简介:TheeffectoffrequencyandsampleshapeonfatiguebehaviorsofDZ125superalloyaresystematicallystudied.Theresultsshowthatfatiguefracturestilloccursabovethecycleof10~8fortestscarriedoutatthefrequencyoff=20kHzandstressratioR=-1,sothetraditionalfatiguelimitatcycleof10~7isnotappropriateforfatiguedesign.Fatiguefracturesurfacesareperpendiculartostressaxisforcylindricalandplatespecimens,andthefatiguecracksoriginatefromtheextrasurfaceofthespecimens.Fatiguecrackisapttopropagatefromcuttingdirectiontoforwarddirection,whichoccursmainlyinthesecondpropagationstageathigherstressamplitude.ThereisanobviousfrequencyeffectforDZ125superalloy.Thehigherthetestfrequencyis,themoreserioustheeffectoffrequencyonfatiguebehaviorsofthealloy.Afterthefrequencycorrection,theultra-highcyclefatigueS-NcurvewellcoincidewiththetraditionalfatigueS-Ncurve.
简介:Shortpeptidesbasedonthetripeptides,Leu-Arg-ProandLeu-Lys-Pro,weresynthesizedbymicrowaveassistedsolid-phasesynthesismethod,inordertomakeasearchforpotentialinhibitorsforangiotensinI-convertingenzyme(ACE)withminimumsideeffectsinthetreatmentofhypertension.OnepeptidewiththesequenceLeu-Arg-Pro-Phe-PheshowsthestrongestinhibitiontowardsACEwithanIC50valueof0.26μmol/Linvitro.Thestudyofstructure-activityrelationshipshowsthattheintroductionofabulkygroupintotheN-terminalofthisseriesofinhibitorsmayenlargesterichindrance,resultinginthepoorinhibitoryactivitytowardsACE.TheinhibitoryactivitydecreasedinturnwhenL-Pro,D-ProorAc6cwasattheC-terminalrespectively.ThebindinginteractionbetweeneachoftheseinhibitorsandtesticularACE(tACE)wasperformedbymoleculardocking.TheresultssuggestthatLeu-Arg-Pro-Phe-PhemainlyoccupiedtheS1subsiteoftACE,andmadecontactwithtACEviasevenH-bonds.ItappearedthatthesiteonthepeptidethatboundwithtACEwasinfluencedbytheconfigurationoftheaminoacid,LorD-form,attheC-terminalofthepeptide.