Transmission shaft is subjected to a fluctuating torque that varies fr...
Solution:
Given parameters:
- Fluctuating torque = -120 N·m to 500 N·m
- Stress concentration factor = 1.5
- Factor of safety = 2
- Shaft material = C45 steel
Determine the required diameter of the shaft.
Step 1: Calculate the mean torque
- Mean torque, Tm = (500 N·m - 120 N·m)/2
- Tm = 190 N·m
Step 2: Calculate the alternating torque
- Alternating torque, Ta = (500 N·m - (-120 N·m))/2
- Ta = 310 N·m
Step 3: Calculate the maximum torque
- Maximum torque, Tmax = Tm + (Ta/2)
- Tmax = 345 N·m
Step 4: Determine the bending moment
- Bending moment, M = (Tmax * 1000)/2
- M = 172.5 N·m
Step 5: Determine the required diameter of the shaft
- Using the bending moment equation, M = (pi/32) * (sigma_b * d^3), where sigma_b is the bending stress and d is the diameter of the shaft.
- Rearranging the equation, d = (32 * M)/(pi * sigma_b)
- For C45 steel, the endurance limit for bending stress is 150 MPa.
- The maximum bending stress, sigma_b = (32 * M)/(pi * d^3)
- Substituting the values, sigma_b = (32 * 172.5)/(pi * d^3)
- sigma_b = 9.1 MPa
- The required diameter of the shaft, d = (32 * M)/(pi * sigma_b)
- d = (32 * 172.5)/(pi * 9.1)
- d = 46.8 mm
Step 6: Check for the factor of safety
- The factor of safety, FS = (yield strength of material)/(maximum bending stress)
- For C45 steel, the yield strength is 450 MPa.
- FS = 450/9.1
- FS = 49.5
- Since the calculated factor of safety is greater than the given factor of safety, the shaft is safe.
Therefore, the required diameter of the shaft is 46.8 mm.
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