Capillary impregnation of a semipreg stack in composite aircraft parts production

Aeronautical and Space-Rocket Engineering


Аuthors

Fedyaev V. L.1*, Khaliulin V. I.2**, Sidorov I. N.2***, Kataev Y. A.2****

1. Institute of Mechanics and Engineering - Subdivision of the Federal State Budgetary Institution of Science “Kazan Scientific Center of the Russian Academy of Sciences” , Kazan, Republic of Tatarstan, Russia
2. Kazan National Research Technical University named after A.N. Tupolev, 10, Karl Marks str., Kazan, 420111, Russia

*e-mail: vlfed2020@gmail.com
**e-mail: pla.kai@mail.ru
***e-mail: insidorov1955@mail.ru
****e-mail: YuPKataev@kai.ru

Abstract

The reinforcing filler impregnation by the binder is one of the basic stages while aviation and rocket engineering composite structures production by the vacuum molding method. The porous space in the reinforcing filler, such as woven, consists of super-capillary (large) pores, formed by the fibers, and micro-capillary pores, formed by the micro fibers inside the fibers. The impregnation time is being determined by the speed of the inter-fiber capillary filling by the filler. Its study is being performed with the mathematical modeling methods. Accounting for the fact herewith that the woven filler consists of fibers, which in their turn, are formed by the continuous mono-fibers, the filler capillary movement occurs both along the fibers in capillary tubes and transversally in the capillary slits. As long as the shape of the real capillary walls is rather complex, it is being idealized, and the tubes are being replaced by the equivalent ones in the form of a circular cylinder with slits. Besides, it is assumed that physical and chemical properties of the internal surface of these tubes are identical to those of filament surfaces.

As the result of the Laplace’s equation integrating, employing expressions for estimating the pressure in the quiescent filler in the entry of the tube and transversal motion of the filler in the capillary slits, the authors obtained expressions allowing estimating the resin flow rate in the tubes and the time of their filling. The article demonstrates that the filling rate of the capillary tubes decreases over time. It can be increased by reducing the resin flow from the tubes through the slits, increasing the equivalent radius of the tubes within certain limits, for example, by reducing the loads acting on the surface of the semipreg stack, as well as by viscosity reducing of the polymer resin, and performing impregnation at higher temperatures.

The resin flow in the capillary slits in the transverse direction is in many ways similar to the resin flow in capillary tubes. However, in this case, the resin flows both in the capillary tubes and in the gaps between the sections of the micro-filberes surfaces. Provided that this flow is similar to the liquid filtration in the fractured-porous media, an equation for determining the time-dependent dynamics of the resin flow in the gap, the surface tension coefficient, the contact angle, the average distance between the slit walls, their roughness, and the resin viscosity was obtained.

Recommendations on the semipreg stack capillary impregnation intensification and its time reduction are presented based on the mathematical modeling results.

Keywords:

composites, semipregs, vacuum molding, capillary impregnation, composite porosity, preform permeability, semipregs impregnation modeling, impregnation time computing

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