Research On The Self-Loosening Behavior Of Three Kinds Of Threaded Connection Structures Under Shear Excitation

The threaded connection structure has the advantages of connection and fastening,besides its structure is simple and easy to disassemble and low cost,so it is widely used in various engineering structures.It plays a key role in many aspects,such as in connecting and fastening,transmitting force(or torque)together with ensuring structural sealability.In engineering practice,the threaded connection is often subjected to these types of external loads,especially the vibration conditions of working.In the vibration environment,the thread connection is prone to loose,which seriously affect the safe operation of various structural parts,and even cause major safety accident.At present,scholars at home and abroad have extensively studied the structure of the thread connection,but most of them have focused on the ordinary structure without the anti-loosening measures,only some researches on the anti-loose thread structure is not deep and enough,so it is necessary to carry out research on some threaded connections with specific locking structures.Because this not only can deepen and broaden the understanding of the loosening mechanism of the thread connection,but also can provide important theoretical guidance for the practical application of various anti-loose structures.In this paper,the loosening mechanism and the anti-loosening performance of the anti-loose thread connection structure are studied.The main contents and the main conclusions are as follows:(1)Based on the analysis of the dynamic response of the threaded connection structure and the damage morphology of the thread surface,it is found that the loosening process of the thread connection can be two stages.The loosening mechanism of the first stage is mainly due to the plastic deformation of the structure.The loosening mechanism of the second stage is mainly fretting Wear of Thread Contact Interface.(2)A loosening test device for the screw-connected structure under the transverse excitation and a measuring device for the rotation angle of the nut relative to the screw are developed,and the loosening process of the bolt connection structure under the transverse excitation is reproduced by the test.(3)According to the different test parameters(load amplitude and preload),the loosening behavior of the screw connection structure is studied by the macroscopic test and the microscopic test.It is revealed that the bolt/nylon insert loose mechanism of nut connection structure.The results showed that the degree of looseness of the thread is inversely proportional to the size of the preload,which is proportional to the magnitude of the transverse alternating load.Also,the degree of damage to the crest of the thread is more serious.With the increase of the number of threads,the degree of damage to the thread surface will lower.However,due to the precision of machining and the difference of surface roughness,the test results are dispersive and do not strictly follow this law.What's more,the main wear mechanism of the thread contact interface is adhesive wear,abrasive wear,fatigue wear and oxidation wear.(4)According to the same test parameters(load amplitude and preload),the screw connection structure was studied by means of macroscopic test and micro-test method.The results showed that the connection structure loosening behavior of the bolts/nylon inserted nut,ordinary nuts and tapered tightening nuts is revealed.The search shows that under the same conditions:the three kinds of nuts with different structural are arranged in order the anti-loose performance from the high to the low,which the highest is the tapered tightening nuts,nylon inserted nut are better,and ordinary nuts are the worst.