A METHODOLOGY TO INVESTIGATE THE INFLUENCE OF THE FILLET RADIUS ON THE BUCKLING OF INTEGRALLY STIFFENED PANELS

Abstract

THE USE OF INTEGRALLY STIFFENED PANELS (ISP'S) IN WINGS OF SMALL AND MEDIUM-SIZED AIRCRAFT IS FREQUENT IN AVIATION AND, ALTHOUGH THE FINITE ELEMENT METHOD HAS BECOME AN IMPORTANT TOOL FOR ENGINEERS TO OBTAIN THE BUCKLING LOAD OF THESE STRUCTURAL MEMBERS WHEN SUBJECTED TO COMPRESSIVE LOADING, SOME RESULTS BASED IN CHARTS PUBLISHED BY NACA FOR CALCULATION OF THE CRITICAL COMPRESSIVE STRESS OF IDEALIZED STIFFENED PANELS ARE STILL USED IN THE PRELIMINARY STAGES OF THE WING DESIGN IN MANY AIRCRAFT COMPANIES. HOWEVER, SUCH CHARTS CONSIDER SIMPLE GEOMETRIES AND NEGLECT GEOMETRIC DETAILS AS THE FILLET RADIUS USED IN THE CURRENT DESIGN OF ISP'S. THE OBJECTIVES OF THIS PAPER ARE TWOFOLD: (I) TO SHOW THAT THE CHARTS PUBLISHED BY NACA PROVIDE GOOD RESULTS FOR THE CRITICAL BUCKLING STRESSES FOR SEVERAL GEOMETRIES OF ISP'S, WHEN COMPARED TO FINITE ELEMENT RESULTS WITH PROPER BOUNDARY CONDITIONS, PROVIDING FILLET RADIUS ARE ALSO NEGLECTED IN THE FINITE ELEMENT MODELS AND (II) TO SHOW THAT THE VALUES OF THE CRITICAL BUCKLING STRESSES FOR LOCAL INSTABILITY OF ISP'S MAY BE SIGNIFICANTLY INCREASED WHEN ONE CONSIDERS THE EFFECT OF THE FILLET RADIUS, MEANING THAT THIS PARAMETER SHOULD ALSO BE CONSIDERED IN THE OPTIMAL DESIGN OF SUCH STRUCTURES. SEVERAL NUMERICAL RESULTS OBTAINED WITH FINITE ELEMENT SIMULATIONS BASED ON DIFFERENT GEOMETRICAL PARAMETERS OF ISP'S ARE ALSO PRESENTED IN THIS STUDY.