Design and Realization Of Stress Relief Techniques for Space Craft Components

Abstract

Design and development of space craft components involves combination of different materials. Various materials are joined together by different means like fastening or adhesion bonding to obtain a particular functionality of the component. Such combination of materials with different coefficient of thermal expansion “α”, when subjected to predominant thermal excursions during their working life cycle or fabrication process tend to develop complex thermal stress fields. The developed thermal stress fields in combination with the mechanical constraints lead to the development of various thermo structural stress fields. Under the influence of such thermo structural stress fields the component will tend to deform and deviate from its tolerable design limits, thereby affecting the design functionality and performance of system. This dissertation aims at development of certain design methodologies/techniques to modify the existing mechanical design of space craft components in order to make them relatively insensitive to thermo structural stresses generated during the fabrication process or during operational life. It also focuses on design and realization of similar requirements on two very important spacecraft components called Carrier plate and Multiplexers. The space craft components called Carrier plate assembly is an electronic circuit carrier made of Kovar and carries an Alumina substrate on which a circuit is etched and the Multiplexer (MUX) assembly is a microwave filter consists of precisely machined cylindrical cavity of Invar and the aluminum supporting brackets. The level of thermal stresses generated in the Carrier plate assembly and multiplexer assembly configurations due to the dissimilarity of materials subjected to thermal excursions are evaluated using Finite Element Analysis using CAE tools. The design modifications of the components are evolved using various design tools like topology optimization technique on CAE software packages as well as design intuitions. Various design modifications are evaluated on the basis of environmental constraints, functionality, mass and required space constraints. The selected options for the modifications/ design improvements satisfying various imposed constraints are realized for the purpose of practical measurement of stresses. The modified components are tested and compared with the conventional designs for evaluating the advantages of the design modification in terms of improvement of functionality of components because of the relief of stresses as well for the validation of the Finite Element Analysis results. In a nutshell the dissertation work completely justifies the conceptual models through simulations by CAE tools and the same is evaluated using state of the art measuring methods and at the end gives a robust solution to the conventional problem and makes it almost stress free.