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1、UltrasonicflawdetectionUltrasoundisamechanicalwave,mechanicalvibrationsandfluctuationsinthephysicalbasisofultrasonictesting.Reciprocatingcyclicmovementofanobjectalongastraightlineorcurveinanearequilibriumposition,knownasthemechanicalvibration.Propagat
2、ionofvibration,knownasvolatility.Fluctuationsintomechanicalwavesandelectromagneticwavestwocategories.Mechanicalwavepropagationofmechanicalvibrationsinanelasticmedium.Theultrasoundisamechanicalwave.Themainparametersofthemechanicalwavewavelength,frequen
3、cyandwavevelocity.Wavelengthl:thedistancebetweenthesametwoadjacentoscillationphaseofthesamewavelineparticleknownasthewavelength,sourceormedium,anyoneparticletocompleteafullvibrationwavejustforwardawavelengthdistance,commonlyusedinmeters(m);frequencyf:
4、fluctuationsintheprocess,heservedasagivenpointinonesecond,adoptedbythenumberofcompletewaveiscalledfrequency,commonlyusedinunitsofhertz(Hz);wavevelocityC:fluctuationsinthewaveperunittimetransmittedthedistanceiscalledthewavevelocity,thecommonunitsofmete
5、rs/second(m/s).Wavelengthandwavevelocityisproportionaltoandinverselyproportionaltofrequency;whenthefrequencyisfixed,thewavevelocitythegreaterthewavelengththemorelong;wavevelocitywhenthefrequencylower,themorelongwavelengthavailablebytheabovedefinition:
6、C=l*f.Sub-sonic,sonicandultrasonicmechanicalwavepropagationinanelasticmedium,thepropagationvelocityinthesamemedium.Theirdifferencemainlyduetodifferentfrequencies.Frequencybetween20~20000Hzcancausepeopletohearingthemechanicalwaveiscalledsoundwavesatfre
7、quenciesbelow20Hzmechanicalwavesknownasinfrasonic,frequenciesabove20000Hzofmechanicalwavescalledultrasound.Infrasonic,ultrasoundcannotbeheard.Thefrequencyoftheultrasonicflawdetectionisgenerallybetween0.5~10MHz,theinspectionofsteelandothermetalmaterial
8、s,commonlyusedfrequencyfor1~5MHz.Ultrasonicwavelengthisveryshort,whichdeterminestheultrasoundhasanumberofimportantfeatures,sothatitcanbewidelyusedfornondestructivetesting.Gooddirection:(1)Ultrasoundishighfrequency,veryshortwavelengthmechanical
