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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. Stress concentration at a crack tips






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






3. Materials change size when temperature is changed






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






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






6. 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






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






8. 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






9. -> fluorescent light - electron transitions occur randomly - light waves are out of phase with each other.






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






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






12. Cracks propagate along grain boundaries.






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






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


15. Emitted light is in phase






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






17. Undergo little or no plastic deformation.






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






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






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






21. 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






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






23. 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.






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






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






26. Diffuse image






27. 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.






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






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






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






32. Ohms Law: voltage drop = current * resistance






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






34. 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






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






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






37. Sigma=ln(li/lo)






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






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






40. Because of ionic & covalent-type bonding.






41. Is analogous to toughness.






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


43. 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






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






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






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






47. High toughness; material resists crack propagation.






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






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






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