Abstract
Following up the previous paper on the fracture strength of helically wound composite cylinders under axial tension, the torsional strength is discussed in the present paper.
By making use of the in-plane stress components in each layer of the helically wound laminate under torsional loading, the three-dimensional stress components on the planes containing fibers have been calculated, taking into account the plastic deformation due to the yielding of the matrix or separation between the fibers and the matrix before fracture. And then, by relating these analytical stress components with the fundamental strength which corresponds with the four kinds of fracture mechanism that has been obtained in the authors' experiments on unidirectional fiber-reinforced composites, the torsional fracture strength has been predicted analytically. The fracture is found to be mainly governed by the compressive fracture in the fiber direction in one layer over almost all the ranges of winding angle, exhibiting good agreement with the torsional fracture stresses and fracture behaviors obtained in the experiments on glass-epoxy composites.
The torsional buckling experiments are also carried out on the helically wound thin cylinders in order to ascertain that the above-mentioned fractures are not due to the buckling. The experimental buckling value is about two thirds as large as the theoretical value.
