Damage Evaluation Of Rail Fatigue Microcrack Via Vibro-Acoustic Modulation

Rail fatigue has properties of long latency,high concealment,and prone to cause sudden brittle fracture.It is one of the most common and dangerous rail flaws,which brings huge safety hazards for the normal track service.Since microcrack is an early sign of rail fatigue,the effective microcrack detection and timely intervention can help permanent way depot strictly control the risk,reduce maintenance costs and solve problems even before they play a role.However,due to the limitation of detection principle,the traditional linear ultrasonic method is not sensitive to rail fatigue microcrack.In this situation,microcracks are always undetectable,which seriously threatens the travelling safety.In contrast,as an advanced nonlinear acoustic detection technology,Vibro-Acoustic Modulation(VAM)method has significant advantages of high detection sensitivity,wide effective detection range,easy to extract the damage signal,etc.It is very suitable for the detection of rail fatigue microcrack,thus eliminating the hidden danger of damaged rail and ensuring high quality railway operation.Therefore,this paper takes rail fatigue microcrack as the research object and proposes a set of damage evaluation algorithm based on VAM technology,thus realizing the identification,quantification,and localization of rail microcrack.It mainly includes the following four parts:(1)extends the nonlinear wave equation under VAM effect.This paper induces an acoustic decay function in exponential form into the VAM nonlinear wave equation,proposes a Compressive Nonlinear Spring(CNS)model based on the correlation between crack opening and closing motion and acoustic transmission,deduces the VAM nonlinear wave equation based on this CNS model,and then designs experiments to verify the above results.(2)proposes a microcrack identification algorithm via time-frequency spectral subtraction method.This paper uses Variational Modal Decomposition(VMD)method to replace Empirical Modal Decomposition(EMD)method in Hilbert-Huang transform for a higher resolution in frequency domain,converts the received signal under excitation with/without low frequency vibration to the time-frequency spectrum,performs subtraction operations and component analysis on them,thus achieving identification and early warning of rail microcrack.(3)proposes a microcrack quantify algorithm via energy-modulation combination method.This paper leverages the quantitative relation of energy loss caused by contact nonlinearity and crack width,combines with the positive relation between the amplitude of the VAM side bound frequency and the nonlinear crack parameter(area s ×the square of width d2),realizes the quantitative assessment of rail microcrack area and width.(4)proposes a microcrack localization algorithm via time-space analysis method.This paper designs a sparse receiver sensor array,proposes a damage center probability matrix calculation method,uses the spatial position distribution of the array elements and the phase difference of damage signals,thus realizing the localization and imaging of rail microcrack by inverse derivation.This paper makes a beneficial exploration for the detection mechanism of vibroacoustic modulation,puts forward a set of "trinity" comprehensive evaluation algorithm covering rail microcrack identification,quantification and localization.Its effectiveness is verified by the rail bottom microcrack detection process.Besides,the method in this paper does not require comparison with the baseline signal of the tested rail under healthy state,does not have to maintain close integration of sensors with rail,will not be affected by interference factors(e.g.,material nonlinearity,boundary reflections,etc.),and effectively improves the utilization of the received signal.Therefore,it is suitable for the detection of rail and other complex structures,thus highlighting the great practical value and broad application potential.The paper includes 53 figures,5 tables and 118 references.