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Modal characteristics (natural frequencies and vibration modes) estimation is a common way to avoid resonance vibrations in constructions. It requires reliable data about mechanical properties of the material. In the case, when the polymer composites' determination of such characteristics is difficult (in comparison of isotropic materials), because of a greater amount of elasticity characteristics and their dependency on wide range of structural and technological factors. Also, most of the literature and open sources contain controversial data about composite material properties, and in case of crucial constructions calculations, it would be better to perform an additional experimental identification of these properties. The aim of this paper is to create elastic vibration model parameters identification method for polymer composites using experimental modal analysis. The object of research is laminated carbon fiber-reinforced plastic based on a full strength carbon material widely used in aviation. An experimental determination of natural frequencies and corresponding vibration modes was performed using 3D scanning laser vibrometry. Finite-element analysis was used for numerical determination of modal characteristics. The material model used in calculations is a laminated composite structure with orthotropic, linear, and elastic layers. Identification of parameters was performed as a minimization problem of discrepancy between natural frequencies for corresponding vibration modes obtained numerically and experimentally. The problem solving was performed using a quasi-random search method. The proposed method can be recommended for material properties determination required for a modal analysis of polymer composite structures.

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This paper is devoted to the problems of modeling the vibration behavior of rotors of gas turbine engines. The necessity of modeling their dynamic behavior is caused by their strong influence on the strength characteristics of the engine and its resource. The complexity of solving this problem lies in the fact that the design of modern gas turbine engines has many features that do not allow the use of only one-dimensional models, and the application of three-dimensional models requires a lot of computing resources. Thus, it is suggested to use methods of reduction of finite element models for solving the problems in three-dimensional statement. This paper uses the mode component synthesis (CMS) method to reduce the dimensionality of the rotor model. It also compares the speed of solving modal analysis tasks and determining critical frequencies using complete and reduced models. The quality of reduction is determined. Conclusions about the efficiency of the reduction technique aimed at solving rotor dynamics problems are made.

The use of polymer composite materials for highly loaded structures in modern engineering is constantly expanding, since they have high specific strength characteristics under static loading. However, the question of providing the required resource of such materials under cyclic loading remains open. In this work, we propose an experimental technique for assessing the damageability of specimens of layered polymeric material during fatigue tests. Criteria, which can indicate the appearance of interlayer fracture in the tested specimens, are given. A correlation between the appearance of a new spot of interlayer destruction in the specimens and a decrease in a number of acoustic emission events per unit time, during fatigue tests, were revealed.