mse200 - nc state universitycarbon fibers for reinforced plastics • light weight, very high...
TRANSCRIPT
Objectives/outcomes: You will learn the following:
•particle and fiber reinforcement. • Various types of fibers• Unidirectional• Rule of mixture. •Strength of fiber composites
MSE200 Lecture 20(CH. 12.1-12.3)
Composite Materials Instructor: Yuntian Zhu
Introduction
• A composite material is
• Properties of composite materials can be superior to its individual components.
• Examples:
Two types of composite materials
• Classified according to the reinforcements
– Particle reinforced composites
• Examples:
– Fiber reinforced composites
• Examples:
Glass Fibers for Reinforced Plastic Composite Materials
• Glass fiber reinforced plastic composite materials have
high strength-weight ratio, good dimensional stability,
good temperature and corrosion resistance and low
cost.
‘E’ Glass : 52-56% SiO2, + 12-16% Al2O3, 16-25%
CaO + 8-13% B2O3
Tensile strength = 3.44 GPa, E = 72.3 GPa
‘S” Glass : Used for military and aerospace
application.
65% SiO2 + 25% Al2O3 + 10% MgO
Tensile strength = 4.48 GPa, E = 85.4 GPa
Production of Glass Fibers
• Produced by drawing monofilaments from a furnace
and gathering them to form a strand.
Low cost and hence
commonly used.
http://www.google.com/search?q=glass+fiber+drawing&tbo=p&tbs=vid%3A1&source=vgc&hl=en&aq=f
Glass fiber products
http://video.google.com/videosearch?hl=en&q=glass%20fiber%20composite&gbv=2&ie=UTF-8&sa=N&tab=iv#hl=en&q=glass+fiber+composite&gbv=2&ie=UTF-8&sa=N&tab=iv&start=0
Carbon Fibers for Reinforced Plastics
• Light weight, very high strength and high stiffness.
• 7-10 micrometer in diameter.
• Produced from polyacrylonitrile (PAN) and pitch.
• Steps:
Stabilization: PAN fibers are stretched and oxidised in air
at about 2000C.
Carbonization: Stabilized carbon fibers are heated in inert
atmosphere at 1000-15000C which results in elimination of
O,H and N resulting in increase of strength.
Graphitization: Carried out at 18000C and increases
modulus of elasticity at the expense of strength
• Tensile strength = 3.1-4.45 GPa, E = 193-241 GPa,
density = 1.7-2.1 g/cc.
The highest strength: 6.9 GPa, by Toray
Carbon fiber products • http://video.google.com/videosearch?q=carbon+fiber&num=10&so=0&hl=en&start=0
Boeing 787 Dreamliner
50% structure carbon fiber composite
Aramid Fibers (Kevlar) for Reinforcing Plastic Resins
• Aramid = aromatic polyamide fibers.
• Trade name is Kevlar
Kevlar 29:- Low density, high strength, and used for ropes and cables.
Kevlar 49:- Low density, high strength and modulus and used for
aerospace and auto applications.
• Hydrogen bonds bond fiber together.
• Used where resistance to fatigue, high
strength and light weight is important.
Comparison of Mechanical Properties
• Glass fibers are cheap, for cheap civilian products
• Carbon fibers are strong but brittle, high strength structure
• Kevlar fibers are toughest, for body armor.
Matrix Materials
• Polyester and epoxy resins are the two important matrix materials.
• Polyester resins: Cheaper than epoxy resins.
Applications: Boat hulls, auto and aircraft applications.
• Epoxy resins: Good strength, low shrinkage.
Commonly used matrix materials for carbon and aramid-fiber composite.
Table 11.2
Fiberglass-polyester
Fiber Reinforced-Plastic Composite Materials
• Fiberglass-reinforced polyester resins:
Higher the wt% of glass, stronger the reinforced plastic is.
Nonparallel alignment of glass fibers reduces strength.
• Carbon fiber reinforced epoxy resins:
Carbon fiber contributes to rigidity and strength while epoxy matrix contributes to impact strength.
Polyimides, polyphenylene sulfides are also used.
Exceptional fatigue properties.
Carbon fiber epoxy material is laminated to meet strength requirements.
Rule of Mixture (isostrain condition) • Stress on composite causes uniform strain on all composite layers.
Pc = Pf + Pm
= P/A
cAc = fAf + mAm
Pc = Load on composite
Pf = Load on fibers
Pm = load on matrix
Rule of mixture of binary composites
Ec = EfVf + EmVm
c = fVf + mVm
c = fVf + mVm
Loads on Fiber and Matrix Regions
• Since = E and f = m
Pc = Pf + Pm
• From above two equations, load on each of fiber and
matrix regions can be determined if values of Ef, Em, Vf,
Vm and Pc are known.
mm
ff
mm
ff
mmm
fff
mm
ff
m
f
VE
VE
AE
AE
AE
AE
A
A
P
P====
Isostress Condition
• Stress on the composite structure produces an equal stress condition on all the layers.
c = f = m
Assuming no change in area
and assuming unit length of the composite
c = fVf + mVm
Therefore
m
m
f
f
c
cEEE
=== ,,
Ec
=Vf
E f
+Vm
Em
1
Ec
=Vf
E f
+Vm
Em
Toughening Mechanisms in Composite Materials
• Toughening is due to fibers interfering with crack
propagation.
Crack deflection: Up on encountering reinforcement,
crack is deflected making propagation more
meandering.
Crack bridging: Fibers bridge the crack and help to
keep the cracks together.
Fiber pullout: Friction caused by pulling out the fiber
from matrix results in higher toughness.