经典句式英语阅读与写作Ⅳ.docx
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经典句式英语阅读与写作Ⅳ.docx
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经典句式英语阅读与写作Ⅳ
英语阅读与写作Ⅳ课程作业
Classicsentences
姓名:
董素芬
学号:
11406014
学部:
建设工程学部
班级:
02-09周周四3/4节17班
授课教师:
刘文宇
Classicsentences
1—
Interpretationofresultsisbasedonthehypothesisthatelectricalresistivityiscloselyrepresentativeofthevariationinconcretemoisture,withhumiditybeingoneofthemainparametersaffectingcorrosion.
2—
Independentlyoftheriskofcorrosion,resistivitymeasurementsareusedasatooltomaphumidityvariationsinconcretefacings
3—
Thissensitivitycanbeusedtomonitorconcretestructuresusinganintegratedresistivitydevicecastintothestructureitself.
4—
Resistivitysensorsareadaptable,bothintermsoftheinformationthatcanbeobtainedfromthembutalsowithregardtotheiradaptabilitytoconcretestructuresandtheenvironment.
5—
Fromapracticalpointofview,ACISisatechniqueadaptedforlaboratory
study.
6—
Nevertheless,somepracticaldevelopmentsareonthewaytoadaptthispowerfulapproachonsite.
7—
Resistancepertainstotheconductionbehavior,whereasreactancepertains
tothedielectricbehavior.
8—
Thecarbonfiberswereisotropicpitchbased,unsized,andoflength~5mm,diameter15manddensity1.6g/cm3,asobtainedfromAshlandPetroleumCo.(Ashland,Kentucky).
9—
Thispaperconcentratesonconductivecompositeswithconductivefillersandtheiruseforstrainsensingbasedonpiezoresistivity.
10—
Carbonnanotubes(CNT),beingthestrongestknownfiberandpossessingexcellentelectricalproperties,arepromisingcandidatesasthefunctionalfillersforthenextgenerationofpressuresensitivecomposites.
11—
Alltheexperimentswerecarriedoutatroomtemperature.ThemorphologiesofCNTfilledcementmortarcompositeswereexaminedonascanelectronmicroscope(JSM-6490LV,JEOLLtd.,USA).Atleastthreespecimensofeachtypeofcompositesweretested.
12—
ThesefindingsindicatethattheCNTfilledcementmortarcompositeswithSDSand1wt.%ofMWNThaveverypoorpressure-sensitivity.
13—
AcomparisonofFigures1and2indicatesthattheCNTfilledcementmortarcompositeswithSDSand0.2wt.%ofMWNThavebetterpressure-sensitivitythanthosewithSDSand1wt.%ofMWNT,butthepressure-sensitivitiesofboththemareunsatisfactoryforrealapplications.
14—
ExperimentalresultsindicatethatthepiezoresistivesensitivitiesofCNT/cementcompositeswith0.05,0.1,and1wt%ofMWNTfirstincreaseandthendecreasewiththeincreaseofCNTconcentrationlevels
15—
theelectricalresistanceofCNT/cementcompositewith0.6water/cementratioismoresensitivetocompressivestressthanthatofcompositewith0.45water/cementratio.
16—
Piezoresistive(smart)cement-basedcompositesarereinforcedbycarbonfiber(CF)toincreasetheirabilitytosensethestrain,stress,crack,ordamageinthemselveswhilemaintaininggoodmechanicalproperties
17—
thepresenceoftheCFalsocontrolsthecrackingsothatthecracksdonotpropagatecatastrophicallyasconventionalcementbasedmaterial.
18—
BycomparingtheresponsesofelectricalresistanceoftheseCNT/cementcompositestocompressivestress,theeffectsoftheCNTconcentrationlevelandwater/cementratioonthepiezoresistivesensitivityareinvestigated.
19—
Electricalresistanceismeasuredinthecompressivestressdirectionperpendiculartoelectrodesunderrepeatedcompressiveloadingandimpulsiveloading.
20—
Althoughafourelectrodemethodishelpfulforeliminatingthepolarizationeffect,itismorecomplextofixelectrodesandmeasureelectricalresistanceinthefour-electrodemethod.
21—
AscanbeseeninFigure3,theelectricalresistanceRofallthethreetypesofCNT/cementcompositesdecreasesuponloadingandincreasesuponunloadingineverycycleundercompressiveloading,expressingstableandregularpiezoresistiveresponses.
22—
Itisinterestingtonotethatthecomposite’spiezoresistivesensitivitydoesnotlinearlyincreasewithCNTconcentrationlevels.
23—
Twofactorswouldcontributetotheeffectofwater/cementratioonthesensitivityof
piezoresistiveresponse.
24—
Undertheeffectofanappliedpressure,amechanicaldeformationisinduced,andthepolymerthicknessreduces,thusdecreasingthetunnelingbarrier.Asaconsequence,theprobabilityoftunnelingphenomenaincreases,resultinginalargereductionofthebulkelectricalresistance.
25—
Itisthereforeclearthatthelowerthecurvatureradiusoftheconductivetips,thehigherthetunnelingconductanceeffectinthecomposite.
