...

幻灯片 1

by user

on
51

views

Report

Comments

Transcript

幻灯片 1
1. Indicate whether statements are
true or false
①
②
③
④
Most processing routes for ceramic matrix composites
involve high temperature and can only be employed
with reinforcement capable of withstanding such as
temperature.
Chemical vapour infiltration is simply chemical vapor
deposition applied to the formation of a matrix in a
porous preform.
Stabilizing oxide, such as Y2O3, are added to the
Zirconia in zirconia toughened alumina in order to
enhance the transformation to the monoclinic state.
The carbon yield from pitch is greatly improved on
increasing the pressure
⑤ Crack deflection can be caused by the
interaction of the crack with the residual
stress fields due to differences in the
thermal expansion coefficients or in
elastic moduli between the matrix and
the reinforcement.
⑥ The energy of pull-out is much less than
the energy required for debonding
2. For each of the statements of following
questions, one or more of the completions given
are correct. Choose the correct completions.
①
A slurry is
a)
b)
c)
d)
e)
②
A sol,
A sol that has lost some liquid,
A dispersion in a liquid of small particles of less than 100 nm,
A suspension of large (typical 1-50mm) particles in liquid,
A gel.
Pruduction of a CMC by impregnation of a preform with a
ceramic-producing polymer
a)
b)
c)
d)
e)
Requires a heat treatment which may be at relatively low
temperature in the range 600 – 1000℃,
Involves pyrolysis (高温分解) of the polymer,
Is extremely rapid as the ceramic yield is high,
Requires multiple impregnations as the ceramic yield is low,
Is used to produce some carbon-carbon composites.
③
Reinforcing alumina with SiC whiskers
a)
b)
c)
d)
e)
Enhances the thermal shock resistance,
Lowers the coefficient of thermal expansion,
Decrease the thermal conductivity,
Increase density,
Improves the toughness.
④ Chemical vapor deposition of a carbon matrix
a)
b)
c)
d)
e)
Is also commonly known as gas carbonization,
is also commonly known as chemical vapor infiltration,
Produces a brittle composite with a glassy matrix,
Is independent of deposition pressure,
Is dependent on deposition temperature,
5. Oxidation protection of carbon-carbon composites
a)
b)
c)
d)
6.
Toughening by crack bowing
6.
7.
8.
9.
10.
7.
Currently is only satisfactory up to temperature of 1400℃,
Normally involves an alumina or zirconia coat,
Normally involves a silicon nitride or carbide coat,
May consist of a primary oxidation barrier coat and secondary
protection.
Results in a non-planar crack,
Results in a nonlinear crack front,
Is greater the smaller the aspect ratio of the reinforcement,
Is greater the larger the volume fraction of reinforcement,
Is independent of the mechanical properties of the reinforcement.
Fibre bridging toughening
a)
b)
c)
d)
If associated with particulate reinforcement is known as crack
deflection,
Occurs mainly at the crack tip,
Leads to an increasing resistance to crack growth at the crack growth,
Leads to what is known as R-curve behaviors.
Fly UP