Eddy Current- In Brief

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1、ElectromagneticTestingEddyCurrentinBrief2014-DecemberMyASNTLevelIIIPre-ExamPreparatorySelfStudyNotes外围学习中CharlieChong/FionZhangEddycurrenttestingisusedtofindsurfaceandnearsurfacedefectsinconductivematerials.Itisusedbytheaviationindustryfordetectionof

2、defectssuchascracks,corrosiondamage,thicknessverification,andformaterialscharacterizationsuchasmetalsortingandheattreatmentverification.Applicationsrangefromfuselageandstructuralinspection,engines,landinggear,andwheels.Eddycurrentinspectioninvolvesin

3、itialsetupandcalibrationprocedureswithknownreferencestandardsofthesamematerialasthepart.Probesofappropriatedesignandfrequencymustbeused.Eddycurrentinspectionisbasedontheprincipleofelectromagneticinduction.Anelectriccoilinwhichanalternatingcurrentisfl

4、owingisplacedadjacenttothepart.Sincethemethodisbasedoninductionofelectromagneticfields,electricalcontactisnotrequired.CharlieChong/FionZhangFigure1.SchematicofEddyCurrentabsoluteprobeCharlieChong/FionZhangAnalternatingcurrentflowingthroughthecoilprod

5、ucesaprimarymagneticfieldthatinduceseddycurrentsinthepart.Energyisneededtogeneratetheeddycurrents,andthisenergyshowsupasresistancelossesinthecoil.TypicalNDEapplicationaredesignedtomeasuretheseresistancelosses.Eddycurrentsflowwithinclosedloopsinthepar

6、t.Figure2.DiagramillustratingEddyCurrentscreatedinaportCharlieChong/FionZhangAsaresultofeddycurrents,asecondmagneticfieldisgeneratedinthematerial.Themagneticfieldsofthecoreinteractwiththoseinthepartandchangesinthematerialbeinginspectedaffecttheintera

7、ctionofthemagneticfields.Theinteraction,inturn,affectstheelectricalcharacteristicsofthecoil.Resistanceandinductivereactanceadduptothetotalimpedanceofthecoil.Changesintheelectricalimpedanceofthecoilaremeasuredbycommercialeddycurrentinstruments.So,what

8、doesallofthishavetodowithnondestructivetesting?Themainmethodusedineddycurrentinspectionisoneinwhichtheresponseofthesensordependsonconductivityandpermeabilityofthetestmaterialandthefrequencyselected.CharlieChong/FionZhangHoweddycurrentsarecreatedandse