Investigation of Bolt Preload Relaxation for JWST Thermal Heat Strap AssemblyJoints with Aluminum-1100 and Indium Gaskets

摘要

Accurately predicting fastener preload relaxation in the James Webb Space Telescope (JWST) heat strapassemblies is essential to insure adequate thermal performance during its mission lifecycle. Themechanisms for preload relaxation in the strap joints include Al-1100 material creep, indium gasket flowout,and embedment of the joint faying surfaces. This report documents the results from a bolted jointrelaxation test, including analysis and curve fitting of the test data for predicting preloads five years afterinitial torque application. The report also includes the derivation of a preload uncertainty factor envelopingboth torque/preload application scatter and expected preload relaxation at the end of mission life.