The Identification Of Hole And Decay Defect In Wood Disc Based On ERT Propagation Field

There is a large structural contradiction between wood demand and forest resources in our country,because wood utilization rate is low.Wood nondestructive testing study,is one of the important means of improving the wood utilization ratio and it is also for the management and protection of the forest.In theoretical analysis,on the basis of finite element simulation solve.In indoors,two tree species of Populus davidiana as the research object,using the grid test method and the voltage direct measuring method to test respectively electric potential value for disk cross-section of health disk,empty disk,decayed disk.Then,using MATLAB and ArcGIS to draw equipotential graph and current graph,current density.Finally,analyzing equivalent line distribution effected hole defect and decayed defect.By using the method of superposition of the equipotential chart to generate two-dimensional identification figure about cross section of disk defect.Outside,to compare the resistance tomography technology and stress wave detection technology,we get the following conclusions:(1)It is very complex that using the analytic method to solve the electric potential of disk cross-section.However,electrostatic field simulation and steady field simulation can be intuitive show equipotential line distribution in disk cross section.At the same time,the simulation finds that homogeneous medium conductivity does not affect the whole cross section of the equipotential line distribution,the degree of subdivision,load location,and electrode width is significantly influenced on the transverse distribution of equipotential line,compared to a single medium,cross section equipotential line distribution under the two different medium change.(2)On the result of the trial,the frequency has larger influence on measurement results,more than 20 MHZ testing data is not stable,the waveform and voltage has no directly influence on measurement results,test is more convenient and accurate only when a relatively large voltage,and power source type is not too much effect on measurement,a current source is safe and voltage source is more convenient.The selection of zero electric potential reference point has no significant effect on the electric potential distribution,but in order to obtain more stable and more accurate measurements of electric potential,the reference point selection on incentive electrode is the best.Layout spacing has a certain influence on equipotential line,the uniformity of the electric potential distribution in field will more better with the spacing increase.The electric potential distribution in field will more worse with the spacing decrease,it will cause the equipotential line near the incentive electrode is too dense,and in other area special sparse,and will inconvenience observation electric potential.(3)Adjacent incentive mode,equipotential line of the health disk from two electrodes respectively inspires nonlinear diffusion out,in the central axis position to stop,presents a kind of approximate symmetrical distribution.Relative incentive mode,the health of the disk the equipotential line from two incentive electrodes presents corrugated-shape changing,and also stops in the central axis position and presents a kind of approximate symmetrical distribution.(4)Hole can change the whole cross section of the electric potential of high electric potential.The electric potentia increases on one high side of the axis of symmetry,and the electric potentia decreases on one low side of the axis of symmetry.The equipotential line aggregates toward the central axis,near the incentive electrode equipotential line spacing increases,away from the incentive of equipotential line spacing decreases.Electric potential on the central axis has obvious change on the hole disk.Hole diameter is positively associated with equipotential line changing,the hollow position is more significant on the distribution of equipotential line.Decayed also has impact on the same cross section electric potential.The electric potentia increases on one high side of the axis of symmetry,and the electric potentia decreases on one low side of the axis of symmetry.The equipotential line aggregates toward the two incentive electrodes,near the incentive electrode equipotential line spacing decreases,away from the incentive electrode of equipotential line spacing increases,even few equipotential line goes through the electrode.By superpositing the equipotential graph under the different incentives direction,we can roughly describe the position of the hole and decayed defective.(5)A comparison of two detection technologies of ERT and SWT,we find that it is the same affect from hole and decay for the stress wave velocity,yet it is the same affect from hole and decay for resistance.So the ERT on hole and decay identification than SWT technology,but for soft field effect SWT has more advantages on the accuracy of the detection.Combining ERT and SWT,we can preferably identify defect types and estimate the defect area.