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ENGRI_HW7_2007 - a mismatch in the coefficients of thermal...

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ENGRI 111 Homework # 7. Due Monday, Dec. 3, 2007 (by 5:00 PM) 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. 2. Answer a - k 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. (b) In a ceramic the tensile stress is 50 % greater than the yield strength. (c) Metals are not as brittle as ceramics because there are no cracks present. (d) Ceramics are brittle because there are no dislocations present. (e) The mechanical response of polymers is temperature dependent. (f) Metals containing nanograins are much stronger than those containing larger micron size grains. (g) Ceramics can never be toughened. (h) Thermal expansion is due to the asymmetric nature of the potential energy vs. interatomic distance plot. (i) Many films deposited on substrates develop tensile or compressive stresses because of
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Unformatted text preview: a mismatch in the coefficients of thermal expansion of the film and of the substrate. (j) Nanoindentation is a convenient way to probe the mechanical response of nanostructures. (k) Nanoindentation techniques rely on measuring continuously the applied load and the area of the indentation in the sample. 3. The following data were collected from a 0.4-in.-diameter test specimen of polyvinyl chloride. The gauge length is the length of the specimen that is changing due to the load. After fracture, the gauge length is 2.09 in. and the diameter is 0.393 in. Plot the data as stress vs. strain and calculate: a) the 0.2% offset yield strength b) the tensile strength c) the modulus of elasticity d) the % elongation (=the strain x 100 for the gauge length after fracture) Load (lb) Gauge Length (in) 2.00000 300 2.00746 600 2.01496 900 2.02374 1200 2.032 1500 2.046 1660 2.070 1600 2.094 1420 2.12...
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