Mike-Nano-Hw6 - ENGRI 111 Homework 6 Due Friday December 2...

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ENGRI 111 Homework # 6 Due Friday, December 2, 2005 1. Draw a stress/strain (engineering) curve for a typical metal and a typical ceramic. For the metal also draw the true stress/strain curve. True Figure 1. The engineering stress-strain curve 2. Answer a - f with true or false and explain your answer with a short sentence. (a) Grain boundaries are created when crystals of different orientations are joined together. -True - The grains of a polycrystalline ceramic or metallic material are crystals joined on different orientations that create interfaces called grain boundaries. (b) In a ceramic the tensile stress is 50 % greater than the yield strength. False -yield strength – point where plastic deformation occurs - Tensile Stress = Force / Cross-sectional Area, it is the state leading up to tensile strength. In a ceramic the point where plastic deformation occurs should be relatively quick as there is almost no elastic deformation (c) Metals are not as brittle as ceramics because there are no cracks present. False - Metals have an electron soup that allows them to move more freely and have the unique ability to bend with the cracks and eventually stop
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them called dislocation. Ceramics do not have this ability and cracks will eventually destroy the object. (d) Ceramics are brittle because there are no dislocations present. True- there are very few available slip systems for dislocations to move, and so they deform very slowly.
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  • Fall '05
  • GIANI
  • Tensile strength, carbon nanotubes, Short sentence, gauge length, False -yield strength, true stress/strain curve

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