An Approximate Analysis of the Inner Wall Loading of a Bimetallic Camera Shell of Reusable Rocket Engine

• Main Authors: V. S. Zarubin, V. N. Zimin, G. N. Kuvyrkin
• Format: Article
• Language: Russian
• Published: MGTU im. N.È. Baumana 2016-12-01
• Series: Aèrokosmičeskij Naučnyj Žurnal
• Subjects: engine combustion chamber; bimetallic shell; ideal elastic-plastic medium; short-term creep
• Online Access: https://aerospace.elpub.ru/jour/article/view/41

Various technical devices quite widely use bimetallic shells as the structural elements. A chamber combustion design of the liquid rocket engine (LRE) is a typical use of the bimetallic shells.In LRE operation a combustion chamber shell is subject to intense thermal and mechanical effects, which necessitates cooling. A cooling shell path is formed by a gap between its inner and outer walls connected to each other by milled or grooved spacer ribs. The outer wall of the shell serves as a load-bearing element, the inner wall is in direct contact with high-temperature combustion products and exposed to intense heat. The difference in functions of shell walls calls for their manufacturing from different materials with different thermophysical and mechanical properties.Interaction between the shell walls of different materials in heating and cooling leads to emerging thermal strains of various values in the walls. In terms of mechanical properties the inner wall material, usually ranks below the outer wall material strength, which uses the high strength stainless steel 12Х21Н5Т. The inner wall is typically made from copper-based highly heat-conductive alloys. (eg.: chromium bronze). Therefore, the result of the difference in temperature deformations, arising in the walls,  is inelastic nonisothermal strain of the inner wall material with (usually) elastic behavior of the outer wall material.For reusable LRE, a cyclic sequence of the loading steps of the inner wall can lead to accumulating damages in its material because of the low-cycle fatigue and cause destruction of the wall or the loss of the cooling tract tightness. The main parameter that determines the level of low-cycle fatigue, is an absolute value of the accumulated inelastic strain (both plastic and evolving over time creep deformation). Quantitative evaluation of this parameter involves analysis of the inner wall loading with multiple starts and shutdowns of LRE. The paper represents an approximate analysis of such loading under certain simplifying assumptions using the approaches typical for mathematical modeling of structures under thermal stress.