Exam _3 Solutions

Exam _3 Solutions - Name: _ 1) A metal alloy has the...

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Name: ________________ 1) A metal alloy has the engineering stress-strain curve shown – see next page. A bar of this material is 14 inches long and 2 inches in diameter. a. What load can the bar hold without permanent deformation? [4 points]    lbf 10 * 5 . 1 F in 14 . 3 psi 000 , 480 F A * F in 14 . 3 4 in 2 A psi 000 , 480 6 2 o y 2 2 y b. What length will the bar be when the maximum load is applied (and not released!)? [8 points] The total strain at the maximum load is 0.04   in 56 . 14 l 04 . 0 1 in 14 l 1 l l l l l o o o c. If the load is removed immediately after reaching maximum load, what is the permanent length [8 points] The plastic strain at the maximum load is 0.012    in 168 . 14 l 012 . 0 1 in 14 l 1 l l o
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480,000 psi Plastic strain at maximum load Total strain at maximum load 2
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Name: ________________ 2) Which of these materials has the highest fracture toughness value (circle your answer ) ? Rank order the fracture toughness values of these materials (the highest fracture toughness being 4 and the lowest being 1) . [10 points] (i) steel 4 (~50 MPa * m 1/2 ) (ii) aluminum 3 (~24 MPa * m 1/2 ) (iii) aluminum oxide 2 (~3.0 MPa * m 1/2 ) (iV) polystyrene 1 (~1.0 MPa * m 1/2 ) 3) a. Name and describe the four strengthening mechanisms in metallic materials. [15 poin ts] 1. Mechanism 1 : Grain size reduction Explanation: Smaller grains have more grain boundary area, which prohibit dislocation motion giving the material increased strength. 2.
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This note was uploaded on 04/21/2010 for the course ES 2001 taught by Professor Shivkumar during the Spring '08 term at WPI.

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Exam _3 Solutions - Name: _ 1) A metal alloy has the...

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