Andrei V. Malakhov

This paper describes optimization of variable stiffness composite plates (VSCPs) with open-holes under tensile loading. Curved continuous fibers are used to optimize distributions of fiber orientation and the fiber volume fraction during the optimization for the VSCPs. The modeling of VSCPs is performed by means of fiber trajectories, which are aligned in the direction of maximum principal stress. The progressive failure of the VSCPs is modeled by a material property degradation method, taking into account the variable distributions of material properties to predict the ultimate load. It is demonstrated that the ultimate load for the composite plates is increased using the change in a reinforcement structure and a transition from unidirectional to curvilinear reinforcement of fibers. Thus, application of VSCPs with curved fibers compared with unidirectional composites results in more effective use of composite materials in various fields of industry.

This paper analyses the progressive failure of a variable-stiffness composite structure (VSCS). The composite structure is simulated by means of a design method developed earlier. The design method allows curvilinear fibers to be adapted to various geometric discontinuities (holes, notches, etc.) or non-uniform loading. The fiber orientation and fiber volume fraction are heterogeneous in the VSCS. To model progressive failure, a material property degradation method (MPDM) is used. The properties of the composite structure are locally changed due to the nonuniformity in the fiber volume fraction, and the change of the properties is taken into account in the MPDM. A rectangular plate with a hole under tensile loading is modeled, and it is shown that use of the VSCS is more effective than the use of a composite structure with rectilinear reinforcement (orthotropic material) under identical conditions.

The correctness of the algorithm for the plot of rational fiber placement trajectories, assuming their equally stressed state, which is equivalent to the exclusion of shear stresses at the fiber–matrix interface, has been rationalized. An iteration algorithm has been developed for the design of the reinforcement structure of composite plates of a arbitrarily shape with any principles in the change of boundary conditions. As an example, the fiber trajectories that “surround” the hole, which is free or loaded through the steel bushing, have been presented, as well as the trajectories in accordance with a nonuniform distribution of the stresses applied to the plate.