In this study, three shafts made of composite materials with different cross sectional geometries are considered. The first shaft consists of two solid cylindrical sections of different radii resulting in a stepped cross section. The second shaft has the shape of a truncated cone and it is also solid. The third shaft is hollow and it has three sections, with a short truncated conical section connecting the two cylindrical sections of different radii. The shafts are made of glass fiber reinforced composites. For the first shaft with stepped cylindrical cross section, the fiber reinforcement is of fabric type, whereby the assumption of isotropy is valid. On the other hand, the second and third shafts are made of glass fiber reinforced composites with straight wound string type fiber glass as reinforcement. In this case, the orthotropy of the material is taken into consideration in the numerical analysis. The shafts are assumed to be fixed at one end, and a torque to be applied statically at the free end. The purpose is to obtain the stress distribution along each shaft numerically, and to compare the numerical results with those obtained from our experiments. The material is assumed to be linearly elastic and the rotations to be small. The finite element method is employed in the numerical analysis. A particular overall stiffness matrix for the entire shaft was obtained by applying a stress functional, phi(r,z), to the unit element of the medium. Triangular elements were used in the numerical model. To validate the mathematical model the stress distribution in each shaft is also obtained experimentally. The shafts were manufactured in our laboratories using epoxy or polyester resin with fiber glass reinforcers. The hollow shaft was manufactured in two versions; namely, one with a winding angle of 45 degrees and the other with an angle of 60 degrees. The volume of the isotropic shaft consisted of 18% reinforcement and 82% polyester. On the other hand, the orthotropic shafts had 60% reinforcer and 40% resin. The actual stresses produced in the sample shafts by the external torques were experimentally measured by means of strain gauges. Comparison of the experimental results with those obtained theoretically has shown an agreeable difference level of 7% on the average, depending on the geometry and the composition of the shaft. The comparative results are given below.

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