1. The problem statement, all variables and given/known data Question Assuming the torque and maximum shear stress values to be the same for both shafts, determine the size of a suitable soild shaft which could be used instead of the hollow shaft. Information/Data Known Firstly, a previous question - A ship's propellar shaft transmits 7.5MW at 440rev/min. The shaft has an external diameter of 230mm. Calculate the maximum permissable bore diameter if the shearing stress in the shaft is limeted to 150MN/m^2. The modulus of rigidity for the shaft material is 79GN/m^2 Ok, the following is known: Bore Diameter = 108mm = 0.108m DH = Hollow shaft External Diameter = 0.23m touH = touS TH=TS 2. Relevant equations T/J = tou/r = Gθ/l We're using T/J = tou/r J=pi(D^4-d^4)/32 [Hollow Shaft] J=pi(D^4)/32 [Soid Shaft] 3. The attempt at a solution Ok so to show understanding, the question says that the torque and stress values are the same for both shafts therefore: touH = touS TH=TS Which means we need to find JS, rS, JH and rH JS/rS = JH/rH We can find our H values but not our solid so: JH = pi(DH^4 - dH^4)/32 DH = 0.23m dH = 0.108m JH = 2.6138x10^-4m^4 rH = D/2 = 0.115m JS = pi/32 [because we can only assume DS atm is equal to 1] JS = 0.0982m^4 rS = D/2 = 0.5Dm Back to the equation: JS/rS = JH/rH Muliply over: JH(rS)/JS(rH) Which looks like so: (2.6138x10^4)x0.5 / 0.0982 x 0.115 = d^3 = 11.5727x10^-3 to get the diamter, we cube route the answer: (cube root)11.5727x10^-3 = D D = 0.226m Therefore the diameter of the solid shaft use to replace the hollow shaft is: 226mm What i'm asking for here is clarification that what i've just done here is correct. I've been told by my collegues that i may have gotten the bore diamter wrong, someone said they got 198mm instead of 108mm. So from the second question i have typed out p above, could you find the time to check if i have the correct or incorrect bore diamter and the second request is simply to read the above (my workings out) to see if it looks / is valid. Thankyou for your time, i really do appreciate your help even if it's a simple word.