State Detection For Bolted Joints Based On Frequency Tracking Method

In machinery,transportation,electric power,aviation,civil and other industries,bolted joints are widely used between parts and components in the equipment,bolted connection's reliability is directly related to the whole structural reliability and safety of the equipment.The state of bolted connection is related to the contact characteristics of the bolted joints interface,therefore,research on the contact characteristics of the bolted joints interface and effective monitoring of the bolted connection state are useful to avoid bolt failure.The state monitoring method based on frequency tracking method is used to study the contact characteristics of the bolted connection state and the contact surface in the thesis.The main contents are following:(1)According to Hertz contact theory,constructing the micro-model of the bolted joint interface,the relationship between normal contact stiffness and pre-tightening force is derived to be monotonic function;the relationship between the normal contact stiffness and the modal frequency of the bolted connection structure is two terms of the function relation,so do the relationship between the model frequency and pre-tightening force.(2)The surface topography of the samples are measured by a profiler;the real profile curve of rough surface is imported to finite element;the finite element of the contact between rough surface and rigid surface is established to be analyzed.Results show :the relationship between the normal contact stiffness and pre-tightening force is monotonically increasing;the roughness of interface has influence on normal stiffness,the less the roughness the bigger the normal stiffness.A symmetry model of bolted joint is established for finite element simulation of frequency tracking method.Resultsshow: the relationship between model frequency of bolted joint and pre-tightening force is two terms of function relation.(3)The experimental scheme of bolted joint state monitoring method based on frequency tracking is designed;the experimental system is established to be studied.Resultsshow: the less the roughness,the bigger the normal stiffness;the relationship between model frequency of bolted joint and pre-tightening force is two terms of function relation which verified the correctness of the theoretical analysis and finite element simulation and a monitoring method of bolted joint state based on frequency tracking is proposed.