The Impact Detection And Crack Identification Technology Based On The Active And Passive Method Integration

Mechanical and aerospace structures would inevitably suffer from impact in the process of transportation and service,which may result in generation of cracks.Cracks are small and invisible at the initial stage,while with the accumulation of time,they would expand and lead to sudden structural failure,resulting in significant losses.Cracks in structures are harmful and hidden,the research about how to detect fatigue cracks efficiently has always been a hot and difficult issue in structural health monitoring field.Traditional active monitoring methods always have their limitations in practical application.Most of the detection devices are complex,costly,time-consuming,and cannot continuously monitor the structure actively in full-time and real-time.However,passive monitoring methods cannot detect the tiny inherent damage in the structure as well.These shortcomings limit their application in practical engineering.Therefore,a structural health monitoring method based on the active and passive method integration is proposed in this paper.Frequency response function(FRF)is widely used in the field of damage detection because of its convenience,low cost and less error.Active health monitoring technology based on FRF is considered to be one of the most classical and reliable technologies.The traditional damage identification method using linear frequency response function relies on the comparing with the undamaged structure to identify damage,which limits the scope of application of the frequency response function.This paper propose a fatigue crack damage identification method without a reference signature of the undamaged structure based on nonlinear high-frequency response function.Considering the nonlinear nature of damage structure,this paper suggests extract nonlinear components without reference making use of the theory that the forced frequency response function of the cracked beam varies when the beam is excited at two or more amplitudes of excitation by a piezoelectric actuator.Damage index was formed to characterize nonlinear damage.Sensitivity of different frequency bands to detect fatigue crack was also analyzed in this paper.The implemented experiment testifies that this method can effectively identify fatigue cracks without a reference signature.It is difficult to monitor the structural health in full time and real time by using the above methods alone.Combining the passive four-point circular arc impact location method based on the geometric characteristics of sensor array,this paper proposed and studied a structural health monitoring method based on the active and passive method integration.Firstly,the passive method was used to monitor the whole structure in real time and locate the impact instantaneously when the impact occurs.Then,the mentioned active non-reference crack identification method based on frequency response function was applied on the impact location to identify whether the fatigue cracks occur.The simulation experiments on stainless steel plate show that the method can effectively locate the impact position and identify the structural health status.Specific work can be summarized as follows:In the first chapter,the research background of this paper and the research status,background and significance of impact location and damage identification methods based on active-passive combination are introduced.This chapter emphatically introduces the research background of active method based on frequency response function and passive impact location method based on geometric relationship of sensors,while the main work of this paper is introduced in detail as well.In the second chapter,the formation and characteristics of frequency response function are discussed essentially through one-dimensional vibration theory model.The principle of active monitoring method based on the difference of frequency response function under different excitation voltage to identify the non-linear damage of structure is proposed.This chapter also discusses the principle of impact location methods based on piezoelectric materials.In the third chapter,the effectiveness of the non-linear interpolation method is verified by comparing the fatigue crack identification results of cracked beams and intact beams using the non-linear interpolation extraction method.The sensitivity of different sweep frequency bands to the identification of fatigue cracks is also discussed.In the fourth chapter,the passive four-point circular arc impact detection method is validated by the experiment using this method to detect impact of a stainless-steel plate.The active health monitoring method and the passive four-point arc impact location method are combined and proposed as the health monitoring technology based on the active and passive methods Integration.The simulation experiments on stainless steel plate which shows how this method locate the impact position and identify whether fatigue cracks occur is carried out.In the Final chapter,the Summary of the full text is proposed.And this chapter also elaborates the problems and further research directions in this study.