Nonlinear vibration characteristics of fiber-reinforced composite thin-walled conical-cylindrical coupled shells under partial bolt looseness

•The conical-cylindrical coupled shells(C-C) were used as the research objects.•The nonlinear characteristics of the C-C under partial bolt looseness were analyzed.•The artificial springs were used to simulate the stick-slip status of bolt joint.•The theoretical model was verified by a series of tests on a self-design testbed.•The import of loose bolt state on nonlinear characters of the C-C were discussed. In the practical engineering application, the bolt connection is commonly used for the assembly of shell structures. High external excitation can lead to partial bolt looseness, further causing interface sticking, sliding or even separation at the connection, resulting in complex nonlinear dynamic problems for bolted shell. Understanding the nonlinear vibration characteristics of fiber-reinforced composite thin-walled conical-cylindrical coupled shells(C-C) under partial bolt looseness is crucial. Therefore, this article investigates the nonlinear vibration mechanism of the C-C under partial bolt looseness. The kinematic equations of conical-cylindrical coupled shells are established by adopting the Lagrange energy equation on the basis of the energy method. The displacement admissible functions of orthogonal polynomials are utilized in combination with the Rayleigh-Ritz method to analyze the vibration characteristics of the C-C. Meanwhile, Jenkins elements are set up at the joint of the substructure shells, and the equivalent stiffness and damping of the bolt connection are obtained by adopting the virtual artificial spring technology to simulate the stick-slip state of the bolt connection, so as to describe the nonlinear behavior of the bolt connection reasonably. The precision of the theoretical model is confirmed by comparing data obtained under different excitations with theoretical calculations using a self-built vibration testing system. Finally, the nonlinear vibration characteristics of the C-C are assessed in terms of different number of bolt looseness, degrees of bolt looseness and forms of bolt looseness. This study provides reference for predicting and evaluating the health state of the bolted shell.