Study On Dynamic Modeling Of Bolted Flange Connections In Aerospace Structures

Since its simple configuration and reliable operation, bolted flange joints are widely used in industrial structures. However, due to the multiple nonlinearities at the connecting interface, behaviors of this connection are complex in nature. In this dissertation, to build efficient dynamic models for the aerospace structures assembled by bolted flanges, dynamic modeling for rocket sections using Timoshenko beam models, static behaviors and mechanism of dynamic response for the joint are thoroughly studied. A simplified dynamic model for bolted flange connections is proposed and validated, which is, then, applied in the dynamic modeling and analysis for a launch vehicle.Main works of this dissertation are:1. Through the comparison between Benoulli-Euler beam theory and Timoshenko beam theory, the modeling strategy for rocket sections using Timoshenko beams is proposed, which introduces shear deformation under lateral forces, and the method to determine the equivalent stiffness for this model is established. Then, the proposed method is applied in dynamic modeling for a stringer-skin cylinder structure. Numerical results validate the efficiency of the proposed model and its priority to the Benoulli-Euler beam model.2. The static nonlinear behaviors of bolted flange joints are studied, through which its different axial stiffness in tesion and compression are revealed. Accordingly, an analytical model for the axial response of bolted flange is proposed, which consists of a bending beam and a spring. Then, parameter impacts on the joint on the joint stiffness are discussed. Besides, axial displacement of the connected structure subjected to transverse loads is investigated and theoretically explained.3. To represent the different tensile and compressive stiffness of bolted flange joint, bilinear springs are employed, and a schematic dynamic model with2DOFs is developed. Through the zone division of the motion plane, the dynamic responses of the schematic model are analytically derived, and a recursion and dichotomy algorithm is constructed to obtain avoid numerical dissipation. A special type of dynamic behavior under transverse impact, coupling vibration of transverse and longitudinal directions, is observed. Furthermore, the extracted force response at the connecting interface of the proposed model is bigger than that of the conventional beam model. Finally, dynamic behaviors of the schematic model under axial impacts are analytically studied.4. A simplified dynamic model is proposed for structures with bolted-flange joints, in which bilinear springs with different stiffness in tension and compression are employed. To validate the proposed model, physical experiments and numerical simulations are performed for a typical bolted flange assembled structure. The physical experiments confirm the existence of the coupling vibration behavior, and the numerical solutions reveal that the proposed model better fits the physical response than conventional beam model.5. Using the proposed simplified dynamic model of bolted flange joint, the linear dynamic beam model of a launch vehicle is modified, through which the joint behaviors are integrated into the dynamic analysis of the whole structure. With the recorded transverse dynamic loads applied on the coupled model, responses of the vehicle are calculated. Axial vibration and force response at the connecting interface are obtained, which meets the test data. This reveals the resource of the axial overload in recorded response data. Static analysis of the connection structure using the extracted internal loads is carried out, which reveals the priority of the coupled model to beam models.