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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.
  • Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

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. Increase temperature - no increase in interatomic separation - no thermal expansion






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






3. 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






4. 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.






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






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






7. No appreciable plastic deformation. The crack propagates very fast; nearly perpendicular to applied stress. Cracks often propagate along specific crystal planes or boundaries.






8. 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.






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






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






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






12. 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.






13. Is analogous to toughness.






14. Cracks propagate along grain boundaries.






15. 1. Data for Pure Silicon - electrical conductivity increases with T - opposite to metals






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






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






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






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






20. Different orientation of cleavage planes in grains.






21. 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.






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






23. 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






24. A measure of the ease with which a B field can be induced inside a material.






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






26. Width of smallest feature obtainable on Si surface






27. 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






28. Stress concentration at a crack tips






29. 1. Ability of the material to absorb energy prior to fracture 2. Short term dynamic stressing - Car collisions - Bullets - Athletic equipment 3. This is different than toughness; energy necessary to push a crack (flaw) through a material 4. Useful in






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






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






32. High toughness; material resists crack propagation.






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






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






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






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






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






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






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






40. Typical loading conditions are _____ enough to break all inter-atomic bonds






41. 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.






42. 1. Electron motions 2. The spins on electrons - Net atomic magnetic moment: sum of moments from all electrons.






43. 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






44. Second phase particles with n > glass.






45. Sigma=ln(li/lo)






46. Process by which metal atoms diffuse because of a potential.






47. 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.






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






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

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50. 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