Ultimate strength of a composite cylinder subjected to three-point bending: correlation of beam theory with experiment

This paper investigates the ultimate bending response of a solid composite cylinder reinforced with uniaxially aligned continuous fibers. Experiments exhibited remarkable nonlinear load–deflections up to failure, indicating that a progressive failure process must have occurred in the cylinder. Thus, the failure of the outmost filament initially subjected to the maximum bending stress does not correspond to the ultimate failure, and additional loads should be still applicable to the cylinder. To reveal this progressive failure process, the cylinder is discretized into a number of parallel layers of different widths. Each layer is considered as a unidirectional lamina, whose overall load component is determined within the framework of classical beam theory. However, the lamina nonlinearity has been incorporated in the analysis using an instantaneous stiffness element defined by the micromechanics bridging model. The benefit of this model is in that only the constituent fiber and matrix properties are required in the analysis. As neither the first ply nor the last ply failure corresponds to the ultimate failure, in addition to the stress failure criterion used to detect the failure of an individual ply another deformation related parameter must be also employed to govern the ultimate failure and then to determine the ultimate strength. In the present case when a 16 layers discretization has been employed, the predicted fourth ply failure strength has been found to work for the ultimate strength and to correlate reasonably well with the experimental counterpart.