Find factor of the safety by using mss, de or coulomb mohr theories for ductile materials and bcm or mm for brittle materials (do not use mns), if the shaft is made of the following materials, in this problem based on the material properties you need to decide which failure theory can be used, if more than one theory is applicable choose the one which is less conservative (a). s_yt = s_ye = 42 kpsi, epsilon_f = 0.90 (b). s_yt = 235 kpsi, s_ye = 275 kpsi, epsilon_f = 0.06 (c). grade 20 cast iron with s_ut = 22 kpsi, s_uc = 83 kpsi (d). s_ut = s_uc = 75 kpsi, epsilon_f = 0.045