6.1) The following stress condition causes yielding (11 = 690MPa, 12 = 138MPa, 22 = 138MPa ; ). (a) What are the directions and magnitudes of the maximum shear stresses? (b) What is the uniaxial yield stress of the material according to (i) the Tresca condition and (ii) the con Mises criterion?

6.2) An MgO powder compact is prepared by dry pressing of a granulated powder with an average particle size of 0.5 micrometers. The green density is 62% of the theoretical density. The compact is sintered in air at a temperature of 1500C to produce a ceramic that has a 99% theoretical density and an average final grain size of 2 micrometers. (a) If the green compact has a diameter of 2 cm and a thickness of 1mm, predict the fired geometry. (b) Predict how the following changes in the processing will affect the microstructure and the porosity of the polycrystalline ceramic; assume all other process steps are unchanged: (i) The powder has an average particle size of 3 micrometers; (ii) the sintering temperature is reduced to 1300C.