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Material Science

Material Science - Name 1 A metal alloy has the engineering...

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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] lbs F in psi F A F in in A psi o y y 6 2 2 2 10 * 5 . 1 14 . 3 000 , 480 * 14 . 3 4 2 000 , 480 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 of the bar? [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 (ii) Polyester 1 (iii) Aluminum 3 (iv) Silicon carbide 2 3) a. Name and describe the four strengthening mechanisms in metallic materials. [15 points] 1. Mechanism 1 : Grain size reduction Explanation: Smaller grains have more grain boundary area, which prohibit dislocation motion giving the material increased strength. 2. Mechanism 2 : Solid solution strengthening Explanation: When impurities are introduced into the parent lattice, a certain amount of strain is also added. Lattice strain field interactions between dislocations and these impurity atoms result, and consequently, dislocation movement is restricted. This will increase the strength of the
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