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mat33hw7 - strain reactions are usually repulsive which...

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Mat. 33 Homework # 7 3/23/09 1) A) In solid-solution strengthening the concentration of impurity is increased by alloying with impurity atoms that go into either substitutional or interstitial solid solution, which result in an increase of both tensile and yield strengths. B) I do not think that the same strategy would be as effective for polymers because it is not always the case with polymers that the pure element is weaker as it is with metals, therefore I think that solid-solution strengthening could work with some polymers but it may be possible that it would have the opposite effect on other polymers. 2) During the recrystallization of a cold worked metal the dislocation density increases with deformation due to the formation of new dislocations. Therefore the average distance between dislocations decreases. Dislocation-dislocation
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Unformatted text preview: strain reactions are usually repulsive, which causes the motion of a dislocation to be hindered by the presence of other dislocations. As dislocation density increases this resistance occurs at a greater scale and results in the drop in yield strength. 3) A) (delta)G = a 3 (delta)G V + 6a 2 y d(delta)G/da = 3a 2 (delta)G V + 12ay 0 = 3a 2 (delta)G V + 12ay a* = -4y/(delta)G V (delta)G* = (a*) 3 (delta)G V + 6(a*) 2 y = 32y 3 /((delta)G V 2 ) B) (delta)G* is greater for a cube because cubes have a higher surface to volume ratio when compared to spheres. 4) At this minimum Brinell hardness the tensile strength = 800 MPa, which would require a deformation of at least 13%CW. If the steel is cold worked to the level then the ductility would reach 15%EL, so it is possible to have steel at both of those values instantaneously....
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