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 d3, d2, d4 respectively. We assume the diameter d1 = 0.8 (d2).
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).
Note: In eqn 18-28 ignore factor Kf in the numerator.
Se = kakbkckdke Se
All the factors can be found out from Chapter 7 in the text book.
You can assume kt 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.
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.