Answer Happy

Question 3 The contribution of grain-boundary diffusion can sometimes be seen from diffusivity, measurements made on polycrystalline samples of increasingly small grain size. As an example, plot the following data (as In D versus In (grain size)) for the diffusion coefficient of Ni2+ in NO at 480°C, measured as a function of sample grain size. Using the plot, estimate the diffusion coefficient of N2+ in NO at 480 for a 20um grain-size material. Grain Size (um) D (m²/s) 1 1.0x10-19 1.0x10-20 100 1.0x10-21 10

A small pressure vessel is fabricated from an acetal polymer. The stress in the wall is o = (pr/2t) where p is the internal pressure, r is the outer radius of the sphere, and t is the wall thickness. For the vessel in question, r=30mm and t=2 mm. What is the maximum permissible internal pressure for this design if the application is at room temperature and the wall stress is only tensile (due to internal pressurizations that will occur no more than 106 times)? (See Figure 8.21) . Calculate the maximum permissible internal pressure for the design if all conditions are the same except that you are certain there will be no more than 10,000 pressurizations.