Flexural Stiffness of Thick Walled Composite Tubes

Abstract

Composite tubes have been used in many applications such as pipes, robot arms, drive shafts, electrical conduits, printing rollers, tube structures for sports equipment, rocket structures, satellite truss structures, landing gears for helicopters, and structural building members etc. For thin wall tubes made of isotropic materials, the flexural stiffness is usually determined by using strength of material approach with the expression EI, where E is the material modulus and I the cross section inertia. For thin walled composite tubes where many layers with different orientations are involved, one may tempt to use the same equation with E replaced by Ex to take care of the fiber orientations. However this may not be correct. Adding to this the increasing thickness of the cylinder, then the inaccuracy of the equation may be even more. By using elasticity approach, an equation for the determination of the stiffness of thick composite cylinders was derived by previous researchers. It was shown by experimental work that the equation based on elasticity provides more accurate results that that based on strength of materials approach. This paper presents some behavior of the bending stiffness of thick walled composite tubes.