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Example 43

The cross-section of a turbine rotor disc is designed for uniform strength under rotational conditions. The disc is keyed to a 60 mm diameter shaft at which point its thickness is a maximum. It then tapers to a minimum thickness of 10 mm at the outer radius of 250 mm where the blades are attached. If the design stress of the shaft is 250 MN/m2 at the design speed of 12000 rev/min, what is the required maximum thickness? For steel p = 7470 kg/m3.

Solution

From eqn. (4.22) the thickness of a uniform strength disc is given by t = toe(-^m2a) (1)

where to is the thickness at r — 0. Now at r = 0.25, pco2r2 7470 ( 2tt\2 ,

625 x 10-4

But at r = 0.25, t = 10 mm Therefore substituting in (1),

Therefore at r = 0.03

0 0

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