1. Composite(복합재) Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University 1

2. Composit(복합재) Particle-reinforced Structural Fiber Reinforced
Fiber Reinforced Polymer (FRP) (섬유강화)
Particle Reinforced (입자강화)
Structure (구조강화)

3. Structural Composite - stacking sequence: e.g., 0º/90º
• Stacked and bonded fiber-reinforced sheets
- stacking sequence: e.g., 0º/90º
- benefit: balanced, in-plane stiffness
• Sandwich panels
- low density, honeycomb core
- benefit: small weight, large bending stiffness
honeycomb
adhesive layer
face sheet 3 3

4. Particle Reinforced Composites I
Spheroidite
Steel
기지:
a -페라이트
(ductile)
입자:
시맨타이트 ( Fe 3 C )
(brittle)
60 mm
WC/Co
초경공구
기지:
코발트
(ductile)
입자:
텅스텐
(brittle,
hard) V m :
10-15 vol%!
600 mm
자동차타이어
Carbon black
기지: 고무
(compliant)
입자: 탄소
(stiffer)
0.75 mm 4

5. Particle Reinforced Composites II
Concrete : 자갈 + 모래 + 시맨트
Reinforced(강화) Concrete : 철근을 넣고 콘크리트를 부어 인장 응력에 견딜 수 있는 능력을 향상
Prestress Concrete : 철근에 인장 응력을 가한 상태로 콘크리트를 부어 경화시킨 다음 인장 응력을 제거.
Post tensioning : Place the tendons and nail anchors to the formwork, cast the concrete slab, remove the formwork, stress and anchor the tendons, then cut and grout the tendons with non-shrink grout. 5 5

6. Particle Reinforced Composites III
• Elastic modulus, Ec, of composites:
- two approaches. c m
upper
limit: E = V + p
“rule of mixtures”
Data:
Cu matrix
w/tungsten
particles 20 4 6 8 10
150
250 30
350
vol% tungsten
E(GPa)
(Cu) ( W)
lower limit: 1 E c = V m + p
• Other Characteristics:
- Electric resistance, R: Replace E in equations with R.
- Thermal conductivity, k: Replace E in equations with k. 6

7. Fiber Reinforced Polymer (FRP)
FRP (복합재료) Fiber(섬유) + Plastic matrix (모재)
Fiber: Kevlar, Glass fiber, Graphite fiber, Boron
Plastic matrix: Epoxy, Polyester
Process
Impregnation: fiber+resin
Molding
Cure by heat & pressure

8. Fiber Reinforced Polymer, FRP
Composites are made from two (fiber + plastic matrix) or more materials with significantly different properties and which remain separate on a macroscopic level.
Reinforcements (fiber) improve strength, stiffness of plastic matrix.

9. Composite Usage
Bow wings, tennis rackets, racing bicycles and skis are made of [Glass, Carbon fiber] + [Epoxy matrix]  composit.

10. Fiber materials
Fibers are strong, stiff, have a high specific strength and specific modulus.
But they are brittle, abrasive and lack toughness
Ex) Kevlar, Glass fiber, Graphite fiber, Boron.
stiffness/density
strength/density
Steel, Aluminum
Glass fiber
Kevilar
Graphite
Boron

11. Kevlar (Polymer fiber)
Kevlar is a light, strong para-aramid synthetic fiber.
Kevlar has many applications such as racing tires, because of its high tensile strength-to-weight ratio; 5 times stronger than steel on an equal weight basis.
Kevlar(yellow)+Graphite(black)
Bulletproof helmet & vest

12. Glass fibers (유리섬유) Glass fiber is chipper than others.
Called Glass-fiber reinforced polymer (GFRP).
Glass fiber
Fishing bloat

13. Graphite fibers (탄소섬유)
Graphite fibres are more expensive; low density, high strength, and high stiffness.
Called carbon-fiber reinforced polymer(CFRP).
Boing787

14. Boron fibers
High strength and stiffness in tension, compression and resistant to high temperatures.
High density
Expensive
made with carbon and boron fibre

15. Plastic matrix Matrix (Resin) in reinforced plastics has 3 functions:
Transfer the stress to the fibres
Protect fibres against physical damage.
Reduce propagation of cracks in the composite.
Epoxy(80%), Polyester (cheap).
Carbon fiber + Epoxy

16. Metal matrix
The advantage is it has higher resistance to elevated temperatures and higher ductility and toughness.
Limitations are that it has higher density and makes processing more difficult.
Fiber
Matrix
Application
Graphite
Aluminum
Helicopter, Tennis racket
Magnesium
Satellite
Boron
Compressor blade
Titanium
Jet-engine fan blade

17. Properties of Fiber reinforced plastics
Type and length of the fibres.
Volume fraction of the reinforcement.

18. Properties of Fiber reinforced plastics
The highest stiffness and strength is obtained when fibres are aligned in the direction of tension force.