HW4 - surface of the plate is exposed). How long will it...

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Louisiana State University Mechanical Engineering Department Professor Meletis ME 2733 Fall 2004 Materials of Engineering Homework Assignment #4 (due: in class Wednesday, October 13, 2004) 1. The free energy of vacancy formation for Ni is 1.2 eV. (a) Calculate the equilibrium concentration of vacancies at 400 o C. (b) What is the maximum concentration of vacancies that can exist in solid Ni? 2. The diffusivity of Cu in a commercial brass alloy is 10 -20 m 2 /s at 400 o C. The activation energy for diffusion of Cu in this system is 195 kJ/mol. Calculate the diffusivity at 500 o C. 3. A thick low carbon steel plate (initial composition 0.1 wt% C) is heated to 1000 ° C in a carbonaceous atmosphere (CH 4 ) to be carburized (hardened by diffusing C). The carburization conditions keep the carbon surface concentration constant at 0.8% C (assume that only one
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Unformatted text preview: surface of the plate is exposed). How long will it take to achieve a carbon concentration of 0.4 wt% at a 2 mm depth from the surface? [Fe at 1000 o C is FCC and is called -Fe.] 4. The following load versus extension curves were obtained from tensile tests of two wires A and B, both 10 inches long and 0.1 in 2 in cross sectional area. For Material A calculate: (a) the elastic modulus; (b) the yield strength and ultimate tensile strength; (c) the strain-at-fracture and the elastic strain just before fracture; (d) the elastic and plastic strain when loaded at 20,000 lbs; (e) the true stress and true strain at the above loading level. For Material B calculate: (f) the elastic modulus; (g) the strain-at-fracture. 5000 10000 15000 20000 25000 0.1 0.2 0.3 0.4 0.5 0.6 Extension, in Load, lbs A B...
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HW4 - surface of the plate is exposed). How long will it...

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