This article describes a method for choosing the shape of structurally-similar elements made of polymer composite ma-terials and the scheme of their loading during fatigue tests. These tests are an important step of the complex of efforts to prevent fatigue failure of aviation critical structures made of polymer composite materials. The shape of structurally- similar elements and the loading scheme must be substantiated by a series of preliminary calculations. When testing such samples, the deformation field in the critical zone of the part must be re-produced. The ability to achieve fatigue failure of specimens on the selected equipment shall be verified. The application of the proposed approach to the justification of the choice of structure and loading of structurally similar elements is demonstrated on the example of a typical aircraft structure.

The article describes the results of tests of standard woven and unidirectional polymer composite specimens tested for interlayer shear by the short beam method. Each group of tested specimens has a different thickness, which varies with a certain step. The key features of these tests are described and a comparative analysis of the results obtained is performed. To account for the influence of external factors, tests were conducted under different conditions (standard laboratory conditions, at reduced temperature and moisture-saturated specimens at elevated temperature). On the basis of the obtained data and the performed analysis the diagrams of dependence of the ultimate strength at interlayer shear from the thickness of the specimen were plotted, the diagrams of the range of the obtained values were plotted, the statistical significance was estimated by Student's test and the effect of the cross-sectional dimensions (in this case the thickness) of the standard specimen on the ultimate strength at interlayer shear was determined. To obtain more extensive and reliable data on this problem it is necessary to increase the number of specimens in each of the groups, and conduct repeated tests. The results are recommended for use in tests to determine the interlayer shear strength by the short beam method.

The paper describes the results of a set of statistical data on damage as applied to various structural zones on the application of low-speed impact damage to full-size parts made of polymer composite materials of an aircraft engine to work out the statistics. For this type of work, an installation for application of the required low-velocity impact damage, similar to a pendulum- type copter, has been developed; the developed installation allows application of low-velocity impact damage in a certain range of energies. When performing the work, different zones of the structure (regular shell, flange thickenings, places of thickness change, etc.) were taken into account, the damage was applied taking into account the selected zone. Based on the results of the work, a set of statistical data of applied damage (geometric dimensions, impact interaction characteristics, visual differences) for different structural zones of the structure was obtained, statistical analysis of the obtained test results with determination of average values, standard deviations and variation coefficients of damage depth and maximum diameter was performed. The results of the work are presented in the form of plots of dependences of geometric dimensions of the damage on the actual impact energy. The presented approach to low-velocity impact damage, which is based on the use of full-size structures as test objects, makes it possible to unambiguously determine the required parameters of impact damage to be taken into account when planning the experiment and when substantiating the static and fatigue strength of the structure.