The Effect Of Decay On Wood Electrical Resistance

The utilization of wood was low in China while the forest resource could not meet the huge wood demand. So it is necessary to study the wood nondestructive testing and develop new detection method. The Populus davidiana wood was infected by rot fungi in the laboratory to study the impact of wood decay on electrical resistance. The relationship of wood moisture content and electrical resistance was detected, and the equivalent circuit model was built to explain the impact of moisture content on decay wood electrical resistance. The scanning electron microscopy and energy spectrum analysis was used to study the change of microstructure and metal element content in decayed wood. The main research results and conclusions are as follows:(1) The effect of current types on wood resistance was significant, and the DC resistance was higher than the AC resistance. The voltage of DC signals affected the wood resistance which decreased with the increasing voltage. Neither voltage nor waveforms but frequency of AC signals significantly affected the resistance which also decreased with the increasing frequency. So AC signals around 1000 Hz would be more suitable to test the wood resistance as the excitation signal.(2) The electrical resistance of decay wood was significantly different with the sound wood. The electrical resistance decreased rapidly at the beginning and then turned to slow down. The result was coincided with the phenomenon observed on standing tree, which showed that using decay wood infected by fungi in the laboratory to study the change of decay wood electrical resistance was reliable. And the rapid decreased resistance of decay wood indicated that electrical resistance testing method was sensitive in the detection of early wood rot.(3) The electrical resistance of bound water was the key factor affecting the wood electrical resistance. The wood resistance decreased significantly with the moisture increasing below the fiber saturation point (FSP) while the bound water resistance decreased. The relationship of wood resistance and moisture was not significant above the FSP and the wood resistance remained stable with the moisture increasing when the change of bound water resistance was slow.(4) The moisture content of decay wood gradually increased which was significantly higher than the sound wood. Even though the increased moisture content and the decreased electrical resistance occurred at the same time in decay wood, the moisture content was not the main reason which caused the decreasing of electrical resistance.(5) The conduit was destroyed in decay wood where was full of dense mycelium group. The metal element content was significantly increased in the decay wood, especially the potassium ion, which could reduce the electrical resistance. So the increased cation content was the key factor affected the electrical resistance of decay wood.Consequently, the decay wood infected by rot fungi would enrich the cation, such as potassium ion, increasing the ability to transmit electric charge and significantly decreasing the electrical resistance. Moisture content increased in infected wood, but the water played a role as the carrier of charge which could not affect electrical resistance significantly.