Damages accumulation in composite panels under low-cycle loading

DOI: 10.34759/vst-2023-2-84-90

Аuthors

Akulin P. V.

PJSC UAC Sukhoi Design Bureau, 23A, Polikarpova str., Moscow, 125284, Russia

e-mail: plus-orange@yandex.ru

Abstract

There are requirements for the resource strength of aircraft in the aviation industry. It is necessary at present to perform costly and lengthy full-scale tests to meet the said requirements, virtual tests are being implemented hereupon. Just now, techniques for the resource computation require extra studying and incapable of replacing completely the full-scale tests.

The presented article is studying the accumulated damages in composite materials at the low-cycle cantilever bending. The full-scale experiment on cantilever bending of a structurally congruent flexible element is adduced. Residual deformations were being observed on the samples after the load was removed. The hypothesis on the residual deformations origination due to the cracks formation in the transversal layers of a composite material is being put forward. The majority of the known works on the said subject [1-9] consider behavior of the simplest plates. The presented article studies a flexible element from a composite material with complex physical and geometrical characteristics.

The object of the study is a structurally congruent flexible element from the composite material, which serves as an overlay between the tail part of the wing and lift devices. This element is being installed in preload and deformed, tracking the deviations of lift devices, being in constant contact with it. This allows hiding the gap between the tail section of the wing and the lift devices, creating thereby a continuous aerodynamic contour. In the works [10-11], various designs, in which a closed loop is implemented between the wing and the lift devices in various deflection modes, are presented.

The author solved the following tasks:

1. The cantilever bending calculation of a structurally congruent flexible element in a geometrically nonlinear formulation by the finite element method. The finite element model employs three-dimensional (volumetric) elements. The monolayer of the composite package was modeled into one element by the height. The model is fixed on the end face over all degrees of freedom. The stop was modelled in the form of а cylinder, to which a hard loading was applied in the form of the vertical displacement. All remaining degrees of freedom of the stop member were prohibited. A contact was applied between the structurally congruent flexible element and the stop.
2. Identification of theoretical calculations based by the full-scale experiment results.
3. Analytical calculation of the composite material package stiffness characteristics degradation. The process of micro-defects accumulation is assumed to be mostly a corollary, which is being regulated by physical thermodynamic laws, based on the entropy approach [12-15]. Micromechanical approach [16-19] is being used to associate the material damage with its appropriate properties and exact description of the degradation effect. A technique for the composite material properties degradation computing is described in [20].

The obtained results of the package stiffness characteristics degradation demonstrated a behavior similar to the full-scale experiment. Based on the obtained results, the inference may be drawn that the hypothesis on the cracks origination in the transversal layers of a composite material describes the material behavior

Based on the data obtained, it can be concluded that the hypothesis of the occurrence of cracks in the transversal layers of the composite material describes the behavior of the material quite acceptably.

Keywords:

properties degradation, damage accumulation, layered composites, transversal cracking

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