Abstract
Laser ultrasonic technology can provide a non-contact, reliable and efficient inspection of train rails. However, the laser-generated signals measured at the railhead are usually contaminated with a high level of noise and unwanted wave components that complicate the identification of defect echoes in the signal. This study explores the possibility of combining laser ultrasonic technology (LUT) and an enhanced matching pursuit (MP) to achieve a fully non-contact inspection of the rail track. A completely non-contact laser-based inspection system was used to generate and sense Rayleigh waves to detect artificial surface horizontal, surface edge, subsurface horizontal and subsurface vertical defects created at railheads of different dimensions. MP was enhanced by developing two novel dictionaries, which include a finite element method (FEM) simulation dictionary and an experimental dictionary. The enhanced MP was used to analyze the experimentally obtained laser-generated Rayleigh wave signals. The results show that the enhanced MP is highly effective in detecting defects by suppressing noise, and, further, it could also overcome the deficiency in the low repeatability of the laser-generated signals. The comparative analysis of MP with both the FEM simulation and experimental dictionaries shows that the enhanced MP with the FEM simulation dictionary is highly efficient in both noise removal and defect detection from the experimental signals captured by a laser-generated ultrasonic inspection system. The major novelty contributed by this research work is the enhanced MP method with the developments of, first, an FEM simulation dictionary and, second, an experimental dictionary that is especially suited for Rayleigh wave signals. Third, the enhanced MP dictionaries are created to process the Rayleigh wave signals generated by laser excitation and received using a 3D laser scanner. Fourth, we introduce a pioneer application of such laser-generated Rayleigh waves for inspecting surface and subsurface detects occurring in train rails.
Highlights
In the railroad industry, infrastructure safety is its top priority
On the other hand, compared to the original signals, the signal-tonoise ratio (SNR) of the reconstructed signals after matching pursuit (MP) with the finite element method (FEM) simulation dictionary improved significantly, from164.5oft2o0 30.0, 4.8 to 29.1, 7.2 to 30.4 and 4.3 to 31.2 for the surface horizontal defect, surface edge defect, subsurface horizontal defect and subsurface vertical defect, respectively. These results show that MP with the simulation dictionary provides excellent results in terms of rtehme oFvEiMngsnimoiuselaatinodnudniwctiaonntaedrywcaavnebpeaecfkfeectst.ively used for noise suppression and defect detection from a laser-generated Rayleigh wave signal captured at the railhead
TThheerroobbuussttnneessssoofftthheeeennhhaanncceeddMMPPwwitihthFFEEMMsismimuulaltaitoinonanadndexepxepreimrimenetnatladl idctiicotino-anraierisetsotoovoevrecrocmome ethtehelolowwrereppeeaatatabbiliiltiytyoofflalasseerr--ggeenneerraatteeddRRaayylleeiigghhssiiggnnaallsswwaass cchheecckkeedd ffoorrtthheerereccoordrdeeddsisgingnalasls(in(inFiFgiugruer1e51a5–ac)–.cF).irsFti,rMst,PMwPithwtihthe ethxpeeerximpeernimtalendticatliodnicatriyonwaarsy awpapsliaepdptolietdhetsoetmheesaesumreedassuigrendalssi.gTnhaelsr.eTcohnesrtercuocntesdtrsuicgtneadlssiagfntearlsMaPftaerreMshPoawren sinhoFwignurine Figure 16a,c,e for day 1, day 2 and day 3, respectively. These results show that MP with the experimental dictionary successfully extracts the incident waves and defect echoes, the measured signals had different noise levels and unwanted wave packets
Summary
Infrastructure safety is its top priority. maintenance of the rail track structure has been one of the most significant challenges since railroading began. Several research groups have investigated LUT for the inspection of rail tracks [9,10,11,12,13,14,15] In these works, for the non-contact detection of laser-generated ultrasonic waves, mostly EMAT [9] and air-coupled transducers [11,12] were used. This research’s major novelty is the enhancement of matching pursuit by developing an experimental dictionary consisting of laser-generated Rayleigh wave signals recoded at railheads. An utterly non-contact laser-based inspection system was used for railhead defect detection and to design the experimental dictionary. The functioning of the enhanced MP with experimental and FEM simulation dictionaries was tested successfully on laser-generated Rayleigh wave signals recorded at railheads of different dimensions having different types of surface and subsurface defects.
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