MSE201 Midterm Exam 10/17/2014 Each element 2 points. Put ALL calculations and answers in your Blue Book! 1. Materials are characterized by: a. Macroscopic properties b. Microstructure c. Atomic level composition d. All of the above 2. Atoms are: a. Discrete units of matter b. An abstract concept c. Found in fractional units d. Crystallographic lattice points 3. The Burger’s vector describes: a. Surface cracks b. Crystal twinning c. Dislocation geometry d. The most direct route to McDonald’s 4. Cubic Close Packed (CCP) is another name for which of the following: a. HCP b. BCC c. FCC d. All of the above 5. Glass and ceramic materials tend to: a. Fail catastrophically at low strain b. Show ductility c. Deform plastically before failure d. Have elastic moduli ~106 Pa 6. Solid state diffusion & vacancy generation: a. Are completely unrelated b. Are directly related c. Increase linearly with Temperature d. Describe lattice point motion 7. Diffusion & heat transfer: a. Are completely unrelated b. Are directly related c. Increase linearly with Temperature d. Have identical differential equations 8. A vacancy and a dislocation both: a. Disrupt the crystal lattice b. Represent partial occupancy c. Contain ruptured bonds d. Are low energy regions 9. Dislocations: a. Are interstitial dopants b. Are crystal defects c. Require atomic impurities d. Enhance plastic deformation 10. Ionic, covalent and metallic bonding are primary bonding types. a. Primary bonds require exchange or sharing of what between atoms? b. How does electronegativity drive the reaction of sodium metal and chlorine gas to form sodium chloride? c. Carbon-carbon bonds are what type? d. The directional nature of covalent bonds is related to what structural feature of atoms? 11. The (111) plane of the FCC structure is close-packed. a. Sketch this plane within a unit cell. b. How many atoms are on the plane you drew inside the unit cell? c. Estimate the area of the plane d. Calculate the area atomic density e. If there is one vacancy per 1012 lattice points at 273K, what is the partial atomic occupancy of each lattice point? f. If you are asked calculate the number of vacancies present at 600K, what additional information do you need? 12. Dislocation motion occurs largely along close-packed directions and planes. First, compare the FCC & BCC structures: a. Describe any close packed planes b. Describe any close packed directions c. If the ductile-to-brittle transition at low temperatures is related to the number of close-packed directions and planes, do you expect BCC or FCC metals to have greater ductility? d. Magnesium and other HCP metals are brittle. Does your analysis from 12.c. support this observation? 13. A tensile test is performed on a ductile sample. The first 1% of strain is elastic with a modulus of 100E9 Pa, at which point plastic deformation begins. The tensile strength of 1.1E9 Pa is determined at 9% strain, while failure occurs at a stress of 9E8 Pa and strain of 18%. a. Sketch the complete stress-strain cycle b. Estimate the toughness in units of J/m3.
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