Study different categories of composites: particulate, fiber, and …contents.kocw.net/KOCW/document/2014/Pusan/joyeongrae/5.pdf · 2016-09-09 · Fiber-Reinforced Composites (섬유강화

Pusan National University Department of Materials Science& Engineering

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

Chapter 16. Composites (Teamwork and Synergy in Materials)


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?



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



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%).

Laminar ⇒ Veneer 합판

Fiber ⇒ 철근

Particulate ⇒ 콘크리트



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.

Section 16.1 Dispersion-Strengthened Composites

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

⇒ 분산강화상과 입자강화상의 차이: 입자 크기?, 산화물?



Figure 16.2 Comparison of the yield strength of dispersion-strengthened 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




Matrix

분산상의 요구조건?


Figure 16.3 Electron micrograph of TD-nickel. The dispersed ThO2 particles have a diameter of 300 nm or less (× 2000)

Nickel 모상에 ThO2가 분산됨.



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:

Example 16.1 TD-Nickel Composite



Example 16.1 SOLUTION (Continued)

Therefore, there is 0.0184 cm3 of ThO2 per cm3 of composite. The volume of each ThO2 sphere is:



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.



Figure 16.4

Microstructure of tungsten carbide—20% cobalt-cemented carbide (x1300).

WC



Infiltration ⇒ 모세관 현상 고융점 분말 틀에 저융점 액상 침투



Figure 16.6 The effect of clay on the properties of polyethylene.

Extenders to stiffen the polymer : 가장 경제적인 복합재료 설계



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 fiber-reinforced 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



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.

only if the fibers are continuous and unidirectional.



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:

Example 참조.

f

f

m

m

C Ef

Ef

E+=

⊥,

1



Section 16.4 Characteristics of Fiber-Reinforced

Composites

Many factors must be considered when designing a fiber-reinforced 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 fiber-reinforced composite.

설계시 유의사항: (섬유의 길이, 직경, 방향, 양 및 특성), (기지상의 특성), (섬유와 기지상의 결합력)



Figure 16.11 Effect of fiber orientation on the tensile strength of E-glass fiber-reinforced epoxy composites.

응력이 섬유 축에 대해 직각으로 작용할 때와 평행하게 작용할 때에 대한 섬유강화 복합재료의 탄성계수 유도 예제 16-5, 예제 16-6 참고



The properties of Fiber-reinforced composites can be tailored to meet different types of loading conditions:






(강화재)



Figure 16.14 Comparison of the specific strength and specific modulus of fibers versus metals and polymers.



Section 16.5 Manufacturing Fibers and Composites

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.

Making the Fiber Arranging the Fiber Producing the Composite


















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.

복합재료의 파괴 방지법: 두 재료 사이의 큰 본딩력과 작은 열팽창 계수차이

** CFRP or GFRP: carbon(glass)-fiber reinforced plastics 미래 유망재료

** FRP??





* 방탄복용 아라미드 섬유

*



Unfortunately, the polymer fibers lose their strength

at relatively low temp.



Nb3Sn has good super- conducting properties

but is very brittle.



C-C composites are stronger at high temp.





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).

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.



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.





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 higher-strength 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.





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.





발표자

프레젠테이션 노트

Corrugation: 물결 주름



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.

Documents

Study different categories of composites: particulate, fiber, and …contents.kocw.net/KOCW/document/2014/Pusan/joyeongrae/5.pdf · 2016-09-09 · Fiber-Reinforced Composites (섬유강화