(c) circular tube as (a) but with additional four rectangular fins 80 mm long by 15 mm wide symmetrically placed around the tube periphery.

All sections have the same length of 2 m and G = 80 GN/m2 [0.039 rad; 0.088 rad; 0.038 rad]

To what maximum torque can sections (a), (b) and (c) be subjected if the maximum shear stress is limited to 100 MN/m2? [4.8 kNm; 3.24 kNm; 5.7 kNm]

What maximum angle of twist can be accepted by tube (c) for the same limiting shear stress? [0.0625 rad]

5.18 (B). Figure 5.20 shows part of the stirring mechanism for a chemical process, consisting of a circular stainless-steel tube of length 2 m, outside diameter 75 mm and wall thickness 6 mm, welded onto a square mild-steel tube of length 1.5 m. Four blades of rectangular section stainless-steel, 100 mm x 15 mm, are welded along the full length of the stainless-steel tube as shown.

(a) Select a suitable section for the square tube from the available stock list below so that when the maximum allowable shear stress of 58 MN/m2 is reached in the stainless-steel, the shear stress in the mild steel of the square tube does not exceed 130 MN/m2.


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