Transcript Chapter 16. Composites (Teamwork and Synergy in Materials)

Chapter 16. Composites (Teamwork and Synergy in Materials)
Objectives of Chapter 16
Study different categories of composites:
particulate, fiber, and laminar
Focus on composites used in structural or
mechanical applications.
 Composites(복합재료):
원재료로 얻을 수 없는 특성(예: 강도, 내부식성, 고온특성 등)을 얻기 위하여
2가지 이상의 물질을 접합 혹은 특성 결합시켜 얻은 물질  콘크리트, 합판 등
 복합재료의 형태적 분류
Particulate composites(입자 복합재료): 산화물입자, 고경도입자
Fiber-reinforced composites(섬유강화 복합재료): 유리파이버, 철근
Laminar composites(층상 복합재료): 합판, 클래딩, 적층재
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Have you ever wondered?

What are some of the naturally occurring composites?

Why is abalone shell, made primarily of calcium carbonate, so
much stronger than chalk, which is also made of calcium
carbonate?

What sporting gear applications make use of composites?

Why are composites finding increased uses in aircrafts and
automobiles?
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Chapter Outline
16.1 Dispersion-Strengthened Composites
16.2 Particulate Composites
16.3 Fiber-Reinforced Composites
16.4 Characteristics of Fiber-Reinforced Composites
16.5 Manufacturing Fibers and Composites
16.6 Fiber-Reinforced Systems and Applications
16.7 Laminar Composite Materials
16.8 Examples and Applications of Laminar Composites
16.9 Sandwich Structures
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Laminar
⇒ Veneer 합판
Fiber
⇒ 철근
Particulate
⇒ 콘크리트
Figure 16.1 Some examples of composite materials: (a) plywood is a laminar
composite of layers of wood veneer, (b) fiberglass is a fiber-reinforced composite
containing stiff, strong glass fibers in a softer polymer matrix ( 175), and (c)
concrete is a particulate composite containing coarse sand or gravel in a cement
matrix (reduced 50%).
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Section 16.1
Dispersion-Strengthened Composites
⇒ 분산강화상과 입자강화상의 차이: 입자 크기?, 산화물?
 A special group of dispersion-strengthened nanocomposite
materials containing particles 10 to 250 nm in diameter is
classified as particulate composites.
 Dispersoids - tiny oxide particles formed in a metal matrix that
interfere with dislocation movement and provide strengthening,
even at elevated temperatures.
 The particulate composites contain large amounts of coarse
particles that do not block slip effectively.
Dispersoid(분산상)은 입자형상을 가지며, 고온에서도 강도가 높아야 함.
대신에 matrix(기지상, 연속상)는 연하고 충격을 흡수할 수 있도록 설계함.
⇒ 따라서 분산상은 강도 유지 기능, 기지상은 충격 흡수 기능을 가짐
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Figure 16.2
Comparison of the yield
strength of dispersionstrengthened sintered
aluminum powder (SAP)
composite with that of two
conventional two-phase
high-strength aluminum
alloys.
The composite has
benefits above about
300°C. A fiber-reinforced
aluminum composite is
shown for comparison.
온도증가에 따른 강도저하 경향
Matrix(모재): Al
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Matrix
분산상의 요구조건?
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Nickel 모상에
ThO2가 분산됨.
Figure 16.3 Electron micrograph of TD-nickel.
The dispersed ThO2 particles have a diameter
of 300 nm or less ( 2000)
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Example 16.1
TD-Nickel Composite
Suppose 2 wt% ThO2 is added to nickel. Each ThO2 particle
has a diameter of 1,000 Å. How many particles are present
in each cubic centimeter?
⇒ 기지 혹은 모재에 존재하는 분산상의 갯수?
Example 16.1 SOLUTION
The densities of ThO2 and nickel are 9.69 and 8.9 g/cm3,
respectively. The volume fraction is:
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Example 16.1 SOLUTION (Continued)
Therefore, there is 0.0184 cm3 of ThO2 per cm3 of
composite. The volume of each ThO2 sphere is:
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Section 16.2
Particulate Composites
 Rule of mixtures(혼합법칙) - The statement that the
properties of a composite material are a function of the
volume fraction of each material in the composite.
 Cemented carbides(초경합금) - Particulate composites
containing hard ceramic particles bonded with a soft metallic
matrix.
 Electrical Contacts(전기접점) - Materials used for electrical
contacts in switches and relays must have a good
combination of wear resistance and electrical conductivity.
 Polymers(폴리머) - Many engineering polymers that contain
fillers and extenders are particulate composites.
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WC
Figure 16.4
Microstructure of tungsten carbide—20%
cobalt-cemented carbide (x1300).
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 Infiltration ⇒ 모세관 현상
 고융점 분말 틀에 저융점 액상 침투
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Extenders to stiffen
the polymer :
가장 경제적인 복합재료 설계
Figure 16.6 The effect of clay on the properties of polyethylene.
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Section 16.3
Fiber-Reinforced Composites
(섬유강화 복합재료)
 The Rule of Mixtures in Fiber-Reinforced Composites(밀도)
 Strength of Composites - The tensile strength of a fiberreinforced composite (TSc) depends on the bonding
between the fibers and the matrix (adhesion bet. f and m)
 기지상의 역할: 섬유의 지지, 하중의 전달, 섬유의 손상보호 및 환경적 보호
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only if the fibers are
continuous and unidirectional.
Figure 16.8 The stress-strain curve for a fiber-reinforced composite.
At low stresses (region l), the modulus of elasticity is given by the
rule of mixtures. At higher stresses (region ll), the matrix deforms
and the rule of mixtures is no longer obeyed.
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 When the load is applied perpendicular to the fibers, each
component of the composite acts independently of the
other. The modulus of the composite is:
fm f f
1


EC , Em E f
 Example 참조.
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Section 16.4
Characteristics of Fiber-Reinforced
Composites
 Many factors must be considered when designing a fiberreinforced composite, including the length, diameter,
orientation, amount, and properties of the fibers; the
properties of the matrix; and the bonding between the
fibers and the matrix.
 Aspect ratio(종횡비) - The length of a fiber divided by its
diameter (l / d).
 Delamination - Separation of individual plies of a fiberreinforced composite.
 설계시 유의사항:
(섬유의 길이, 직경, 방향, 양 및 특성), (기지상의 특성), (섬유와 기지상의 결합력)
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응력이 섬유 축에 대해
직각으로 작용할 때와
평행하게 작용할 때에 대한
섬유강화 복합재료의 탄성계수 유도
 예제 16-5, 예제 16-6 참고
Figure 16.11
Effect of fiber orientation
on the tensile strength of
E-glass fiber-reinforced
epoxy composites.
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The properties of Fiber-reinforced composites can be
tailored to meet different types of loading conditions:
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(강화재)
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Figure 16.14
Comparison of the
specific strength and
specific modulus of
fibers versus metals
and polymers.
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Section 16.5
Manufacturing Fibers and Composites
Making the Fiber
Arranging the Fiber
Producing the Composite
 Chemical Vapor Deposition (CVD: 화학기상증착법) Method for manufacturing materials by condensing the
material from a vapor onto a solid substrate.
 Carbonizing (탄화) - Driving off the non-carbon atoms
from a polymer fiber, leaving behind a carbon fiber of
high strength. Also known as pyrolizing.
 Filament winding (필라멘트감기) - Process for producing
fiber-reinforced composites in which continuous fibers
are wrapped around a form or mandrel.
 Pultrusion(인발성형) - A method for producing
composites containing mats or continuous fibers.
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Making the Fiber
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Arranging the Fiber
Producing the Composite
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Making the Fiber
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Arranging the Fiber
Producing the Composite
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Making the Fiber
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Arranging the Fiber
Producing the Composite
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Making the Fiber
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Arranging the Fiber
Producing the Composite
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Making the Fiber
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Arranging the Fiber
Producing the Composite
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** FRP??
Section 16.6
Fiber-Reinforced Systems and Applications
 Polymer-Matrix Composite (PMC, 폴리머기지상 복합재료)
-Reinforced with high-strength polymer, metal, or
ceramic fibers.
 Metal-Matrix Composites (MMC, 금속기지상 복합재료)
- These materials, strengthened by metal or ceramic
fibers, provide high-temperature resistance.
 Ceramic-Matrix Composites (CMC, 세라믹기지상 복합재료)
- Composites containing ceramic fibers in a ceramic
matrix are also finding applications.
** CFRP or GFRP: carbon(glass)-fiber reinforced plastics  미래 유망재료
 복합재료의 파괴 방지법: 두 재료 사이의 큰 본딩력과 작은 열팽창 계수차이
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*
* 방탄복용 아라미드 섬유
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Unfortunately, the polymer fibers
lose their strength
at relatively low temp.
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Nb3Sn has good superconducting properties
but is very brittle.
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C-C composites are
stronger at high temp.
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Crack propagates around the fiber.
Poor bonding begins the fiber to pull out of the matrix.
Unbroken fibers bridge the crack.
A compressive stress keeps the crack from opening.
Figure 16.29 Two failure modes in ceramic-ceramic composites:
(a) Extensive pull-out of SiC fibers in a glass matrix provides good composite
toughness (x20).
(b) Bridging of some fibers across a crack enhances the toughness of
a ceramic-matrix composite (unknown magnification).
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Section 16.7
Laminar Composite Materials
(층상복합재료)
 Rule of Mixtures - Some properties of the laminar
composite materials parallel to the lamellae are
estimated from the rule of mixtures.
 Corrosion and wear resistance depend primarily on only
one of the components of the composite, so the rule of
mixtures is not applicable.
 Producing Laminar Composites - (a) roll bonding, (b)
explosive bonding, (c) coextrusion, and (d) brazing.
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Chapter 16. Composites (Teamwork and Synergy in Materials)
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Section 16.8
Examples and Applications of
Laminar Composites
 Laminates - Laminates are layers of materials joined by
an organic adhesive.
 Cladding(클래딩) - A laminar composite produced when a
corrosion-resistant or high-hardness layer of a laminar
composite formed onto a less expensive or higherstrength backing.
 Bimetallics - A laminar composite material produced by
joining two strips of metal with different thermal
expansion coefficients, making the material sensitive to
temperature changes.
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Chapter 16. Composites (Teamwork and Synergy in Materials)
Section 16.9
Sandwich Structures
(비강도의 중요성 ⇒ 구조)
 Sandwich (샌드위치)- A composite material constructed
of a lightweight, low-density material surrounded by
dense, solid layers. The sandwich combines overall light
weight with excellent stiffness.
 Honeycomb (벌집구조) - A lightweight but stiff assembly
of aluminum strip joined and expanded to form the core
of a sandwich structure.
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Chapter 16. Composites (Teamwork and Synergy in Materials)
요약을 위한 숙제
1. 복합재료(composites)를 정의하고 특징에 대하여 논하시오.
2. 복합재료를 강화재의 모양에 따라 3가지로 구분해서 특징에
대하여 설명하시오. 또한 실제 예를 2가지씩 들어보세요.
3. 섬유강화 복합재료(fiber-reinforced composites) 에서
섬유상과 기지상의 요구조건과 역할에 대하여 논하시오.
4. 복합재료에서 혼합법칙(rule of mixtures)에 대하여 설명하시오.
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