Introduction to Materials Exam 2
Name _______________________________________
MIE Introduction to Materials, Fall ‘08
Exam #2
Answer all 5 Questions
(Please keep your writing neat, use full sentences, and make the writing large enough so that it can be read.)
Problem #1
a) Describe the difference between the substitutional and the interstitial mechanism for mass transport - diffusion in metals.
b) Do these two mechanisms control mass transport – diffusion in 1) ceramics and 2) polymers? Explain your answers.
c) Given the table of data below, which metal (iron - Fe, tungsten - W, or copper - Cu) has the highest self diffusion coefficient, D, at 950oC. Explain your reasoning.
Metal Melting Point (oC) Crystal Structure σy (MPa) KIC (MPam1/2)
Fe 1538 fcc 180 50
W 3410 bcc 522 80
Cu 1085 fcc 69 35
Problem #2
a) Draw a typical true stress - strain curve, σT vs εT, for a metal. Indicate the yield point, and the point where necking takes place.
b) Using this curve describe the process of strain hardening including the effect of dislocations. Describe the strain hardening relationship, σT = K(εT)n , where K and n are constants. Finally, give a practical process that will strain harden an alloy.
c) Thermal processing of a metal allows for the recovery of the initial mechanical properties of an alloy. Describe briefly the recrystallization process indicating the driving force for the process, the change in the defect structure of the alloy, and the change in microstructure, if any.
d) Describe a second process which can strengthen a metal. Also, explain the importance of dislocations to the process of strengthening in this example.
Problem #3
a) Polymer and ceramic deformation are not controlled by dislocations. Explain this statement.
b) Semi-crystalline polymers have stress – strain curves similar to those of metals (Problem #2, part a). Explain how elastic and plastic deformation takes place
MIE Introduction to Materials, Fall ‘08
Exam #2
Answer all 5 Questions
(Please keep your writing neat, use full sentences, and make the writing large enough so that it can be read.)
Problem #1
a) Describe the difference between the substitutional and the interstitial mechanism for mass transport - diffusion in metals.
b) Do these two mechanisms control mass transport – diffusion in 1) ceramics and 2) polymers? Explain your answers.
c) Given the table of data below, which metal (iron - Fe, tungsten - W, or copper - Cu) has the highest self diffusion coefficient, D, at 950oC. Explain your reasoning.
Metal Melting Point (oC) Crystal Structure σy (MPa) KIC (MPam1/2)
Fe 1538 fcc 180 50
W 3410 bcc 522 80
Cu 1085 fcc 69 35
Problem #2
a) Draw a typical true stress - strain curve, σT vs εT, for a metal. Indicate the yield point, and the point where necking takes place.
b) Using this curve describe the process of strain hardening including the effect of dislocations. Describe the strain hardening relationship, σT = K(εT)n , where K and n are constants. Finally, give a practical process that will strain harden an alloy.
c) Thermal processing of a metal allows for the recovery of the initial mechanical properties of an alloy. Describe briefly the recrystallization process indicating the driving force for the process, the change in the defect structure of the alloy, and the change in microstructure, if any.
d) Describe a second process which can strengthen a metal. Also, explain the importance of dislocations to the process of strengthening in this example.
Problem #3
a) Polymer and ceramic deformation are not controlled by dislocations. Explain this statement.
b) Semi-crystalline polymers have stress – strain curves similar to those of metals (Problem #2, part a). Explain how elastic and plastic deformation takes place