Using the information in Problem P1.8, design a composite

torque tube that is 30% lighter than the steel tube but has the same torsional

stiffness. Will the axial stiffnesses of these two tubes be the same?

Problem P1.8

The shear modulus (G) of steel and a quasi-isotropic carbon

fiber epoxy is 78 and 17 GPa, respectively. The mean diameter (D) of a

thin-walled steel torque tube is 25 mm and its wall thickness (t) is 3 mm.

Knowing that the torsional stiffness of a thin-walled tube is proportional to

D3 tG, calculate:

1. Mean diameter of a composite tube that has the same

torsional

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Using the information in Problem P1.8, design a composite

torque tube that is 30% lighter than the steel tube but has the same torsional

stiffness. Will the axial stiffnesses of these two tubes be the same?

Problem P1.8

The shear modulus (G) of steel and a quasi-isotropic carbon

fiber epoxy is 78 and 17 GPa, respectively. The mean diameter (D) of a

thin-walled steel torque tube is 25 mm and its wall thickness (t) is 3 mm.

Knowing that the torsional stiffness of a thin-walled tube is proportional to

D3 tG, calculate:

1. Mean diameter of a composite tube that has the same

torsional stiffness and wall thickness as the steel tube

2. Wall thickness of a composite tube that has the same

torsional stiffness and mean diameter as the steel tube

3. Difference in weight (in percentage) between the steel

tube and the composite tube in each of the previous cases, assuming equal

length for both tubes

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