Corrosion Diagnosis Methods Of Rod Components Based On Longitudinal Guided Waves

During long-term service,the engineering structure will experience material aging and structural damages.The corrosion of the structural metal framework will lead to deterioration of performance,reduction of bearing capacity and durability,which will influence the safety and reliability of the structures greatly.Corrosive damages have suffered from complex influences,long time span and large uncertainty,etc.Therefore,effective assessment of the corrosive state is significantly important to life-cycle design of the structures.Guided waves attenuates small and travels a longer distance in waveguides,so a large range of coverage can be achieved through only one-time measurement.In recent years,it has gradually become a focus in the field of corrosion monitoring.There are pressing issues in the application of guided waves technology to the corrosion monitoring of engineering components.The significant phenomenon of mode conversion about high-frequency guided waves may cause the complicated scattering signals deriving from corrosive defects,thereby increasing the difficulty of identifying the defect echo signal and destroying the consistency between the amplitude of echo and local corrosion degree.The accuracy and reliability of uniform corrosion evaluated by guided waves will be reduced by the inherent uncertainty of time-frequency analysis and the potential uncertainties during the measurement process.The quantitative relationships between damage indexes and corrosion process are hardly applicable extensively.In this paper,the research objects are specific to the single-layer cylindrical waveguide and embedded cylindrical waveguide.Longitudinal modes of guided waves are used to monitor different types of corrosive damages in a Pitch-catch manner.In view of the above problems,corresponding solutions are proposed to put the current technologies of corrosion monitoring by guided waves forward.The main contents are listed as follows:(1)Take the steel rod as the research object.Through combining multi-mode excitation with time reversal technology,an identification method towards local corrosion is proposed.Experimental and numerical analysis results show that the scattering signals with multi-mode and multi-path from corrosive defect are able to be focused by the method.In the meanwhile,the energy increment of scattering signals with regard to the development of damage can be ensured to be enough.It is verified that the proposed technology is of higher resolution to development of damage and stronger robustness to random features of defect respectively than the traditional defect recognition methods.(2)Take the steel rod as the research object.Considering both the inherent uncertainties of time-frequency analysis and the potential uncertainties involved in the measurement process,a baseline-free method for probabilistic assessment of uniform corrosion is developed based on the dispersion characteristic of guided waves.As for the requirement of both high resolution and precision for the uniform corrosion identification in the current corrosion evaluation process,the Bayesian dynamic linear model is introduced to process the monitoring data and implement the model monitoring.The results show the significantly improved accuracy of the posterior evaluation of corrosive states,and the relevant indicators for model monitoring can presage the starting of the abnormal sequence of guided waves monitoring well.(3)Take the embedded steel bar as the research object.The continuous corrosion monitoring towards reinforced concrete specimens of uniform and local corrosion are carried out by using the guided waves modes of the minimum attenuation.Based on the mechanism of different modes for the corrosion identification and their individual characteristic of energy distribution across the section,the standardized and non-dimensional damage indexes based on the relative amplitudes between the guided waves modes are established.In addition,the velocity sensitivity of the modes with the minimum attenuation to the corrosion of specimens is discussed.The statistical results from the experiment will provide support for subsequent research.(4)Take the embedded steel bar as the research object.Through combining a small amount of observed data with the technology of corrosion monitoring by guided waves using Bayesian strategy,the method which balances accuracy and efficiency is developed for evaluating corrosion quantitatively.The effectiveness and applicability of the method are verified by updating the empirical model based on uniform corrosion samples,which indicates the quantitative relationship between guided wave and corrosion,to a prediction model(posterior information)that meets the accuracy requirement for local corrosion assessment.