Research On Fatigue Crack Damage Monitoring Technique Based On Wave

Because the structural health monitoring technology based on Lamb wave has merits of full-scale monitoring,wide monitoring,low cost,high sensitivity,low energy consumption,parameterized design.It is payedwide attention to,which worth in depth study and has extensive application prospect.The portal crane is primary handling device in portal work.It is very important to operate safely.Fatigue crack damage is the vital reason why cranes metal structure to lose efficacy,which brings perniciousness to cranes and generally imperils cranes' safe use.The accident caused by fatigue crack damage is disastrous.So,structural health monitoring technology on cranes has vital and profound and lasting meaning.AHE-SGII-1.0fatigue crack monitoring device based on Lamb wave can achieve the function of the real-time,on-line and active surveillance for fatigue crack.The paper has done research on fatigue crack damage monitoring technique based on Lamb wave by fatigue crack monitoring device,which the researching objects are Q235 steel plates used by crane armed metal structure.It lays the foundation of the inspection of cranes' arms.The main works can be generalized as following:(1)Chapter one analyzes the portal cranes' metal structure on which fatigue crack is easy to come to being and perniciousness about the fatigue on cranes.In addition,it says the significance of cranes' metal structure health monitoring based on Lamb wave.Last,it introduces the overseas anddomestic research status about structural health monitoring technology based on Lamb wave.(2)Chapter two introduces the basic theory of Lamb wave which includes the conception of Lamb wave,the propagation mechanism of Lamb wave(for example:dispersion characteristic,many modes,damping)and dispersion curve.(3)Chapter three introduces the basic theory of the piezoelectric component,analyzesthe operating principle of PVDF and PZT,the impactfactors excitation signal and principle that how to elect excitation signal,signal processing technology,the mechanism of monitoring based on Lamb wave and the way of fatigue crack discernment and localization.(4)By finite element methods,the structural health monitoring technique which is applied to one health Q235 steel plate and another damage Q235 steel plate on which fatigue crack is,the Q235 steel plates are applied to cranes' arms.The finite element model was established and CPE4 R was selected in ABAQUS finite element simulation.To ensuring the efficiency and accuracy of the finite element calculation,we chosen 0.2mm as the smallest unite and structured meshing technology.A sinusoidal signal by modulated HANNING window of the center frequency of 100 KHZ and five cycles was selected as excitation signal.The displacement load and free boundary condition was applied to the plate,a time step of 20 ns was setted.Frequency dispersion come up during the process of Lamb wave propagation in the steel plate,at this time,there were two modes of Lamb wave signal,namely a symmetric mode Lamb wave S0 and antisymmetric mode Lamb wave A0.Responsed signal included Lamb wave excitation signal and boundary echo signal in the health steel plate and Responsed signal included Lamb wave excitation signal,and damaged echo signal and boundary echo signal in damaged steel plate.We can identificate and locate the fatigue crack in Q235 steel plate by analyzing the difference responsed signal between healthy plate and damaged steel sheet.The location of fatigue crack is center in steel plate.The effectiveness and feasibility of FEM was verified.(5)In chapter five,experimental research of fatigue crack monitoring technology based on Lamb wave is showed by AHE-SGII-1.0 fatigue crack monitoring device.Piezoelectric ceramic piece acted not only excitation sensors but also sensors during the experiment.Four sensors were arranged in the steel plate,one of sensors acted excitation sensors which excited Lamb waves signal in the plate,the others acted sensors accepting responsed signal.The collected Lamb wave signal was analyzed by wavelet transform.We can get healthy Lamb wave signal,injury Lamb wave signal and the difference signal of the two signal.Fatigue crack-related information was contained in the differential signal.Since Lamb wave in damage come up reflected phenomenon,damaged responed echo signal included defect echo signal,which was able to determine the presence of fatigue cracks.Two ellipses can be determined among three adjacent piezoelectric ceramic sensors,so we can calculate four the lacation of fatigue crack.The fatigue crack on steel plates is discerned and located through signal processing that sensor receives,which lays the foundation of touring inspection.