Determining the mechanical characteristics of composite materials reinforced with woven preforms

Reduction of the complexity of production of articles from composite materials is largely ensured by the use of reinforcing semi-finished products in which fibers pre-form a framework. Among all the variety of reinforcing systems, woven sleeves (preforms) occupy a special place. The high degree of deformability in a nonimpregnated condition makes it possible to lay this reinforcement on any surface without folds and cuts that provide preservation of strand continuity. This advantage of woven sleeves is accompanied by a change in local reinforcement angles and, consequently, the variable nature of physical and mechanical characteristics of the curved part surface. A method for calculating physical and mechanical characteristics of the composite based on preforms at any point of the part depending on the pattern of laying strands on a curved surface has been developed. The possibility of application of the rod model of the composite to describe physical and mechanical characteristics of the composite material with a woven reinforcement was analyzed. The model essence consists in that the composite is modeled by a diamond-shaped rod system. The rhombus sides serve as fibers and the diagonals as the binder. To verify the theoretical results and substantiate practical recommendations, a series of experimental studies were performed based on the formation of material specimens from two types of woven sleeves with different reinforcement angles. The experimental study program included tensile, bending, and compression tests. A fairly good convergence of theoretical and experimental data was obtained. For example, a square of the correlation coefficient was not less than 0.95 for the modulus of elasticity, not less than 0.8 for the Poisson's ratio, and not less than 0.9 for tensile and compressive strengths. This is the rationale for using the rod model to describe the considered class of composites. The use of the developed procedure will make it possible to increase the perfection of the considered class of designs and obtain rational parameters of the process of their manufacture