Term
| y is thermal shock more of a problem for ceramics than metals? |
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Definition
| Ceramics have lower thermal conductivites that metals, so rapid increases/derceases of temperature will cause the surface to expand/contrct faster than the bulk, causing the surface to crack |
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Term
| Define a thermoplastic and a thermoset. |
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Definition
| Thermoplastic is composed of a long chain of molescules with a covalently bonded backbone and weak (van der waals or secondary) interactions between side groups. Thermosets are 3D networks of covalently bonded atoms |
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Term
| methods for creep mitigation |
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Definition
| 1) Single crystal 2) high temperature super alloys 3) high melting temperature material 4) Use ceramics 5) directional solidification |
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Term
| 4 methods for strengthening metals |
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Definition
| 1) coldwork: increases concentration of dislocations to block movement of dislocations. 2) Precipitation strengthening: generating more ceramic like properties 3) Solid solution: generate more internal mechanical strength which can block dislocations. 4) Increase Grain Boundaries to block dislocations |
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Term
| Explain the advantages and disadvantages of a ceramic matrix; metal matrix; polymer matrix. |
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Definition
| Cermaics: high strength, low ductility. Polymers/Metals: High ductility, low strength |
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Term
| Explain why metals are good electrical conductors, in terms of their energy bands. |
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Definition
| There is an overlapping of their conductive and valance bands |
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Term
| When a metal's temperatuer is raised, what effect will that have on its thermal conductivity |
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Definition
| Increasing the temperature causes more atomic vibrations which scatters electrons and therefore lowers thermal conductivity. Coldworking likewise causes dislocations which scatters electrons and raises resistivity |
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Term
| Methods of improving fatigue lifetime of materials |
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Definition
| Impose a compressive surface stress (carbonizing or shot peening) or removing stress concentrators |
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Term
| methods of toughening cermics |
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Definition
| 1) Fiber reinforcements (pulling fibers through matrix 2) polish/buffer or better process control to reduce the size of serface cracks 3) metal particles can blunt or block cracks 4) matrix microcracking (presence of many small cracks can blunt large ones) 5) phase transformation toughening--when a crack nears a particle, the particle changes to a new phase with a higher volume which compresses the crack |
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| length of a side for diamond of silicon |
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Definition
| volume of atoms in unit cell/total unt cell volume |
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Definition
| #atoms in structure*4/3*pi*R^3/volume |
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| # atoms in diamond/silicon |
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Definition
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Term
| What is the charge of a Cl vacancy in NaCl? |
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Definition
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Term
| Why are ceramics brittle? |
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Definition
| Has covlanent (directional) bonds, which decreaseing the mobility of dislocations |
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Term
| How do you calculate and what is the phyiscal meaning of Young's Modulus |
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Definition
| Stiffness. Slope of the linear portion of the stress-strain curve, E=(Change in lenght)/length= stress/strain |
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Term
| How do you calculate and what is the phyiscal meaning of Ultimate Tensile Stress |
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Definition
| largest stress required to deform metal. Miximum of stress strain curve |
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Term
| How do you calculate and what is the phyiscal meaning of Fracture stress |
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Definition
| Strass at fracture. Last point on stress strain curve |
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Term
| How do you calculate and what is the phyiscal meaning of yield strength |
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Definition
| stress which results in permanent strain of .2%, point when the graph is no longer linear |
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Term
| How do you calculate and what is the phyiscal meaning of ductility |
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Definition
| %EL=(Lf-Lo)/Lo*100, if the part of the curve extends for a longer period after linearity ends |
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Term
| How do you calculate and what is the phyiscal meaning of toughness |
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Definition
| Ability to absorb mechanical energy due to plastic deformation. Area under the stress strain curve |
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| calculate the carrier concentration when given the density of the semiconductor and atomic percent of dopants |
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Definition
| N=1/(charge*dopant concentration per cm^3*carrier mobility) |
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Term
| Explain why certain organic semiconductor materials can be used for flexiable or transparaent displays |
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Definition
| multilayered OLEDS improve device efficency, intermolecular interactions are much weaker, bond gaps are larger |
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Term
| What is the physical meaninf of an energy band? |
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Definition
| also called a band gap. An energy range where no electron states can exist |
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Term
| Compare organic and inorganic semiconductors in terms of their mechanical properties and carier transporting methods |
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Definition
| Inorganic: electrons move in conduction band and holes move in valance band. Organic: intermolecular interactions are much weaker (van der waals and london forces), electrons move in lowest occupied molecular orbital (LUMO), holes in highest occupied molecular orbital (HOMO) |
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Explain how a typical expoxy is cross-linked |
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Definition
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Term
What's the Mech form
forming branched polymers
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| How to dislocation move & what effect does their movement have |
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| Explain how a Pn-Junction functions under forward and Reverse bias Conditions |
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| Determine if a part will fracture given K1C |
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| Given an S-N Curve determine if a part can survive a given # of cycles at a given stress |
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| Calculate the mass-Average and # avg molecular weight of a sample |
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Definition
1) Primary: material work hardens, creates dislocations
2) Secondary: Steady state, as temperature increases, grain boundaries decreases as dislocations increase
3) Tertiarry: rapid elongation due to necking and/or void growth. Dislocations move to grain boundaries |
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Definition
left to right: decreases
top to bottom: increases |
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Top to Bottom: decreases
Left to Right: Increases |
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| Draw an energy band diagram for an N-type semiconductor |
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Definition
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Term
| If a .2wt% C alloy wasrapidly quenched from 1100 to 100C what structure would form |
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Definition
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Term
| How do the mechanical properties of .3% C steel compare with those of a .5% C steel at RT |
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Definition
| lower strength and higher ductility |
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Term
Length of unit cell for
BCC
FCC
HCP |
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| please choose the correct drawing for disproportion step in the synthesis of polyethylene |
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| 14) choose draining for thermoplastic polymer |
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Definition
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| 15) drawing for thermoset polymers |
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Definition
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Term
| Draw an energy band diagram for ptype |
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