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Engineering Materials

Subject : engineering
Instructions:
  • Answer 50 questions in 15 minutes.
  • If you are not ready to take this test, you can study here.
  • 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. Superconductors expel magnetic fields - This is why a superconductor will float above a magnet.






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






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






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






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






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






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






8. 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.






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






11. 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






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






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






14. Different orientation of cleavage planes in grains.






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






16. Light Amplification by Stimulated Emission of Radiation






17. 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."






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






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






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






21. 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






22. High toughness; material resists crack propagation.






23. 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.






24. 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.






25. 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






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






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






28. These materials are relatively unaffected by magnetic fields.






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






30. Emitted light is in phase






31. Cracks propagate along grain boundaries.






32. 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






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






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






35. 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.






36. Is analogous to toughness.






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






38. 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






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






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






41. They are used to assess properties of ceramics & glasses.






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. Width of smallest feature obtainable on Si surface






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


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






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






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






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






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






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