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Problem 7 (a) Thin-wall torsion: (i) Using the membrane analogy, obtain graphically a qualitative assessment of the resistance in torsion of the two cross-sections shown in the figure below (assume that the open cross-section remains open at all times, i.e., that the two ends never touch.). (ii) Compute the ratio between the torsion constants of the two cross-sections (using in both cases the corresponding "thin-wall approximations") when the thickness is 1/40th of the inner radius. Does the result correspond to your expectations obtained in part (i)? оо (b) Solid cross-section torsion: Using the Prandtl stress formulation for linearly elastic homogenous and isotropic prismatic beams find the stress and strain state for the torsion problem below of a solid elliptical cross-section beam subjected to a torsion T at either end. Hint: You may find the following results useful in your solution: mba 4 Jab 4 1₁=1/ffx² dx dy = 1-1/y² dx dy "y? - A = - ff dx dy = лab Z 2a X