Temperature stresses in a cylindrical shell of carbon fibers and the contact problem of heat transfer

Аuthors

Abashev V. M.^*, Demidov A. S.^**, Eremkin I. V.^***, Kiktev S. I.^****, Khomovskii Y. N.^*****

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: abashevVM@mai.ru
**e-mail: demidov@mai.ru
***e-mail: horizont62@yandex.ru
****e-mail: ipk_avm@mai.ru
*****e-mail: yariksp@mail.ru

Abstract

Cylindrical shells are the most common structural elements of rocket engines. When loading by the temperature gradient in radial direction radial temperature stresses occur in them. Such stresses in carbon-carbon shells can be rather dangerous notwithstanding that they are much smaller than the circumferential and axial ones. Moreover, they substantially depend on the thermal conductivity of the carbon fiber material and the shell structure.

The article suggests the equation for the structural thermal conductivity (contact thermal exchange) evaluation of a cylindrical shell in radial direction. When calculating with the equation the carbon fibers' roughness was not accounted for due to the presence of pre-preg matrix, and the shell was divided conditionally through-the-thickness into several layers. The contact forces acting on the fibers were determined based on a primary evaluation of the temperature stresses. The results of the shells' made of carbon fibers calculations with a diameter of 0.02, 0.05, 0.2, 0.5, and 1 mm are presented in the form of tables and graphical dependencies. It is shown, that the elasticity modulus of the first genus of carbon fibers' surface layers can be accounted for in the calculations. It was revealed, that in shells with internal warming-up the specific pressures at the areas of contact spots of the adjoining fibers could reach several tens of kilograms per square millimeter. There is a risk of the carbon fibers structure stratification in the shells with the external warming-up. Thus, we recommend conduct tensile or bending tests with small-sized samples, cut from the shell in radial direction. Tests of such samples should be carried out according to the methodological instructions.

Keywords:

carbon-carbon composite materials, thermal stresses, contact heat transfer, cylindrical shell, thermal resistance

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