7.11 Exercises
259
6. A tubular aluminium shaft having a square cross-section with outside dimension
25 mm must safely carry a twisting moment of 69.5 Nm. Calculate proper wall
thickness t if the working stress in shear is 42 MN/m
2 .
7. Find the torsional moment capacity of a thin-walled square box Section 200 mm ×
200 mm with 5 mm walls if the shear stress is 80 N/mm
2 . Find also the mean
diameter of a circular tube with the same thickness to resist the same twisting
moment and shear stress.
8. A thin-walled box section having dimensions shown in figure is subjected to a
torque of 15 kNm. Calculate the shear stresses developed in each part and the
angle of twist per metre length if G = 84 kN/m
2 (Fig. 7.21).
9. A box section is shown in Fig. 7.22. Prove that for a symmetrical section such
as this, there is no stress in the central web when the tube is twisted. Derive an
expression for the shear stress in the section.
10. An aeroplane elevator has dimensions as shown in Fig. 7.23. Calculate the distribution of shear stresses in the elevator. If the elevator is made of an aluminium
alloy, G = 26.7 kN/mm
2 and is 1524 mm long, what is the total angle of twist.
Fig. 7.21 Thin-walled box
section
Fig. 7.22 Two cell box section
259
6. A tubular aluminium shaft having a square cross-section with outside dimension
25 mm must safely carry a twisting moment of 69.5 Nm. Calculate proper wall
thickness t if the working stress in shear is 42 MN/m
2 .
7. Find the torsional moment capacity of a thin-walled square box Section 200 mm ×
200 mm with 5 mm walls if the shear stress is 80 N/mm
2 . Find also the mean
diameter of a circular tube with the same thickness to resist the same twisting
moment and shear stress.
8. A thin-walled box section having dimensions shown in figure is subjected to a
torque of 15 kNm. Calculate the shear stresses developed in each part and the
angle of twist per metre length if G = 84 kN/m
2 (Fig. 7.21).
9. A box section is shown in Fig. 7.22. Prove that for a symmetrical section such
as this, there is no stress in the central web when the tube is twisted. Derive an
expression for the shear stress in the section.
10. An aeroplane elevator has dimensions as shown in Fig. 7.23. Calculate the distribution of shear stresses in the elevator. If the elevator is made of an aluminium
alloy, G = 26.7 kN/mm
2 and is 1524 mm long, what is the total angle of twist.
Fig. 7.21 Thin-walled box
section
Fig. 7.22 Two cell box section