Stress Fields in Fiber Reinforced Laminate Beams Due to Bending and Torsion Moments

A model of fiber reinforced composite laminate beam with sections of orthogonal shape is presented, in which the stresses due to simultaneously applied torsional and bending moments are found by an analytical solution. The technique followed is based on Sokolnikoff ’s approach in conjunction with the theory of anisotropic elasticity. The results derived permit the evaluation of the off-axis-strength elastic constants for the material. The evaluation of 3-D stress distributions in beams with sections characterized by various aspect ratios reveals variations of stresses, which depend on the warping combined with flexure in these laminate composite beams. In addition, useful information gained from the study of variation of the elastic properties as well as torsional rigidity for fiber reinforced laminate beams leads to further knowledge for the profile of stress distribution allover the beam. Specifically, the results have revealed that the torsional rigidity of the fiber reinforced laminate composite beam reaches an optimal value at a -lamination angle between 20° and 30°. Thus, the normal stresses vary in higher values versus the lamination angle of the composite than the shear stresses do. Also, the stresses allover the beam become so intensive as the bending-to-torsion moments ratio increases.