Evaluating bolt connecting faults in ring-type structures with nonlinear fault-induced loads and transmissibility functions

•Nonlinear dynamics of local substructures of complex ring-type structures with nonlinear connecting components are studied.•Novel and local fault evaluation features are proposed, based on nonlinear fault-induced loads and transmissibility functions.•Novel, sensitive and reliable local indexes are established for complex ring-type structures.•The method fully considers nonlinear boundaries, simply works with only three-time harmonic excitations, and needs no reference models at all.•This method is very easy to implement and applicable to many other connecting faults in plate-type and rotor-like structures. Existing vibration-based methods often encounter some obvious limitations when they are applied to evaluate bolt connecting faults in ring-type structures, e.g., steel truss bridges in civil engineering and copper interlaced pipes in aerospace engineering. To overcome these limitations like ignorance of structural nonlinear boundaries, consideration of entire structural dynamics, and requirement of benchmark vibration data etc., a novel fault evaluation method is thus proposed. To this aim, the dynamic behaviour of ring-type structures is described by a discrete ring-type multiple degree-of-freedom (MDOF) model with nonlinear connecting components simulating bolt connecting faults and structural nonlinear boundaries. By exciting the ring-type structure three times with appropriate amplitudes of harmonic excitations, stationary vibration data are collected and evaluation features based on nonlinear fault-induced loads and transmissibility functions are defined. Finally, an effective evaluation method with sensitive and local indexes is established for complex ring-type structures. The method works with only three-time excitations for measured output data, and it is easy to implement to many other similar structures with complex, coupling and inter-connected nonlinearities. Experimental results with comparison to other two general nonlinear transmissibility function-based methods vindicate that the proposed method is more reliable and sensitive, demonstrating a totally new approach to such a challenging issue in engineering practices.