外文原文-基于超声TOFD浅埋藏缺陷检测方法.pdf

1、J Nondestruct Eval(2013)32:164171DOI 10.1007/s10921-012-0169-1Shallow Buried Defect Testing Method Based on Ultrasonic TOFDDazhao Chi Tie GangReceived:1 November 2011/Accepted:16 December 2012/Published online:3 January 2013 Springer Science+Business Media New York 2013Abstract Ultrasonic time of fl

2、ight diffraction(TOFD)suf-fers from the shortcoming of lack of near surface resolution,primarily owning to the superposition of the lateral waveand the shallow buried defect(SBD)wave,and the insen-sitive region beneath the inspection surface because of therestricted beam width of the probes.This pap

3、er presentsa method for the detection of SBD based on conventionalTOFD.ThemethodisnamedasTOFDWbecauseitemploysa three-fold reflected longitudinal wave whose propagationpath in the testing piece looks like the letter“W”.Based onPythagorass theory,mathematical models are developed tolocate SBD.In TOFD

4、W mode,the time difference betweenthe lateral wave and the SBD wave can be enlarged greatlyso that they would never be superposed.In addition,throughreflecting the incident longitudinal wave by bottom surface,thenearsurface regionofthetestingpieceiscoveredwithanintenseacousticfield,makingTOFDWfreeof

5、therestrictionof the probes beam width.These contribute to the improve-ment of the near surface resolution.The experiments showthat with the proposed TOFDW and mathematical models,the artificial defect tip with the buried depth of 1 mm canbe detected,and the tips can be measured within an error of0.

6、3 mm;the weld defect with the buried depth of 2 mm canbe identified effectively,and the location can be measuredwithin an error of 0.5 mm.Keywords Time of flight diffraction Shallow burieddefect Defect detection Defect locationD.Chi(?)T.GangState Key Laboratory of Advanced Welding and Joining,Harbin

7、Institute of Technology,Harbin,150001,P.R.Chinae-mail:1 IntroductionUltrasonic time of flight diffraction(TOFD)has provedhighly effective for the inspection of steel plates,tubularpipelines and tanks.The technique has a lot of advantageswhich make it the preferable non-destructive testing(NDT)method

8、 in material testing,especially for the detection andsizing of defects in thick wall weldment.Although TOFDhas started to take its way to replace the other ultrasonictesting techniques,it suffers from several technological lim-itations.TOFDcanbeconductedeasilyfortestingthickwallcom-ponent with simpl

9、e geometry,whereas,complex geometryand thin wall components are difficult to inspect.Througha manual ultrasonic TOFD inspection system,Nath S.K.etal.developed probability of detection(POD)and probabil-ity of sizing(POS)curves for the detection and sizing of sur-face breaking cracksin componentswith

10、complexgeometry.Experiments show that the developed curves are useful forplanning the risk-based inspection of components such as asteam turbine rotor shaft 1,2.However,the scan proce-dures,calibration,data presentation and analysis processesinvolved are often as complex as the geometry itself.Withm

11、iniature high frequency probes and shear wave TOFD,Baskaran G.et al.tried to overcome the limitation of thinsections.In these cases,the minimum thickness that couldbe examined was limited to 7 mm 3.Based on the combi-nation of TOFD and immersion technique,Subbaratnam R.et al.proposed a new method th

12、at extends the application ofTOFD to thinner sections down to 3 mm 4.Although TOFD provides high speed inspection,highsizing reliability and low rate of false defect indications,theidentification and classification of defects is still frequentlyquestioned because it depends heavily on the knowledgea

13、nd experience of the operator.Nowadays,even in state-J Nondestruct Eval(2013)32:164171165of-the-art TOFD scanning systems,the detection and siz-ing of a defect is an almost entirely manual process.In or-der to automatically interpret the data collected by TOFD,pattern recognition techniques,such as

14、artificial neural net-work,are adopted in classification of defect signals 5,6.Digital image processing techniques are studied to automat-ically identify and locate the defects in the images collectedby TOFD.Petcher P.A.and Dixon S.proposed a modifiedHough Transform method,with which the defect can

15、be ex-tractedautomaticallyfromaTOFDB-scanimages7.GangT.and Chi D.Z.presented an approach based on syntheticaperture focusing technique,with which TOFD B-scan im-ages can be enhanced and the defect tips can be located au-tomatically 8.The results obtained from the above studiesare very promising and

16、could give relevant contributions tothe development of an automatic system of classification,detection and localisation of welding defects inspected byTOFD technique.Lack of near surface resolution is by far the most com-monly quoted limitation of TOFD,and it has been substan-tiated by hard fact.An element of the beam in TOFD is de-tected which travels directly from the transmitter to the re-ceiver just beneath the material surface.This is referred toas“lateral wave”,which is a relatively short