ts2201f09

# ts2201f09 - EMSE 201 Introduction to Materials Science...

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EMSE 201 — Introduction to Materials Science & Engineering 4 November 2009 Name: SOLUTION Department of Materials Science and Engineering 1 of 7 Case Western Reserve University Test #2 — 75 minutes; 100 points; 6 questions; 7 pages; 10% of course grade Partial credit will be given for correct set-ups and reasoning. Give units on numerical answers where appropriate and use the correct number of significant figures. Please write all answers on these pages; use the backs if needed. 1) (10 points) A tensile stress is applied to a single-crystal fiber of Al 2 O 3 . The fiber is oriented such that the applied stress σ , the long axis of the fiber, and the c -axis of the crystal are all parallel (see sketch). Three possible slip planes for Al 2 O 3 , and their normals, are illustrated below: plane 1, parallel to the c - axis; plane 2, neither parallel nor perpendicular to the c -axis; and plane 3, perpendicular to the c -axis. On which slip plane(s) will the resolved shear stress be highest ? On which slip plane(s) will the resolved shear stress be lowest ? Explain . τ r = cos( φ ) cos ( λ ) (3 pts) For plane 1, cos( ) = cos(90°) = 0 = 0 (1 pt) For plane 3, cos ( For planes 1 and 3, will be lowest (2 pts) For plane 2, 90°, and will be 90° only in special orientations, so cos( ) (the Schmid factor) will in general be non-zero (2 pts) For plane 2, will be highest (1 pt) 2) a) (8 points) Circle the one word in each set of parentheses that correctly completes the sentence. i) For a given semicrystalline polymer, e.g. polyethylene, tensile strength increases with ( increasing , decreasing) molecular weight and ( , decreasing) crystallinity. ii) In a metal eutectic system, the ( highest , lowest) strength occurs near the eutectic composition. iii) ( Edge , Screw) dislocation lines move parallel to the direction of slip; (edge, screw ) dislocation lines move perpendicular to the direction of slip. b) (5 points) Rank the following steel phases or microstructures from highest ductility (1) to lowest (3): _ 3 _ martensite _ 1 _ spheroidite _ 2 _ tempered martensite. Partial credit: 3-2-1: 3 pts ; 2-1-3: 3 pts ; 1-3-2: 2 pts ; 2-3-1: 1 pt ; 1-2-3: 1 pt . ! ! plane 1 (|| c) plane 2 (not || c, not c) plane 3 ( c) " " c

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EMSE 201 — Introduction to Materials Science & Engineering 4 November 2009 Department of Materials Science and Engineering 2 of 7 Case Western Reserve University 3) Use the graphs on the next page to answer the following questions. a) (1 point) A steel of eutectoid composition is held at 760 °C until its micro- structure consists of a single phase. Give the “-ite” name of that phase. austenite b) The alloy of part a) is then cooled in less than 0.5 s from 760 °C to 675 °C (1250 °F) and held at this temperature. See the blue lines on the isothermal transformation diagram, next page. i)
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## This document was uploaded on 11/08/2011.

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ts2201f09 - EMSE 201 Introduction to Materials Science...

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