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Sample+MT - ,J‘ LOUISIANA STATE UNIVERSITY Mechanical...

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Unformatted text preview: ,J‘ LOUISIANA STATE UNIVERSITY Mechanical Engineering Department Professor Meletis ME 2733 Spring 2004 Midterm Examination Name: (40 P18) 1. State ifthefollowing statementsaretrue ('I')orfalse (F). (a) In general, BCC metals exhibit a ductile-brittle transition. T (b) High fi-acttue toughness requires moderate strength and moderate ductility. T (c) Dislocations require less energy to move in FCC compared to BCC metals. T (d) The BCC metal W is closed packed. T (emmatefialwimadeepepomfial wellhashighmelfingpointbmlowmodulus. T (0 Cr is a BCC metal and;xhibits {iii-Traction for the (31 i) plane. T (g) A screw dislocation is a point defect. T (h) Recrystallization causes an increase in ductility and strength. T (i) Doping Si with A1 creates a p—type semiconductor. T (j) Semiconductors have higher conductivity than metals. T . I. (20 p18) ‘ . 2. A cylindrical metal rod, 5 inches long and with a Imiform cross-sectional area of 0.01 inz, is f loaded in tension. First, a load of2,000 lbs is applied and the rod becomes 5.005 inches long. Whenthe load is released, therod goesbaekto its original lengthofs inches. Themmerod is]oadeda15,0001bsandafterfl1atis mloaded.Afie1-mfloedingthetotal lengthof the rod is 5.01 inches. (:0 Calculate the elastic modulus of the material. (b) Calculate the engineering strain after unloading the rod fi'om 5,000 lbs. (1:) Calculate the true strain after unloading the rod fi-om 5,0001be. ' ((1) Determine the yield strength ofthe material. ' .9" (20m) 3. AsanneyouaddCrmdNto Fetocremiemsolidsolutions:onewitl10.2atomic%Crandfl1e second with 0.2 atomic % N. (a) What type of solid solutions are they? Fe-0.5%Cr: Fe-0.5%N: (b) Compmthedifl’usifitiesofCrinFeandCinFe. Whichoneishigher‘? DCrinFe 01‘ DNinFe (c) What is the meclnnism of diffusion for your selection in (b)? (d) Which solidsolution do you expect to have higher strength? Fe-O.S%'Cr or Fe-0.5%N (e) Do you expect any significant change in the eiasfic modulus of Fe by adding Cr orN? Yes or No in m 9") ‘ 4. The hypothetical metallic elements A and B form the crystal structure shown below. (a) What is the Bravais lattice? (b)HowmanyAandBanmsareassociataedpq-latficepoint? A:_ B: (c} How manyatoms arethere per unit cell? (d)Whatdoyouexpecttheslipsystemtobeforflzis structure? Slip plane: ; Slip direction: (e) Calculate the theoretical density of this material. (Atomic weights A: 340; B: 300) ...
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