Analysis of deformation and destruction of layered-fibrous composite materials under complex loading

The paper studies effects of postcritical behavior of composites during the occurrence and equilibrium growth of cracks. The experimental study focuses on the influence of additional vibration effects and initial accumulated cyclic damage to the structure on the stability of the deformation processes, postcritical behavior and failure of layered-fiber woven polymer composites, using the example of fiberglass and carbon fiber, which are used in the manufacture of critical structures for various purposes. A comparison of the deformation and failure processes of carbon fiber with reinforcement schemes [0°] and [± 45°] was carried out under tension and torsion of specimens in the form of plates with edge V-shaped notches. Tests of specimens for quasi-static and cyclic tension in the presence of vibrations were carried out using a universal two-axis servohydraulic testing system Instron 8802. Two-stage loading of specimens was implemented: preliminary cyclic tension and quasi-static tension with additional vibrations for torsion. As a result of the tests, loading diagrams of samples with concentrators and initial fatigue cracks were obtained, reflecting elastic-plastic and postcritical deformation and failure. An experimental study was conducted of the influence of the degree of the preliminary cyclic action under tension conditions, as well as the parameters of additional vibrations along the torsion axis on the implementation and length of the descending branch of the deformation diagrams of composite material samples. For a numerical assessment of the implementation of the postcritical deformation stage, the corresponding coefficients were used, which characterize the length of the section of postcritical behavior by the change in stresses and strains. Based on the comparison and analysis of the obtained experimental data, an assessment was made of the influence of additional vibration effects of torsion on the stability of the implementation of the postcritical deformation stage.