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Engineering Materials

Subject : engineering
Instructions:
  • Answer 50 questions in 15 minutes.
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  • Match each statement with the correct term.
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This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.
1. Light Amplification by Stimulated Emission of Radiation






2. As the applied field (H) increases the magnetic domains change shape and size by movement of domain boundaries.






3. 1. Stress-strain behavior is not usually determined via tensile tests 2. Material fails before it yields 3. Bend/flexure tests are often used instead.






4. 1. Diamagnetic (Xm ~ 10^-5) - small and negative magnetic susceptibilities 2. Paramagnetic (Xm ~ 10^-4) - small and positive magnetic susceptibilities 3. Ferromagnetic - large magnetic susceptibilities 4. Ferrimagnetic (Xm as large as 10^6) - large m






5. There is always some statistical distribution of flaws or defects.






6. Measures Hardness - No major sample damage - Each scales runs to 130 but only useful in range 20-100 - Minor load is 10 kg - Major load: 60 kg (diamond) - 100 kg (1/16 in. ball) - 150 kg (diamond)






7. Large coercivities - Used for permanent magnets - Add particles/voids to inhibit domain wall motion - Example: tungsten steel






8. Dramatic change in impact energy is associated with a change in fracture mode from brittle to ductile.






9. Allows flow of electrons in one direction only (useful to convert alternating current to direct current) - Result: no net current flow






10. Is reflected - absorbed - scattered - and/or transmitted: Io=It+Ia+Ir+Is






11. Allows you to calculate what happened G=F' x cos(lambda) - F=F' x cos(phi)






12. 1. Hard disk drives (granular/perpendicular media) 2. Recording tape (particulate media)






13. To build a device - various thin metal or insulating films are grown on top of each other - Evaporation - MBE - Sputtering - CVD (ALD)






14. 1. Tensile (opening) 2. Sliding 3. Tearing






15. Elastic means reversible! This is not a permanent deformation.






16. Growth of an oxide layer by the reaction of oxygen with the substrate - Provides dopant masking and device isolation - IC technology uses 1. Thermal grown oxidation (dry) 2. Wet Oxidation 3. Selective Oxidation






17. Plastic means permanent! When a small load is applied - bonds stretch & planes shear. Then when the load is no longer applied - the planes are still sheared.






18. Emitted light is in phase






19. - The emission of light from a substance due to the absorption of energy. (Could be radiation - mechanical - or chemical energy. Could also be energetic particles.) - Traps and activator levels are produced by impurity additions to the material - Whe






20. 1. Ductility- % elongation - % reduction in area - may be of use in metal forming operations (e.g. - stretch forming). This is convenient for mechanical testing - but not very meaningful for most deformation processing. 2. Toughness- Area beneath str






21. 1. Insulators: Higher energy states NOT ACCESSIBLE due to gap 2. Semiconductors: Higher energy states separated by a smaller gap.






22. 1. General yielding occurs if flaw size a < a(critical) 2. Catastrophic fast fracture occurs if flaw size a > a(critical)






23. Specific heat = energy input/(mass*temperature change)






24. Is analogous to toughness.






25. Loss of image transmission - You get no image - There is no light transmission - and therefore reflects - scatters - or absorbs ALL of it. Both mirrors and carbon black are opaque.






26. For a metal - there is no ______ - only reflection






27. Materials change size when temperature is changed






28. The ability of a material to be rapidly cooled and not fracture






29. A parallel-plate capacitor involves an insulator - or dielectric - between two metal electrodes. The charge density buildup at the capacitor surface is related to the dielectric constant of the material.






30. Second phase particles with n > glass.






31. Increase temperature - increase in interatomic separation - thermal expansion






32. (sigma)=K(sigma)^n . K = strength coefficient - n = work hardening rate or strain hardening exponent. Large n value increases strength and hardness.






33. Degree of opacity depends on size and number of particles - Opacity of metals is the result of conduction electrons absorbing photons in the visible range.






34. Occur when lots of dislocations move.






35. Specular: light reflecting off a mirror (average) - Diffuse: light reflecting off a white wall (local)






36. Not ALL the light is refracted - SOME is reflected. Materials with a high index of refraction also have high reflectance - High R is bad for lens applications - since this leads to undesirable light losses or interference.






37. Measures Hardness 1. psia = 500 x HB 2. MPa = 3.45 x HB






38. Sigma=ln(li/lo)






39. Flaws and Defects - They concentrate stress locally to levels high enough to rupture bonds.






40. 1. Fluorescent Lamp - tungstate or silicate coating on inside of tube emits white light due to UV light generated inside the tube. 2. TV screen - emits light as electron beam is scanned back and forth.






41. Defines the ability of a material to resist fracture even when a flaw exists - Directly depends on size of flaw and material properties - K(ic) is a materials constant






42. Failure under cyclic stress 1. It can cause part failure - even though (sigma)max < (sigma)c 2. Causes ~90% of mechanical engineering failures.






43. Occur due to: restrained thermal expansion/contraction -temperature gradients that lead to differential dimensional changes sigma = Thermal Stress






44. Different orientation of cleavage planes in grains.






45. - A magnetic field is induced in the material B= Magnetic Induction (tesla) inside the material mu= permeability of a solid






46. With Increasing temperature - the saturation magnetization diminishes gradually and then abruptly drops to zero at Curie Temperature - Tc.






47. These are liquid crystal polymers- not your normal "crystal" -Rigid - rod shaped molecules are aligned even in liquid form.

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48. Created by current through a coil N= total number of turns L= length of turns (m) I= current (ampere) H= applied magnetic field (ampere-turns/m) Bo= magnetic flux density in a vacuum (tesla)






49. Found in 26 metals and hundreds of alloys & compounds - Tc= critical temperature = termperature below which material is superconductive.






50. Growing interconnections to connect devices -Low electrical resistance - good adhesion to dielectric insulators.







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