Universal methods for determining the shear modules of composite materials | Mekhanika | kompozitsionnykh | materialov i konstruktsii
> Volume 26 > №3 / 2021 / Pages: 313-326

Universal methods for determining the shear modules of composite materials

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Some of the reasons limiting of the use of composite materials in structural parts have been noted. Among them we can distinguish their relatively low stiffness during interlayer shear and the lack of reliable methods for its establishment. The analysis of the methods used for estimating the modulus of interlayer shear of composite materials has been presented. It has been shown that they are mainly based on the experiments of testing samples for transverse bending with the measurement of deflection under the point of application of the load. The methods are quite labor-consuming, inconvenient in practical use, and do not allow to obtain stable and reliable values of the determined characteristics of composite materials. Modification of some of them by taking into account certain factors affecting the deflection of the sample, such us the curvature of the supports, significantly complicates the process of estimating the interlayer shear modulus. However, the reliability of the determined values is not proven. Three methods have been proposed for determining the shear modules in the three main planes of elastic symmetry of orthotropic composites. For two of them the necessary devices to ensure the simplicity of their implementation and the approach to the strain gauges glued to the sample have been developed. The nature of the distribution of tangential stresses in the sample near the points of application of concentrated forces to it has been considered. Based on this factor, the optimal parameters of samples and their loading schemes have been established. The acceptability of each method has been evaluated by comparing the determined value of the characteristic with its value obtained using another, reliable method. The test has been performed on various types of composite materials. It has been established that one of the proposed methods also allows determining also the interlayer shear modulus of composites. It has been shown that the values of the interlayer shear modulus for orthogonally reinforced composite materials have significantly lower values than the values of the shear module in the plate plane. The advantages of the considered methods have been noted: their universality, convenience and ease of implementation, as well as stability and reproducibility of the obtained values.