ASME Shaft Design Standards and Calculations
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ASME Code for Design of Shafts
The ASME (American Society of Mechanical Engineers) code provides standard guidelines for calculating the safe diameter of a shaft subjected to different types of loads. The code considers combined effects of bending moment, torsional moment, shock, and fatigue.
ASME Shaft Diameter Determination
According to the ASME code, the shaft diameter is determined using the following formula:
$$d = \left( \frac{16}{\pi\,\tau_{allow}} \sqrt{ (K_b M_b)^2 + (K_t T)^2 } \right)^{1/3}$$
Formula Variables:
- $M_b$ = Bending moment
- $T$ = Torque
- $\tau_{allow}$ = Allowable shear stress
- $K_b$ = Shock and fatigue factor for bending
- $K_t$ = Shock and fatigue factor for torsion
ASME Recommended Allowable Stresses
The allowable shear stress ($\tau_{allow}$) recommendations are:
- For a shaft without a keyway:
$\tau_{allow} = 0.30 \, \sigma_{yt}$ or $\tau_{allow} = 0.18 \, \sigma_{ut}$ - For a shaft with a keyway:
The allowable stress is reduced by approximately 25%.
Purpose of ASME Code in Design
- Ensures safe and reliable shaft design.
- Accounts for dynamic, shock, and fatigue loading conditions.
- Provides a standardized method utilized across various industries.
Machine Design Assessment Questions
1) Which of the following is NOT a traditional design method?
Answer: d. Rapid prototyping
2) Poor ergonomic design may lead to:
Answer: b. User discomfort
3) Cotter joints are commonly used for:
Answer: a. Connecting rods under axial loading
4) Factor of safety in a static loading condition is:
Answer: b. Permissible stress / Maximum stress
5) The stresses induced in the cotter of the cotter joint are:
Answer: c. Shear and bending stress
6) Torsional rigidity of a shaft refers to its ability of:
Answer: c. Resisting twisting moments
7) The key fits in the keyway of the:
Answer: c. Both shaft and hub
8) Use of multiple notches in a V-shaped flat plate will:
Answer: b. Increase the stress concentration
9) Which of the following line is the safest in machine design?
Answer: b. Soderberg line
10) If a spring has plain ends, the number of inactive coils is:
Answer: a. 1
11) Maximum efficiency of a square thread is:
Answer: a. (1 – sin$\theta$) / (1 + sin$\theta$)
12) Minimum specified length of fillet weld is:
Answer: b. Four times the size of weld