26—
thelowerradiusofcurvatureofthegoldtipshowstoplayhereapredominantroleinthetunnelingconductionenhancement
27—
Inaddition,thankstothesmallcontentofthefillerrequiredanditsnanometricsize,thegoldnanostarscanbeusedtoprepareveryflexible,light,andthincomposites,idealfortheintegrationinMEMS-liketechnologyintactilesensorapplications.
28—
ThedispersionofCNTs/CNFsincementmatrixisevaluatedbyobservingthedispersionofCNTs/CNFsinthesuperplasticizeraqueoussolution,examiningthemorphologyofcomposites,andanalyzingthediscretenessofresistanceofcomposites.
29—
Thecombinationofhighaspectratio,smallsize,lowdensity,anduniquephysicalandchemicalpropertiesmakesthemidealcandidatesasreinforcementsinmultifunctionalcementitiousmaterials
30—
Inaddition,cementitiouscompositescanbeenduedwithpiezoresistivity(i.e.,abilitytosensethestrainorstressinthesecomposites)bytheadditionofCNTs/CNFsincementmatrixes.
31—
theexcessivedopinglevelofNaDDBSorSDShasanegativeeffectonthehydrationofcementandwillcauseadecreaseinthemechanicalpropertiesofcementitiouscomposites.
32—
Inaddition,theforcefuleffectonreducingtheelectricalresistivityofcementitiouscompositesforconductivefillersisduetotheformationofathree-dimensionalconductivenetworkinthecement
33—
theresistanceandresistancediscretenessofthecompositesweretakenasindicatorstoevaluatethedispersionofCNTs/CNFsinthecementmatrix.
34—
ThehighconcentrationandtheeffectivedispersionofCNTs/CNFsarebeneficialforformingthecontactpointsofCNTs/CNFsanddecreasingthetunnelinggapatcontactpointsinthenetwork.
35—
ThemorethecontactpointsbetweentheCNTs/CNFsareandthesmallerthetunnelinggapatcontactpointsis,thehighertheconductivitywillbe.
36—
TheforegoingexperimentalresultsindicatethatcementitiouscompositesfabricatedusingasuperplasticizerasdispersantofCNTs/CNFspresentstableandregularpiezoresistiveresponses.
37—
Thissmartmaterialcanhelpusdevelopintelligentinfrastructureintegratedwithsensingandhealthmonitoringabilities,thusimprovingserviceability,safety,reliabilityanddurabilityoftheinfrastructures.
38—
Itnotonlyhaspotentialinthefieldofstructuralhealthmonitoringandconditionevaluationforconcretestructures,butalsocanbeusedfortrafficdetection,corrosionmonitoringofrebar,militaryandbordersecurity,structuralvibrationcontrolandsoon
39—
Theextremelyhighaspectratio,hollowstructureandlowdensityofCNT/CNFmakeiteasytoformaconductiveandmechanicalreinforcementnetworkinsidematrixwithaCNTconcentrationlevelaslowas0.05wt.%.
40—
Theeffectivedispersionoffunctionalfillers,especiallynano-scalefibersorparticles,isachallengetaskandhasbeenadequatelystudiedandreviewed.
41—
TheirfabricationisakeyprobleminresearchandapplicationoftheISSCsinceelectrodeshavedirectlyrelationwiththeaccuracyofsensingsignalmeasurement.
42—However,someresearcherspointedoutthatalthoughthemeasuredresistancevaluefromthetwo-probemethodmaybehigherthanthetrueresistanceofthecompositesduetotheinfluenceofthecontactresistance,itdoesnotaffectthecapabilityofthetwo-probemethodtodetectchangesinresistanceofthecompositesunderloading
43—
asaDCelectricalfieldisappliedduringtheelectricalresistancemeasurement,themovementandaggregationoftheionsinconcretematrixwillleadtoanelectricalpolarizationinthecomposite,electricalconductionofwhichisdominatedbyionicconductionmechanism
44—
Likerepeatedcompression,thevariationofbaselineelectricalresistivityandthechangeinelectricalresistivityaredifferentunderdifferentamplitudesoftensionstress.
45—
Besidesexternalforces,someotherfactorssuchascompositecomponents,fabricationtechnology,andenvironmentalconditionsalsohaveeffectonelectricalresistivityofthecomposites.
46—
Thereisacriticalcompositionoralsocalledpercolationthreshold,atwhichelectricalconductionisincreasedbyseveralordersofmagnitudeleadingtheISSCfromaninsulatingrangetosemiconductiveandconductiveranges
47—
Severalfactorsmaycontributetothechangeinelectricalresistivity:
(1)Changeofintrinsicresistanceoffunctionalfillers.
(2)Changeofbondingbetweenfunctionalfillersandmatrix.(3)Changeofcontactbetweenfunctionalfillers(4)Changeoftunnelingdistancebetweenfunctionalfillers.(5)Changeofcapacitance.
48—
Generally,thefillerconcentrationabovethepercolationthresholdisbeneficialforthesensingsensitivityundertension,whilethatbelowthepercolationthresholdisbeneficialforthesensingsensitivityunderCompression
49—
Owingtothecapabilityofreflectingitsinsidestress,strain,crackanddamage,theISSChaspotentialapplicationinthefieldsofstructuralhealthmonitoring(SHM)andtrafficdetection.
50—
TheISSCisanintrinsicsmartconstructionmaterialsinceitismadeofconcretematerial,andithasattractedincreasinginterestsoverthelasttwodecades.
52—
Thepiezores
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