Stiffness-additive technique for assessment of modal test-article-to-fixture interface flexures

摘要

A method for deriving constrained or fixed-base modes and frequencies from the modes of a structure with springloaded or stiffness-element-loaded boundaries is developed. ^The analytical methodology presented is used to assess the adequacy of test article interface flexure design for a modal test fixture. ^Results show that synthesis of the stiffness-additive mode shapes provides a good measure of the success of interface flexures in simulating the in-service boundary conditions of the test article. ^The method was first tested using a simple beam structure, then applied to the International Space Station Resource Node model. ^Results show that for well-designed interface flexures, using the number of stiffness-additive modes in the synthesis procedure equal to the number of constrained modes one wishes to derive yields good convergence. ^Poor frequency comparison or mode shape correlation can be an indicator that the flexures have undesirably high stiffness in directions that ideally should be unconstrained, or that the stiffness in constrained directions is too low. ^The technique described also has application in multipie-boundary-condition modal testing. ^(Author)