Muza - Q5(Friday) - limit(a) will cause the material to...

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Quiz 5 1. True/False a. The main general differences between metals and ceramics are that metals have a higher K 1C , a higher CTE, and higher electrical conductivity. __ True ____ b. Ceramics show no ductility when put under a load. ___ True _____ c. Ceramics are more difficult to form than metals due to the high melting temperatures as well as brittleness.___ True ___ d. Glasses are unique from other ceramics in that they show a long range crystalline order. ___ True ____ 2. Why is porosity much more of an issue when dealing with mechanical properties in ceramics than it is in metals? Because ceramics have a very low K IC compared to metals, the crack size which leads to failure is much smaller than metals by the equation K IC = Yσ(πa) 1/2 . Pores can be considered the same as cracks in that a pore which exceeds the crack size
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Unformatted text preview: limit(a) will cause the material to fail. Since the critical crack length of ceramics is much lower than metals, the amount of porosity must be kept very low to none as to not cause the material to fail. From the equation E = E (1-1.9P+.9P 2 ) it can be seen that the modulus of a ceramic drops as a function of amount porosity. Due to the ductility of metals, the porosity doesnt have this type of effect on the modulus. 2. Alumina(Al 2 O 3 ) ceramic has a density of 3.97 g/cm 3 . Sketch below two stress-strain curves; one for the completely dense and one for alumina which has a level of porosity that reduces the density to 2.5 g/cm 3 . Clearly label which curve corresponds to which ceramic. Fully Dense Less Dense(2.5 g/cm 3 ) Stress Strain...
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This note was uploaded on 04/03/2012 for the course MSE 230 taught by Professor Trice during the Spring '08 term at Purdue University-West Lafayette.

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