A circular solid shaft of span L = 5 m is fixed at one end and free at the other end. A twisting moment T = 100 kN - m is applied at the free end. The torsional rigidity Gj is 5000 kNm2 /red. Fllowing statements are made for this shaft.I. The maximum rotation is 0.01 radII. The torsional strain energy is 1 kN-m With reference to the above statements,which of the following applies?
Question
A circular solid shaft of span L = 5 m is fixed at one end and free at the other end. A twisting moment T = 100 kN - m is applied at the free end. The torsional rigidity Gj is 5000 kNm2 /red. Fllowing statements are made for this shaft.I. The maximum rotation is 0.01 radII. The torsional strain energy is 1 kN-m With reference to the above statements,which of the following applies?
Solution
To answer this question, we need to use the formulas for maximum rotation and torsional strain energy in a shaft.
I. The maximum rotation (θ) in a shaft under torsion can be calculated using the formula:
θ = TL/GJ
where: T = applied torque L = length of the shaft G = modulus of rigidity J = polar moment of inertia
Substituting the given values:
θ = (100 kN-m * 5 m) / 5000 kNm2/rad = 0.01 rad
So, statement I is correct.
II. The torsional strain energy (U) in a shaft can be calculated using the formula:
U = T^2L/2GJ
Substituting the given values:
U = (100 kN-m)^2 * 5 m / (2 * 5000 kNm2/rad) = 0.5 kN-m
So, statement II is incorrect.
Therefore, only statement I applies.
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To solve for the maximum torsional stress and the angle of twist, we need to use the following formulas: 1. **Maximum Torsional Stress:** \[ \tau_{\text{max}} = \frac{T \cdot c}{J} \] where: - \( T \) is the applied torque. - \( c \) is the outer radius of the section. - \( J \) is the polar moment of inertia. 2. **Angle of Twist:** \[ \theta = \frac{T \cdot L}{G \cdot J} \] where: - \( T \) is the applied torque. - \( L \) is the length of the section. - \( G \) is the shear modulus. - \( J \) is the polar moment of inertia. ### Step 1: Calculate the Polar Moment of Inertia (J) For a thin-walled closed section, the polar moment of inertia \( J \) can be approximated by: \[ J \approx 2 \cdot A_m \cdot t^2\] where: - \( A_m \) is the mean area enclosed by the midline of the section. - \( t \) is the thickness of the wall. The mean area \( A_m \) can be calculated as: \[ A_m = \text{Perimeter} \times \text{Mean thickness} \] The perimeter of the midline is: \[ \text{Perimeter} = 2 \times (45 - 12.5) + \pi \times (15 - 12.5) \] \[ \text{Perimeter} = 2 \times 32.5 + \pi \times 2.5\] \[ \text{Perimeter} = 65 + 7.85 \approx 72.85 \, \text{mm} \] The mean thickness is: \[ t = 12.5 \, \text{mm} \] So, \[ A_m = 72.85 \times 12.5 \approx 910.625 \, \text{mm}^2\] Now, the polar moment of inertia \( J \) is: \[ J \approx 2 \times 910.625 \times (12.5)^2\] \[ J \approx 2 \times 910.625 \times 156.25\] \[ J \approx 284570.3125 \, \text{mm}^4\] ### Step 2: Calculate the Maximum Torsional StressThe outer radius \( c \) is: \[ c = 15 \, \text{mm} \] The applied torque \( T \) is: \[ T = 500 \, \text{Nm} = 500 \times 10^3 \, \text{Nmm} \] So, the maximum torsional stress \( \tau_{\text{max}} \) is: \[ \tau_{\text{max}} = \frac{500 \times 10^3 \times 15}{284570.3125} \] \[ \tau_{\text{max}} \approx 26.37 \, \text{N/mm}^2\] ### Step 3: Calculate the Angle of TwistThe length \( L \) is: \[ L = 2 \, \text{m} = 2000 \, \text{mm} \] The shear modulus \( G \) is: \[ G = 26 \, \text{GPa} = 26 \times 10^3 \, \text{N/mm}^2\] So, the angle of twist \( \theta \) is: \[ \theta = \frac{500 \times 10^3 \times 2000}{26 \times 10^3 \times 284570.3125} \] \[ \theta \approx 0.134 \, \text{radians} \] ### Summary: 1. The maximum torsional stress developed is approximately \( 26.37 \, \text{N/mm}^2 \). 2. The angle of twist for a 2 m length is approximately \( 0.134 \, \text{radians} \).
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