1888. Minimum Weight High Tempterature Joint Design for Reentry Vehicles
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Paper
Abstract
High temperature joint design is a subject which has been receiving increased attention as a result of the ongoing national effort to advance hypersonic and materials technologies. Current fastener technology is sufficient for temperatures below 1600′ F, but the development of advanced carbon/carbon (ACC) has created a need for a robust fastening system which can maintain reasonable strength up to temperatures of 3000′ F. High temperature fastener data is limited, and there is a significant need for additional research and development The objective of this paper is to provide directional input to this future work in the form of minimum weight carbon-carbon splice joint design estimates for a given range of load and temperature conditions. The data presented in this paper is based on an analytical model of a single shear C/C splice joint which was evaluated for running loads ranging from 200-4000 lb/in and temperatures ranging from 78-3000′ F. Minimum weight designs were identified at finite intervals within these ranges through an iterative optimization of the major design variables: fastener material, fastener spacing, fastener diameter, panel thickness, and the number of fastener rows. Sixteen different fastener materials were evaluated in the optimization including among others: T-222 tantalum, C129Y columbium, TZM, carbon/carbon, and tungsten hafnium carbide. The results of this analysis indicate that for joint loads of less than 1000 lb/in and temperatures greater than 1800′ F, the minimum weight design includes C/C as the fastener material. Joints with loads greater than 1000 lb/in and temperatures between 1800 and 2200′ F should be designed using T-222 tantalum or TZM. Tungsten hafnium carbide yields the minimum weight design for joints with loads greater than I 000 lb/in and temperatures greater than 2200′ R. The subject of high temperature carbon-carbon joint design includes many issues, of which weight is only one. Oxidation protection, thermal expansion, and a variety of other material and design problems must be considered in the development of a robust high temperature fastening system for carbon/carbon. This paper represents an effort to quantify the weight impacts of various design decisions, and thereby provide input to the future testing and development of high temperature fastener materials.
