Research On Self-loosening Mechanism Of Three Coatings Bolted Joints Under Tangential Excitation

Bolted joint structure is widely used in mechanical fastening or mechanical power structure because of its excellent characteristics such as high reliability,simple structure and convenient disassembly.However,due to the influence of surrounding difference in temperature,vibration,impact,fatigue load and corrosion atmosphere,it is easy to lead to loosening,wear,bending deformation and even fracture.Bolted joint structure plays a key role along with its complex loosening behavior,which attracts domestic and foreign scholars to carry out in-depth theoretical and experimental research,but currently the focus of attention is mainly on the variety of excitation forms and eccentricity distance.However,there is little research on the angle of bolt contact interface.In this paper,the loosening mechanism of coated bolt connection under tangential loading is emphatically tested,and to reach the loosening and wear mechanism.Meanwhile,the practical engineering analysis of fretting tribology in fastener bolt field has carried out while enriching the loosening theory of bolting structure.Application,expansion and other fields have major guiding significance.Based on the self-developed multi-channel data acquisition system and surface engineering technology.this paper studies the loosening behavior of three kinds of coating bolted structures under tangential excitation:by means of pre-tightening force,vibration amplitude,tightening torque,the equivalent stress and other parameters were set,the loosening curve was collected and analyzed,and the loosening mechanism of different coating bolted connection structures was studied.The wear mechanism has revealed by further analysis of the micro-morphology and composition of the working thread.Further,the loosening degree and wear degree of three kinds of coating bolted connections has analyzed and compared,and the applicability of different coated bolted connection structures are obtained,which provides a technical reference solution for solving the loosening problem of bolted connections in some key fields.The main conclusions of this paper are as follows:?1?The loosening of coated bolted joints under tangential load has divided into three different stages.In the first stage,the axial force decreases rapidly in the initial grinding-in category;In the second stage,the axial force decreases slowly,mainly due to the stable loading of the equipment and the plastic deformation of the bolt structure,as well as the removal of the rough peak on the surface of the thread contact coating with the test.The third stage:the residual axial force of bolt decreases more slowly until stable.Fretting wear occurs between the ratchet effect of material and the coating of contact interface,and the condition of friction pair among contact interface is improved by the coating exfoliated.The residual axial force of the bolt finally tends to be stable.?2?The research on blue-white zine coating bolt shows that with the increase of pre-tightening force,the loosening degree and the wear degree of working thread decreases.The loosening condition and wear degree gradually aggravate with the increase of vibration amplitude,and the wear mechanism mainly includes abrasive wear,fatigue wear and oxidation wear via the analysis of the morphology and composition of contact thread micro-zone.?3?The connection structure of the coated WC/C coating and the MoS₂ coating bolt is tested to show that the preload force on the bolt connection of the MoS₂ coating has a significant effect,and the too small preload force can lead to the rapid loosening of the MoS₂coating bolt.Under the action of the appropriate preload force,the looseness of the two coating bolts is equivalent,Further morphology analysis show that the WC/C coating has better wear resistance than the MoS₂ coating,and the wear mechanism of the two coating bolts mainly includes abrasive wear and fatigue wear.