Coupling Experiment and Nonlinear Numerical Analysis in the Study of Post-Buckling Response of Thin-Walled Airframe Structures

Abstract

Rational approach to design of load-carrying structures seems to suggest the necessity of focusing special attention on crucial areas of these structures, which are decisive for durability and reliability of the structure. The presence of such crucial areas in a designed solution, resulting usually from its practical functions, should be given careful consideration in view of opportunity to introduce appropriate changes in the design solutions possibly before costly and time-consuming workshop realization of a prototype. The intent of the author is to draw attention to gravity of the factor integrating nonlinear numerical analysis with an experiment – in a broad sense of this word. Then, this chapter presents a methodology that can be used for assessment and current improvement of numerical models thus ensuring correct interpretation of results obtained from nonlinear numerical analyses of a structure. The proposed methodology is based on carrying out experimental examination of selected crucial elements of load-carrying structures parallel with their nonlinear numerical analysis. Special attention is paid to factors determining proper realization of adequate experiments with emphasis placed on the role which the model tests can play as a fast and economically justified research tool that can be used in the course of design work on thin-walled loadcarrying structures. The presented considerations are illustrated by an example structures, whose degree of complexity and deformation range is characteristic for modern solutions in the design of airframe load-carrying structures. As a representative part of the construction design, a fragment of a load-carrying structure containing an extensive cutout, in which the highest stress levels and gradients occur in the conditions of torsion resulting in post-buckling deformation states within the range of permissible loads, was selected. Stress distributions observed within that range of deformation constitute a basis for determination of the structure’s fatigue life. Research described in this chapter were carried out in two stages: In first of them, the objects of research constituted open section cylindrical shells with relatively small diameter in comparison to the length. In this case, the point of analysis was the determination of critical loads values and forms of deformations of free edges of examined structures, which was devoid of reinforcements or reinforced with the stringers.