a=b=c,
α=β=γ=900
Structures of Materials
Crystalline Structures
Hexagonal closepacked (HCP)
 Mg, Zn, Ti …
 6 atoms in a unit cell
 Coordination number:
12
 Atomic packing factor:
0.74
a=b≠c, c/a=1.633
α=β= 900, γ=1200
Structures of Materials
Crystalline Structure: Ceramic crystal
 Crystal structure for ceramics is more complex. Example:
CaF2. Here, the Ca2+ ions are blue and the F– ions are
yellow.
 If imaging CaF2 as a group, it will be FCC structure
FCC
Noncrystalline Structures
Noncrystal: amorphous solids lack a systematic and
regular arrangement of atoms over large atomic
distances, such as glass, polymer
A crystal of silica
Silica glass
SiO2
Microstructure :
 Single crystal: periodic
arrangement of atoms
throughout the entirety of
specimens
diamond
 Polycrystal: sample is
composed by many small
crystals. Each small crystal
is called as a grain. Atoms
mismatch areas is called
as grain boundary.
Under microscope
The Defects in Crystalline Solids
 Does perfect order exist throughout crystalline
materials? No
 Defects in materials will influence the properties of
materials. e.g.


Impurity – electronic conduct of semiconductor
Dislocation defects – plastic deformation
 Crystalline defects: imperfect order in crystalline
materials



Point defects
Line defects
Face defects
Defects in Crystalline Solids
Point defects
Vacancies and
self-interstitials
 Vacancy
Missing a atom
 Self-interstitials
 An atom in the
interstitial site
 Large distortions in the
surrounding lattice
 Concentration: much
lower than that of the
vacancy

Showing a vacancy
and self-interstitial
Defects in Solids
Point defects
Impurities in solids
 Substitutional atoms
Impurity atom in normal
atom site
 Interstitial atoms
Impurity atom in
interstitial site
Showing a substitutional
and interstitial impurity
atoms two-dimensionally
Defects in Solids
Line defects: Dislocations
Edge dislocation (┴)
 Linear defect occurs at the
edge of an extra plane
 Dislocation line
 Zones of compression (top)
& of tension (bottom)
 b: Burgers vector:
Description of magnitude
and direction of the lattice
distortion

b ┴ dislocation line
Defects in Solids
Line defects: Dislocations
Screw dislocations (
)
 A spiral ramp with an
imperfection line down its
axis
 Dislocation line AB
 b // dislocation line
Top view: The screw dislocation
Defects in Solids
Face defects:
 Crystalline defects
extends in two
dimensions: grain
boundary
 Polycrystalline materials:
many crystals of various
orientations
 Grain: Individual crystals
 Grain boundary: zone
between 2 grains;
Model for grains,
Actual grains
Model for the arrangement of
atoms at grain boundary
Further Reading:
Text Book:
Composite Materials: Engineering and Science
(pages 1-10).
Reference Book:
Introduction to Materials (材料概论) pages 10-12;
21-26; 30-33
Other reference:
Lecture notes: chapter 1