고체역학 (Gere) — Torsion: Problem 3.4-12

3.4-12 The bar shown in the figure is tapered linearly from end A to end B and has a solid circular section. The diameter at the smaller end of the bar is \( d_A = 25 \text{ mm} \) and the length is \( L = 300 \text{ mm} \). The bar is made of steel with shear modulus of elasticity \( G = 82 \text{ GPa} \). If the torque \( T = 180 \text{ N}\cdot\text{m} \) and the allowable angle of twist is \( 0.3^\circ \), what is the minimum allowable diameter \( d_B \) at the larger end of the bar?