Experimental Study On Damage Detection Of Timber Specimen Based On The Piezoelectric Impedance And Modified Mahalanobis Distance

In recent several decades, Piezoelectric Impedance Technology(PZT) has been extensively employed in structural damage detection and health monitoring, including damage detection of steel structures, reinforced concrete structures, and aluminum structures. However, research related to the application of PZT on damage detection of wooden structure was rarely investigated. Based on previous academic achievements of PZT, the objective of this study focused on investigating the sensitivity of PZT to local damage on wooden structure by means of experimental study. The experimental materials involved Pinus Sylvestris and Bangkirai, which respectively represent the species of conifer and hardwood. The feasibility of application of PZT on wooden structures were explored through measurement and observation of admittance curves before and after damage, which was further studied by introducing Mahalanobis Distance in addition to the traditional indices of Correlation Coefficient(CC)and Root Mean Square error Deviation(RMSD). Since the abnormality in the values of Mahalanobis Distance due to the influence of ill-posed problems, the modified Mahalanobis Distance based on principal component analysis(PCA) was adopted to improve the reliability of the analysis. According to the contents of this thesis, the following conclusions can be drawn:1. PZT was more sensitive to damage on Pinus Sylvestris than Bangkirai. It can be found out that CC and RMSD of Pinus Sylvestris in all frequency ranges could reflect the changes of damage severities, but the counterpart of Bangkirai in several cases did not possess the same regularity.2. The frequency ranges sensitive to damage varied with the damage types. Through the analysis of CC and RMSD, changes in indices of cross grain and rift grain damage were more obvious in the frequency range of 30-50 k Hz, while the counterpart of hole damage were more obvious in the frequency ranges of 30-50 k Hz and 150-500 k Hz.3. Information in multiple frequency ranges were involved in the modified Mahalanobis Distance, which contained more statistical information. Therefore, the difference between various cases were measured from a more comprehensive perspective through this index, thereby a more reasonable evaluation of the application of PZT on wooden structure damage detection could be obtained.In sum, it is feasible and reliable to apply PZT on damage detection of wooden specimens.