Machine Design – II ( ME – 308 )

Project # 1 : Design of Shaft and Selection of Bearings

Summary of Class # 2 : Static and Fatigue Analysis

__Step # 1__: Select a material for the shaft.

__Step # 2__: Static Analysis

Static analysis will be done at a location on the shaft where we have either torque or
moment. By using the Maximum shear stress theory and using the equation (18-10) in the
text book, we do static analysis on** diameters d _{3,} d_{2}, d_{4}
**respectively

__Step # 3__: Fatigue analysis

For fatigue analysis, first identify the **critical locations.**

A** critical location **is defined as a point where the shaft is more likely to
fail, such as a Stress concentrated area with a high bending moment. Stress concentration
can occur if there is a sudden change in the cross sectional area (Case 1) or if there is
any non-uniformity (Case 2).

- Diameter d
_{1 }at shoulder – ignore fatigue analysis. Case 1, but low moment. - Diameter d
_{2}at shoulder – perform fatigue analysis ( eqn. 18-28). Case 1 and high moment. - Diameter d
_{2}at keyway – perform fatigue analysis ( eqn. 18-28). Case 2 and high moment. - Diameter d
_{3}at shoulder – perform fatigue analysis (eqn 18-28). Case 1 and high moment. - Diameter d
_{4}at keyway – ignore fatigue analysis (eqn 18-28). Case 2 but low moment.

__ Note: __In eqn 18-28 ignore factor K

S_{e} = k_{a}k_{b}k_{c}k_{d}k_{e }S_{e}^{’}

All the factors can be found out from Chapter 7 in the text book.

You can assume k_{t} for the keyways to be 2.5 and for the shoulders you have
to calculate it from Fig (A-15-9) in the text book.

Notch radius

0£ r £ 0.08 (For sharp corners)

0.08 £ r £ 0.16 ( For rounded corners)

Wherever there is a bearing fitted on to the shaft, the fillet is taken as well rounded and if there is no bearing then the fillet is taken as sharp..

Calculate the notch sensitivity (q) from fig. 5-16.

After the analysis, select the maximum diameters to be the final diameters of the shaft.