外文原文-利用超声波确定铁素体钢焊缝内部的纵向裂纹的大小.pdf

1、Ultrasonic sizing of embedded vertical cracksin ferritic steel weldsSony Babya,T.Balasubramaniana,R.J.Pardikarb,*aDepartment of Physics,Regional Engineering College,Tiruchirappalli 620015,IndiabNDTL,Bharat Heavy Electricals Limited,Tiruchirappalli 620014,Tamil Nadu,IndiaAbstractEmbedded vertical cra

2、cks are very often encountered in structural components necessitating reliable procedure fordetermining their size.Specialized ultrasonic techniques are required for estimation of through thickness height of thesecracks Mater.Eval.(1970)28;J.NDI 26(1977)320;NND(1975)146.The conventional pulse-echo t

3、echnique hasserious limitations for quantitative estimation of vertical cracks because it is subject to variations due to reflectivity,coupling factors etc.The present study aims to improve the accuracy of embedded crack height measurement based ontransit time rather than the reflected amplitude NDT

4、 Int.(1982)315;J.JSNDT 27(1978)118.A unique method hasbeen developed for generating known sizes of fatigue cracks ranging from 2.5 to 18 mm in height and 15 mm in length.These cracks were generated in rectangular steel specimens and subsequently embedded at predetermined locationsusing welding.These

5、 welded specimens containing the embedded vertical cracks were examined using ultrasonictechniques based on transit time like(a)flaw tip echo method and(b)mode conversion method.Using both thetechniques excellent agreement was obtained between the estimated crack height and actual crack height with

6、an ac-curacy of?1 mm.?2003 Elsevier Ltd.All rights reserved.Keywords:Embedment of cracks;Crack height;Fracture mechanics parameter1.IntroductionWelded structures can fail catastrophically ifthey contain cracks above a certain critical size forthe load applied 6.Using the concepts of fracturemechanic

7、s,it is possible to determine the extentto which a preexisting crack might propagate to anunacceptable level during service.For computa-tion of fracture mechanics parameters like stressintensity factor,it is essential to know the exactlocation,configuration and the size of the cracks.There are many

8、methods for detecting surfacebreaking cracks while only a few techniques pre-vail for detecting embedded cracks 1,35.Recent improvements have been made in theperformance of ultrasonic flaw detectors andtransducers.One of the most promising lines of de-velopment is the use of computers and micropro-c

9、essors along with the digital flaw detectors.Thishas not only reduced the cost of inspection but alsohelped to perform calculations to determine theprojection distances,skip distances,depth of the*Corresponding author.Fax:+91-431-2520710/2520730.E-mail address:rjpbheltry.co.in(R.J.Pardikar).0167-844

10、2/$-see front matter?2003 Elsevier Ltd.All rights reserved.doi:10.1016/S0167-8442(03)00042-9Theoretical and Applied Fracture Mechanics 40(2003) sizes and attenuation co-efficient in aneasy way.The echo height,beam path length,lo-cation and size of the flaw are digitally displayed onthe CRT or LC pan

11、el at real time entirely elimi-nating possibility of human errors.As a resultvarious methods utilizing ultrasonic propagatingtime could be developed for accurate sizing of de-fects.Several techniques have been proposed usingthe bulk waves 2,7,8.However only two suchmethods used for crack height esti

12、mation are out-lined in this paper.2.Specimen preparationThe preparation of the specimen mainly in-volves the generation of fatigue cracks in steelspecimens 9 and welding of the specimens tosubmerge these cracks at predetermined location.The carbon steel blocks of width 90 mm andthickness 16 mm cont

13、aining edge notch of 11 mm(Fig.1)were subjected to fatigue loading usingINSTRON-1276.The fatigue load parameterswere selected such that the operating stress inten-sity factor at the beginning of the fatigue testwould be above threshold stress intensity factorfor the material and that the crack propa

14、gationwould be in the lower part of the stage II regime.The calculations of the stress intensity factor rangeDK can be made fromDK Y Drpa1=21Note that r is stress amplitude,a the crack lengthand Y the compliance factor.Few specimens contain two parallel cracksemanating from starter notches.After rea

15、ching therequired crack length that has grown from thenotch,the specimen were cut to size of 300 mm inlength and machined at the notched edge to re-move the notch and leave behind the crack of re-quired size.The length measurement of the crackwas done using a profile projector.The thicknessof the sp

16、ecimen after machining and the cracklength,were measured precisely before welding,asthese dimensions would give the size of crack thatwould eventually be obtained as submerged crack.The sizes of the edge cracks obtained are shown inTable 1.3.Embedment of crackIn order to get the vertical cracks at the prede-termined locations in the weld for detection andsizing by ultrasonic testing,it was decided to embedthe edge cracks in 32 mm plate approximately atmid-thickness and normal to the test surface