# ChE 361 #2

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1. Which material criterion should used to minimize the mass for a given beam stiffness?
Maximize E/p
2. Suppose the price per kilogram of material is denoted by Cm. Which criterion should be used to minimize the price for a given beam stiffness?
Maximize E/Cmp
3. Equation for stiffness
F/(displacement)
Compression
5. Which factor from equation Fcrit=(n2pi2EI)/L2 depends on the shape of a structural member and the square of its cross-sectional area?
I
6. Which kinds of structural members are most susceptible to buckling?
long columns
7. If the geometry of the beam or plate is held constant, how does the vibrational frequency scale with material properties?
f=(E/p)1/2
8. A hard diamond indenter is pressed into the surface of a material with force F, creating a permanent indentation of depth l and area A. Suppose the material has modulus E, shear modulus G, and strength sigma. How is the hardness computed from this test?
F/A
9. According to the text, what is the approximate relationship between hardness and yield strength for many materials?
H=3(yield strength)
10. The tensile strain at fracture is a measure of which property?
Ductility
11. Where does the largest shear stress occur in s sample subjected to a tensile load?
Planes inclined at 45 to the tensile load
12. What drives dislocation glide?
Shear stress
13. What are four ways to strengthen a metal?
• 1. dispersion of small particles
• 2. introduction of solutes
• 3. reduction of grain size
• 4. plastic deformation
14. What are four ways to strengthen a polymer?
• reinforcement of fibers like glass
• blending with stronger polymer
• drawing
15. How is work-hardening explained?
Dislocations obstruct each other
16. What is intrinsic strength?
Strong atomic bonds resist dislocation movement
17. How is solid solution hardening explained?
Solute-generated stresses "roughen" slip planes
18. How is dispersion strengthening explained?
Precipitates obstruct dislocation movement
19. What occurs during elastic deformation?
Atomic bonds stretch but do not break
20. What is annealing?
Heating removes dislocations
21. What is cold working of a metal?
Plastic deformation without heating
22. How can work-hardening be reversed?
Annealing
23. What causes many materials to yield at stresses far below their ideal strength?
dislocations
24. What is an edge dislocation?
An extra half plane of atoms
25. What is a glide plane?
Plane which a dislocation moves
26. Identify each of the quantities in following equation:
Y(sigma)(pi*c)1/2=(EGc)1/2
• Y=correction factor
• sigma=nominal stress
• c=crack length
• Gc=toughness
• E=elastic modulus
• (EGc)1/2=fracture toughness
27. Which phenomenon does Y(sigma)(pi*c)1/2=(EGc)1/2 describe?
Fast fracture
28. What causes brittle fracture?
long, sharp-tipped cracks
29. What can happen at the tip of a crack when local stress exceeds the ideal strength?
Crack propagates by cleavage
30. What can happen at the tip of a crack when local stress exceeds the yield strength?
Plastic deformation that blunts the crack tip
31. How does ductile fracture occur?
Linking of voids in plastic zone
32. How can the addition of glass fiers to a polymer matrix crate a tough composite?
Gibers act as crack stoppers
33. Why are many ductile materials also quite tough?
Energy is consumed by plastic flow
34. How do cracks start in an uncracked component subject to high-cycle fatigue?
Local plasticity occurs where scratches or section changes concentrate stess
35. How do cracks start in an uncracked component subject to low-cycle fatigue?
General plasticity roughens the surface
36. What happens during peening?
Residual surface compressive stresses are introduced
37. What causes work-hardening?
Dislocations accumulate and hinder each other
Fails by fast fracture
39. In the context of this course, what is fatigue?
Failure of a structure due to cyclic stress
40. Which process(es) can cause the formation and slow growth of cracks at loads well below the yield strength?
Corrosion
41. Which process generally causes final failure in fatigue?
Fast fracture
42. What is the cyclic stress intensity range, delta(K)?
Kmax-Kmin or Y(delta(sigma))(pi*c)1/2
43. What is the definition of the mean stress?
(sigmamax+sigmamin)/2
44. What is the definition of the stress amplitude?
(Sigmamax-sigmamin)/2
45. What is the definition of the cyclic stress range?
sigmamax-sigmamin
 Author: deshayes ID: 52724 Card Set: ChE 361 #2 Updated: 2010-12-03 05:42:52 Tags: Quizzes Folders: Description: Engineering materials final Show Answers: