116 



RESISTANCE OF MATERIALS 



FIG. 91 



205. A hollow wrought-iron shaft 9 in. in external diameter and 2 in. thick is 

 required to transmit 600 H.P. with a factor of safety of 10. At what speed should 



it be run ? 



206. A horizontal steel shaft 4 in. in 

 diameter and 10 ft. long between centers 

 of bearings carries a 300-lb. pulley 14 in. 

 in diameter at its center. The belt on the 

 pulley has a tension of 50 Ib. on the slack 

 side and 175 Ib. on the driving side. Find 

 the maximum stress in the shaft, assum- 

 ing that the belt exerts a horizontal pull 

 on the shaft. 



207. An overhung steel crank, like 



that shown in Fig. 88, carries a maximum thrust on the crank pin of 2 tons. 

 Length of crank, 9 in. ; distance from center of pin to center of bearing, 5 in. 

 Determine the size of crank and shaft for a factor of safety of 5. 



208. A propeller shaft 

 9 in. in diameter transmits 

 1000 H.P. at 90 R.P.M. If 

 the thrust on the screw is 

 12 tons, determine the maxi- 

 mum stress in the shaft. 



209. A round steel bar 

 2 in. in diameter, supported 

 at points 4 ft. apart, deflects 

 .029 in. under a central load 

 of 300 Ib. and twists 1.62 

 in a length of 2^ ft. under 

 a twisting moment of 1500 

 f t.-lb. Find E and G for the 

 material. 



210. A steel shaft sub- 



FIG. 92 



E 



jected to combined bending and torsion has an elastic limit in tension of 64,600 

 lb./in. 2 and an elastic limit in shear of 29,170 lb./in. 2 Show that Guest's formula, 



rather than Rankine's, applies to 

 this material. 



211. A shaft subjected to com- 

 bined bending and twisting is made 

 of steel for which the elastic limit 

 in tension is 28,800 lb./in. 2 and the 

 elastic limit in shear is 16,000 lb./in. 2 

 Show that if the bending moment is 



.X^- |*~~ one half the twisting moment, the 



FIG. 93 shaft will be weakest in shear, 



whereas if the bending moment is 

 twice the twisting moment, it will be weakest in tension. 



212. A cast-iron flanged shaft coupling is connected by eight 1^ in. bolts, the 

 axis of each bolt being 6 in. from the axis of the shaft. The diameter of the 



