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  • Fiber separation in the reinforcing yarns

    2018-10-26

    Fiber separation in the reinforcing yarns and damages in the yarn matrix may occur during the deformation of flexible woven composite materials due to debonding between the reinforcing fibers and the adhesive. These processes can be described as \'smeared cracks’ [18-21]. This description is based on the changes in the rigidity matrix of the material when a fracture appears. The crack is not introduced explicitly. Fractures can appear only in the composite matrix, while the reinforcing fibers are not destroyed. The following criterion for the fracture of the composite matrix and for a ‘smeared crack’ occurring in the integration node is introduced for taking into account possible internal damages [19]: where is the principal stress function; is the ultimate tensile strength of the material; S is the failure surface determined from the mechanical characteristics of the filler.
    Boundary conditions To model uniaxial tension of the RUC of the flexible woven composite, and the stress and strain fields, the displacement at the A boundary in the tensile direction is forbidden along the warp yarns, while the displacement is given at the B boundary, and the symmetry condition is given at the C and D boundaries. The problem set is solved by the finite xanthine oxidase inhibitors modelling (Fig. 4). The matrix (filler) of the RUC of the flexible woven composite is modeled by the main solid-185 8-node finite elements. These elements allow to model solid bodies in the ANSYS software while taking account of the potential large strains [19]. The reinforcing yarns are modeled by the solid-65 8-node finite elements. These elements allow to take account of the presence of reinforcing elements with the given orientation inside the modeled body and the given volume fraction of the reinforcing fibers. Additionally, it is possible to take into account the emergence and the influence of the ‘smeared cracks’ on the mechanical properties of the material inside the reinforcing yarn matrix. The mechanical properties of the materials used for modeling are listed in Table 1. The resulting stress and strain fields (Figs. 5 and 6) allow finding the most critical areas of fabric yarns interweaving. It is these areas that determine the strength capacities of the material and of the structures created based on it. Fig. 7 shows the results of modeling the object subjected to uniaxial tension by the ‘smeared crack’ method. Analyzing the results presented in Figs. 6 and 7 leads us to the conclusion that the most critical areas of the plain weave are the sloped segments of the reinforcing yarns. Even for materials without pre-existing local damages (reinforcing yarns missing or torn, fabric yarns distorting), the stresses in the sloped weave segments (see Fig. 5) are 4 or 5 times higher than the stresses in the material as a whole. Elastic and elastic-plastic strains also develop primarily in the sloped yarn segments. According to the results shown in Fig. 7, the largest number of smeared cracks emerges in the areas of the maximum stress and strain, which once again proves that overloading the sloped yarn segments is dangerous.
    Conclusion
    Introduction Time redundancy still remains one of the most effective most effective methods for improving the reliability of technical devices, especially of asynchronous automated lines whose technological modules are connected to each other through storage devices. A considerable number of studies [1–7] is dedicated to this problem; the authors of many of these works limit the discussion to finding the availability of the system under consideration. Let us note, however, that a hierarchical approach to constructing models of complex stochastic systems [8–11] is frequently used; such an approach involves having to fit individual elements of the system to one another. For this purpose, it is necessary to know the distribution functions of the mean time to failure and the mean time to repair for these elements. Another drawback of the proposed models is ignoring the reliability of the storage device [12–14], since it significantly complicates the problem. However, when developing models of multiphase systems, functions of the distributions of the mean times between failure and recovery of elements (MTBF, and MTTR, respectively) with time redundancy should be used. In this case, the time reserve should generally depend on the storage device\'s reliability.