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38 Cards in this Set

  • Front
  • Back
For glassy materials, cooling is accompanied by:
continuous specific volume decrease
Viscosity is a measure of a glassy material's resistance to
deform under shear stress
Crystal structure of a perovskite material is
ABX3
Isomerism is best described as
having the same chemical equation but different structure
Glass-forming operations are performed at a temperature range
between the softening point and working point
Stress relaxation of the polymer is a result of
thermally activated sliding of polymer molecules
In crystalline ceramics, coordination number depends upon
cation-anion radius ration
The possible crystal structure of a ceramic containing Mg and O will be that of
NaCl
Flexural strength of a ceramic material is generally
greater than the tensile fracture strength
Larger volume fraction of the stiff and brittle fibers makes the composite
more stiff and less ductile
A composite is made of copper matrix with aligned tungsten fibers. The volume fraction of tungsten fibers (Ew=1 GPa) required to increase the modulus of the copper matrix (Ecu=0.1 GPa) in the fiber direction to 0.5 GPa is
0.44
An example of a particle reinforced composite is
concrete and spheroidite
When the load is applied to a continuous aligned fiber-reinforced composite in the direction of the fiber alignment, the fiber and the matrix are subject to
same strain
Modulus of a fiber-reinforced composite with continuous aligned fibers is at its maximum in the direction
parallel to the fibers
The load taken up by the fiber in a fiber-reinforced composite when loaded along the direction of the fibers is proportional to
product of modulus and volume fraction of the fibers
When the load is applied to a fiber-reinforced composite in the transverse direction (normal to the direction of the fiber alignment) the fiber and matrix are subjected to
same stress
Crack bridging by fibers refers to
fibers not allowing the crack surfaces to open up
A small molecular weight byproduct usually forms in the following reaction
condensation polymerization
A Schottky defect is
a cation vacancy and an anion vacancy
The elastic behavior of the elastomers arises from
stretching and aligning of the polymer chains
The tendency to form a crystalline polymer increases with
linear or one-dimensional polymerization
The rigidity or the modulus of the polymer increases with
cross-linking or branching
As a polymer becomes more branched, the tendency to crystallize
decreases
Cross-linking in polymers
increases the modulus
A polymer fiber is stronger than the bulk polymer because
the molecules are oriented along the fiber axis and strong covalent bonds support the load
Larger amounts of initiator and terminator compound cause the degree of polymerization to
decrease
During addition polymerization, monomers are linked together by
replacing a double bond with two single bonds
The cross-linking in vulcanization of rubber (polyisoprene) is achieved through
sulfur atoms
A polyethylene sample is subjected at room temp (27 C) to a tensile stress of 50 psi. The stress relaxes to 25 psi after 5 minutes with the cross-heads held without movement. Calculate the stress 30 min after the sample was pulled in tension.
0.78 psi
Temp 27C, initial stress of 50 psi, relaxes to 25 psi after 5 min. Calculate relaxation modulus Er 30 min after the sample was pulled in tension if a measured strain is 0.4
1.95 psi
A Frenkel defect is
when a cation is out of place
As %Crystallinity increases
TS and modulus INCREASE
Annealing causes
crystalline regions to grow, %crystallinity increase
Thermoplastics
have little cross-linking, are ductile, soften with heating
With decreasing temp or increasing strain rate in thermoplastics
modulus increases, TS increases, %EL decreases
MMC (metals) are dispersed in composite materials to
increase yield stress, TS, and creep resistance
CMC (ceramics) are dispersed in composite materials to
increase Kc (crack bridging), toughness
PMC (polymers) are dispersed in composite materials to
increase modulus, yield stress, TS, and creep resistance