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






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

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






4. 1. Tc= critical temperature- if T>Tc not superconducting 2. Jc= critical current density - if J>Jc not superconducting 3. Hc= critical magnetic field - if H > Hc not superconducting






5. The ability of a material to transport heat - Atomic Perspective: Atomic vibrations and free electrons in hotter regions transport energy to cooler regions - Metals have the largest values






6. Reflectiviy is between 0.90 and 0.95 - Metal surfaces appear shiny - Most of absorbed light is reflected at the same wavelength (NO REFRACTION) - Small fraction of light may be absorbed - Color of reflected light depends on wavelength distribution of






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






8. The magnetic hysteresis phenomenon: Stage 1: Initial (unmagnetized state) Stage 2: Apply H - align domains Stage 3: Remove H - alignment remains => Permanent magnet Stage 4: Coercivity - Hc negative H needed to demagnitize Stage 5: Apply -H - align d






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






10. Wet: isotropic - under cut Dry: ansiotropic - directional






11. Metals are good conductors since their _______is only partially filled.






12. Transformer cores require soft magnetic materials - which are easily magnetized and de-magnetized - and have high electrical resistivity - Energy losses in transformers could be minimized if their cores were fabricated such that the easy magnetizatio






13. Sigma=ln(li/lo)






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






15. Ability to transmit a clear image - The image is clear.






16. 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






17. Occurs at a single pore or other solid by refraction n = 1 for pore (air) n > 1 for the solid - n ~ 1.5 for glass - Scattering effect is maximized by pore/particle size within 400-700 nm range - Reason for Opacity in ceramics - glasses and polymers.






18. Without passing a current a continually varying magnetic field will cause a current to flow






19. Resistance to plastic deformation of cracking in compression - and better wear properties.






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






21. Becomes harder (more strain) to stretch (elongate)






22. ...occurs in bcc metals but not in fcc metals.






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






24. Rho=F/A - tau=G/A . Depending on what angle the force is applied - and what angle the crystal is at - it takes different amounts of force to induce plastic deformation.






25. These materials are "attracted" to magnetic fields.






26. 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






27. 1. Yield = ratio of functional chips to total # of chips - Most yield loss during wafer processing - b/c of complex 2. Reliability - No device has infinite lifetime. Statistical methods to predict expected lifetime - Failure mechanisms: Diffusion reg






28. Energy is stored as atomic vibrations - As temperature increases - the average energy of atomic vibrations increases.






29. - Metals that exhibit high ductility - exhibit high toughness. Ceramics are very strong - but have low ductility and low toughness - Polymers are very ductile but are not generally very strong in shear (compared to metals and ceramics). They have low






30. heat flux = -(thermal conductivity)(temperature gradient) - Defines heat transfer by CONDUCTION

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






32. This strength parameter is similar in magnitude to a tensile strength. Fracture occurs along the outermost sample edge - which is under a tensile load.






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






34. 1. Metals: Thermal energy puts many electrons into a higher energy state. 2. Energy States: Nearby energy states are accessible by thermal fluctuations.






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






36. Another optical property - Depends on the wavelength of the visible spectrum.






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






38. Liquid polymer at room T - sandwiched between two sheets of glass - coated with transparent - electrically conductive film. - Character forming letters/ numbers etched on the face - Voltage applied disrupts the orientation of the rod- shaped molecule






39. The size of the material changes with a change in temperature - polymers have the largest values






40. Measures impact energy 1. Strike a notched sample with an anvil 2. Measure how far the anvil travels following impact 3. Distance traveled is related to energy required to break the sample 4. Very high rate of loading. Makes materials more "brittle."






41. # of thermally generated electrons = # of holes (broken bonds)






42. A three terminal device that acts like a simple "on-off" switch. (the basis of Integrated Circuits (IC) technology - used in computers - cell phones - automotive control - etc) - If voltage (potential) applied to the "gate" - current flows between th






43. Transmitted light distorts electron clouds - The velocity of light in a material is lower than in a vacuum - Adding large ions to glass decreases the speed of light in the glass - Light can be "bent" (or refracted) as it passes through a transparent






44. Impurities added to the semiconductor that contribute to excess electrons or holes. Doping = intentional impurities.






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






46. Cp: Heat capacity at constant pressure Cv: Heat capacity at constant volume.






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






48. Because of ionic & covalent-type bonding.






49. Materials change size when temperature is changed






50. 1. Impose a compressive surface stress (to suppress surface cracks from growing) - Method 1: shot peening - Method 2: carburizing 2.Remove stress concentrators.







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