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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. 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






2. Cracks pass through grains - often along specific crystal planes.






3. The Magnetization of the material - and is essentially the dipole moment per unit volume. It is proportional to the applied field. Xm is the magnetic susceptibility.






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






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






6. 1. Necking 2. Cavity formation 3. Cavity coalescence to form cracks 4. Crack propagation (growth) 5. Fracture






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






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






9. 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)






10. 1. Imperfections increase resistivity - grain boundaries - dislocations - impurity atoms - vacancies 2. Resistivity - increases with temperature - wt% impurity - and %CW






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






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






13. Stress concentration at a crack tips






14. Emitted light is in phase






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






16. Hardness is the resistance of a material to deformation by indentation - Useful in quality control - Hardness can provide a qualitative assessment of strength - Hardness cannot be used to quantitatively infer strength or ductility.






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






18. Cracks propagate along grain boundaries.






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






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






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






22. (sigma)=F/Ai (rho)=(rho)'(1+(epsilon))






23. - 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






24. Digitalized data in the form of electrical signals are transferred to and recorded digitally on a magnetic medium (tape or disk) - This transference is accomplished by a recording system that consists of a read/write head - "write" or record data by






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






26. Dimples on fracture surface correspond to microcavities that initiate crack formation.






27. 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






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






29. Different orientation of cleavage planes in grains.






30. 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






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






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






33. Small Coercivities - Used for electric motors - Example: commercial iron 99.95 Fe






34. 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






35. 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.






36. 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)






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






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

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






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






41. Sigma=ln(li/lo)






42. - 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






43. 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.






44. 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.






45. A high index of refraction (n value) allows for multiple internal reactions.






46. Is analogous to toughness.






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






48. 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."






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






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