STRUCTURAL RESPONSE OF COMPRESSION-LOADED, TOW-PLACED, VARIABLE STIFFNESS COMPOSITE PANELS

Abstract Results of an analytical and experimentalstudy to characterize the structural response oftwo compression-loaded variable stiffness com-posite panels are presented and discussed.These variable stiffness panels are advancedcomposite structures, in which tows are laid downalong precise curvilinear paths within each plyand the fiber orientation angle varies continuouslythroughout each ply. The panels are manufac-tured from AS4/977-3 graphite-epoxy pre-pregmaterial using an advanced tow placement sys-tem. Both variable stiffness panels have the samelayup, but one panel has overlapping tow bandsand the other panel has a constant-thicknesslaminate. A baseline cross-ply panel is also ana-lyzed and tested for comparative purposes. Testsperformed on the variable stiffness panels show alinear prebuckling load-deflection response, fol-lowed by a nonlinear response to failure at loads* Aerospace Engineer, Vehicle Analysis Branch.t Professor, Departments of Aerospace and OceanEngineering, and Engineering Science and Mechanics,Associate Fellow AIAA.§ Senior Engineer, Structures and Materials Compe-tency, Fellow AIAA.Copyright ©2002 by the American Institute ofAeronautics and Astronautics, Inc. No copyright isasserted in the United States under Title 17, U.S.Code. The U.S. Government has a royalty-free licenseto exercise all rights under the copyright claimed hereinfor Governmental Purposes. All other rights arereserved by the copyright owner.between 4 and 53 percent greater than the base-line panel failure load. The structural response ofthe variable stiffness panels is also evaluated us-ing finite element analyses. Nonlinear analyses ofthe variable stiffness panels are performed whichinclude mechanical and thermal prestresses. Re-sults from analyses that include thermal prestressconditions correlate well with measured variablestiffness panel results. The predicted response ofthe baseline panel also correlates well with meas-ured results.