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38 Cards in this Set
- Front
- Back
For glassy materials, cooling is accompanied by:
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continuous specific volume decrease
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Viscosity is a measure of a glassy material's resistance to
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deform under shear stress
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Crystal structure of a perovskite material is
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ABX3
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Isomerism is best described as
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having the same chemical equation but different structure
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Glass-forming operations are performed at a temperature range
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between the softening point and working point
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Stress relaxation of the polymer is a result of
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thermally activated sliding of polymer molecules
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In crystalline ceramics, coordination number depends upon
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cation-anion radius ration
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The possible crystal structure of a ceramic containing Mg and O will be that of
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NaCl
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Flexural strength of a ceramic material is generally
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greater than the tensile fracture strength
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Larger volume fraction of the stiff and brittle fibers makes the composite
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more stiff and less ductile
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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
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0.44
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An example of a particle reinforced composite is
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concrete and spheroidite
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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
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same strain
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Modulus of a fiber-reinforced composite with continuous aligned fibers is at its maximum in the direction
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parallel to the fibers
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The load taken up by the fiber in a fiber-reinforced composite when loaded along the direction of the fibers is proportional to
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product of modulus and volume fraction of the fibers
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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
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same stress
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Crack bridging by fibers refers to
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fibers not allowing the crack surfaces to open up
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A small molecular weight byproduct usually forms in the following reaction
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condensation polymerization
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A Schottky defect is
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a cation vacancy and an anion vacancy
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The elastic behavior of the elastomers arises from
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stretching and aligning of the polymer chains
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The tendency to form a crystalline polymer increases with
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linear or one-dimensional polymerization
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The rigidity or the modulus of the polymer increases with
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cross-linking or branching
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As a polymer becomes more branched, the tendency to crystallize
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decreases
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Cross-linking in polymers
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increases the modulus
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A polymer fiber is stronger than the bulk polymer because
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the molecules are oriented along the fiber axis and strong covalent bonds support the load
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Larger amounts of initiator and terminator compound cause the degree of polymerization to
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decrease
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During addition polymerization, monomers are linked together by
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replacing a double bond with two single bonds
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The cross-linking in vulcanization of rubber (polyisoprene) is achieved through
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sulfur atoms
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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.
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0.78 psi
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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
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1.95 psi
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A Frenkel defect is
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when a cation is out of place
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As %Crystallinity increases
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TS and modulus INCREASE
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Annealing causes
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crystalline regions to grow, %crystallinity increase
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Thermoplastics
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have little cross-linking, are ductile, soften with heating
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With decreasing temp or increasing strain rate in thermoplastics
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modulus increases, TS increases, %EL decreases
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MMC (metals) are dispersed in composite materials to
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increase yield stress, TS, and creep resistance
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CMC (ceramics) are dispersed in composite materials to
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increase Kc (crack bridging), toughness
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PMC (polymers) are dispersed in composite materials to
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increase modulus, yield stress, TS, and creep resistance
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