Damage Monitoring Of Wooden Structure Based On Piezoelectric Sensing Technology

In recent years,piezoelectric transducers and their technologies have the advantages of low cost,fast response and strong piezoelectric effect,and have made great progress in the health monitoring and damage assessment of various metal,concrete structures and loose bolts.Timber is a kind of an environmentally friendly,easily available and easily processed structural material,will be the domestic mainstream for a period of time in the future,and the the cost and technical threshold is relatively low,inside and outside modelling diversity,with light deadweight,easy transportation and installation,is often used in building construction.Timber structures often will be subjected to loads or complex disasters,which may cause damage of interior and surface in the actual use process.If such damage cannot be detected in time and allowed to expand,it will endanger the service life of wood structures,however,there is still a lack of research on damage monitoring of timber structures based on piezoelectric sensing technology.In this paper,based on the active monitoring technology of piezoelectric ceramic sensors,damage detection of timber structures were studied.The main research contents are as follows:(1)This paper introduces the principle of structural health monitoring based on piezoelectric ceramic.The positive and negative piezoelectric effect of piezoelectric ceramics is introduced.Piezoelectric ceramics can be used as the drive,also can be used as a sensor.This paper introduces the detection system of wave method and piezoelectric impedance technology,describes the research background of wave method and piezoelectric impedance technology,the research process and theoretical analysis of many domestic and foreign scholars,and discusses the future development direction of piezoelectric sensors.(2)Based on the active monitoring technology of piezoelectric ceramics,the wave method is used to study the feasibility of real-time damage monitoring of timber short columns under compression load.A pair of piezoelectric ceramic plates were pasted on opposite sides of the radial side of the timber short columns respectively.One ceramic plate was used as the driver,and the ceramic plate was stimulated to generate directional stress wave through the waveform transmitter,while the other piezoelectric ceramic plate was used as the sensor to receive the transmitted stress wave signal.Timber short column specimen under load from health to completely destroy the whole loading process,the materials properties of timber with loads of different shows that timber internal damage accordingly,stress wave signal is affected by the flaws,the stress wave energy is reduced,through the change of the stress waveenergy to reflect the reality of structure damage process.The results show that there is a positive correlation between the load action and the stress wave energy of the timber short column,and the damage index is proposed to reflect the damage development of the structure.The feasibility and reliability of this method for damage monitoring of timber short columns under compression load are discussed.(3)In this paper,based on the active monitoring technology of piezoelectric ceramics,the wave method is used to study the feasibility of monitoring tenon and mortise joint damage of timber structure.A pair of piezoelectric ceramic plates were used to paste on the surface of the tenon and mortise of timber structure.In the wave method,a ceramic chip acts as a driver and is excited by a waveform transmitter to generate a directional stress wave,while another piezoelectric chip acts as a sensor to receive the transmitted stress wave signal.With the increase of the loosen degree of timber,the stress wave signal is affected by the timber loosening,resulting in the rapid attenuation of the stress wave energy.The results show that the time-frequency response signal graph can directly reflect the relation between the loosen length of timber and the signal amplitude.The damage index(RMSD)was proposed to evaluate the loosen degree of timber structure joints,so as to verify the feasibility of monitoring the looseness of timber mortise and tenon joints in real time.(4)Based on the piezoelectric impedance technology in the active monitoring method of piezoelectric ceramics,the electromechanical coupling effect of piezoelectric sensors is used to monitor the moisture content of timber.This paper adopts a lead zirconate titanate(PZT)sensor paste on the surface of timber,and applying frequency excitation signal local shock wave to drive some vibration timber,as the change of moisture content of timber,the structure strength and stiffness to change itself,the corresponding mechanical impedance will change,through the coupling of electrical impedance,through the analysis of the relationship between the impedance parameters and moisture content,and estimation size of moisture content of timber.The results show that there is a positive correlation between impedance real part and moisture content of timber.The relationship between damage index(RMSD)and moisture content of timber was obtained by using mathematical statistical method.In summary,the active monitoring technology based on piezoelectric ceramics is applied to the damage monitoring of timber structures.From the principle to the experimental design,the experimental results prove that the method can effectively monitor the damage of timber structure.