Astepped shaft abc consisting of two solid circular segments is subjected to torques t1 = 20,000 lb-in and t2 = 8,000 lb-in acting in opposite directions. the larger diameter of the shaft is d1 = 2.25 in, and the smaller diameter is d2 = 1.75 in. if the radius of curvature at the transition between the larger and smaller diameters is a quarter circle, calculate the maximum shear stress τmax in the shaft.