Study On Acoustic Emission Monitoring Method Of Longitudinal And Transverse Localization Of Defects And Wire Breaking In Parallel Wire Bundle

As the main structure of cable bridge,cable system will inevitably reduce the safety,applicability and durability of cable bridge once it is damaged under vehicle load and complex natural environment.Therefore,the monitoring of the damage and wire breaking of the bridge cable and the precise positioning of the longitudinal and transverse direction play a vital role in the safe operation of the bridge.In view of this,the main research work in this paper is as follows:(1)The transition mode of the waveguide and the sensor and the connection mode of the waveguide and the cone platform are compared and studied.The transition mode and connection mode are the key links in the precise monitoring of acoustic emission,which directly determines the correctness and accuracy of the monitoring results.Through precise monitoring,the optimal transition mode of the waveguide and the sensor and the connection mode of the waveguide and the cone platform connection can be determined.The method of lead break test is used in this study.Then,the effects of three transition modes(cone platform,line,and surface transitions)between the waveguides and sensors on the acoustic emission signals are investigated.Furthermore,the effects of four connection modes(welding,threaded,adhesive,and magnetic connections)between the waveguides and cone platform on the acoustic emission signals are studied.Waveform and parametric analyses are conducted,and the acoustic emission signals of the different modes(three transitions and four connections)and that of the reference sensor are compared to find the optimal transition and connection modes mentioned above.The results are as follows.Waveform and parameter analytical results show the following: the cone platform transition is superior to the surface transition and line transition;the welding connection is superior to the threaded connection,adhesive connection,and magnetic connection;the sensor–wave guide rod is better than the cone transition surface transition and transition line;and the welded waveguide rod and cone is better than the thread connection,adhesive bonding,and magnetic connection.Therefore,when using waveguides to monitor structures,the cone platform transition should be selected for the sensor and waveguide,whereas the welding connection mode should be selected for the waveguide and cone platform.(2)Acoustic emission monitoring is conducted to accurately identify the wire breaking of the cross-section cable by using the waveguide technique.The prime focus is to conduct a safety assessment of the bridge to determine the affected wires in the wire-breaking part of the cable.Accordingly,this study forwards an innovative monitoring method of using waveguides to identify the steel wire at the end of the cable and directly collect acoustic emission signals generated by its internal steel structure.The monitoring method effectively captured the acoustic emission signals generated by the damage and wire breaking of the cable.The transverse position of the cable damage and wire breaking are also located accurately.The findings can therefore provide the basis for decision-making of the maintenance department.In this study,the methods of the lead breaking and tensile tests are used to investigate the cross-section location of the damage and wire breaking of the parallel wire bundle.The tensile and lead breaking tests both show that the transverse position of the steel wire that produced the damage and wire breaking can be located transversely by analyzing the characteristics of the acoustic emission signals received by the sensor at the end of the cable.Both tests exhibit high reliability and accuracy.(3)Acoustic emission monitoring is adopted to accurately identify the longitudinal damage and wire breaking of the cable by referring to a single sensor.The method of traditional vertical positioning requires two sensors to be fixed at both ends of the wire,but this setup is extremely inconvenient when applied to engineering structures.Similarly,constant sound speed can cause large errors in the longitudinal positioning.To find a precise and convenient method for the longitudinal positioning of steel wire breaking,the longitudinal location of the wire breakage based on the cross-section location of the parallel wire bundle is investigated.First,the dispersion equation of circular bar-guided waves is derived in accordance with the theory of modal acoustic emission,the related parameters of the steel wire are inputted into the compiled Matlab program,and the group velocity curves of the different modes of the high-strength steel wire are calculated.Then,the longitudinal location of the single sensor corresponding to the damage and wire breaking is determined by using the related feature points in the time-frequency graph of the continuous wavelet transform.The results show that the positioning method can be improved in terms of accuracy in multimode conditions.Furthermore,the positioning method can enhance the frequency dispersion characteristics,which initially cannot be used to accurately locate the damaged wire source.The longitudinal positioning method,which is based on the dispersion characteristics of the wire-guided waves,for the single sensor has high accuracy and reliability.Using a single sensor is feasible when locating the longitudinal position of the damage and wire breaking of a steel wire.