ECSS-E-ST-32-10C_Rev.1(6March2009).pdf

ECSS-E-ST-32-10C Rev.1 6 March 2009

Space engineering Structural factors of safety for spaceflight hardware

ECSS Secretariat ESA-ESTEC

Requirements & Standards Division Noordwijk, The Netherlands

ECSSEST3210CRev.16March2009

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Foreword

This Standard is one of the series of ECSS Standards intended to be applied together for themanagement, engineering and product assurance in space projects and applications. ECSS is acooperative effort of the European SpaceAgency, national space agencies and European industryassociationsforthepurposeofdevelopingandmaintainingcommonstandards.RequirementsinthisStandardaredefinedintermsofwhatshallbeaccomplished,ratherthanintermsofhowtoorganizeandperform thenecessarywork.Thisallows existingorganizational structures andmethods tobeappliedwheretheyareeffective,andforthestructuresandmethodstoevolveasnecessarywithoutrewritingthestandards.

ThisStandardhasbeenpreparedby theECSSEST3210CWorkingGroup, reviewedby theECSSExecutiveSecretariatandapprovedbytheECSSTechnicalAuthority.

Disclaimer

ECSSdoesnotprovideanywarrantywhatsoever,whetherexpressed,implied,orstatutory,including,butnotlimitedto,anywarrantyofmerchantabilityorfitnessforaparticularpurposeoranywarrantythat the contents of the item are errorfree. In no respect shall ECSS incur any liability for anydamages,including,butnotlimitedto,direct,indirect,special,orconsequentialdamagesarisingoutof,resulting from,or inanywayconnected to theuseof thisStandard,whetherornotbaseduponwarranty,businessagreement,tort,orotherwise;whetherornotinjurywassustainedbypersonsorpropertyorotherwise;andwhetherornotlosswassustainedfrom,oraroseoutof,theresultsof,theitem,oranyservicesthatmaybeprovidedbyECSS.

Publishedby: ESARequirementsandStandardsDivision ESTEC, P.O. Box 299, 2200 AG Noordwijk The Netherlands Copyright: 2009 by the European Space Agency for the members of ECSS


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Change log

ECSSEST3210A Neverissued

ECSSEST3210B Neverissued

ECSSEST3210C

31July2008

Firstissue

ECSSEST3210CRev.1

6March2009

Firstissuerevision1

ChangeswithrespecttoversionC(31July2008)areidentifiedwithrevisiontracking.

Mainchangesare:

ChangeofdocumenttitlefromReliabilitybasedmechanicalfactorsofsafetytoStructuralfactorsofsafetyforspaceflighthardware

AdditionofatypicalvalueforKMassociatedtointernalpressureforpressurizedhardwareinclause4.1.4.2b

AdditionofrequirementsforFOSforthermalinducedloadsinclause4.3.2.1

CorrectionofTable42:Testfactorvalues Editorialcorrections


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Table of contents

Change log .................................................................................................................3

1 Scope.......................................................................................................................6

2 Normative references.............................................................................................8

3 Terms, definitions and abbreviated terms............................................................9 3.1 Terms and definitions .................................................................................................9 3.2 Terms specific to the present standard ......................................................................9 3.3 Abbreviated terms ....................................................................................................10

4 Requirements........................................................................................................11 4.1 Applicability of structural factors of safety ................................................................11

4.1.1 Overview.....................................................................................................11 4.1.2 Applicability.................................................................................................11 4.1.3 General.......................................................................................................11 4.1.4 Design factor for loads................................................................................11 4.1.5 Additional factors for design .......................................................................13

4.2 Loads and factors relationship .................................................................................14 4.2.1 General.......................................................................................................14 4.2.2 Specific requirements for launch vehicles ..................................................16

4.3 Factors values ..........................................................................................................17 4.3.1 Test factors.................................................................................................17 4.3.2 Factors of safety .........................................................................................18

Annex A (informative) Qualification test factor for launch vehicles ...................22

Bibliography.............................................................................................................24 Figures Figure 4-1: Logic for Factors of Safety application.................................................................15 Figure 4-2: Analysis tree ........................................................................................................16


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Tables Table 4-1: Relationship among (structural) factors of safety, design factors and

additional factors..................................................................................................15 Table 4-2: Test factor values..................................................................................................17 Table 4-3: Factors of safety for metallic, FRP, sandwich, glass and ceramic structural

parts.....................................................................................................................19 Table 4-4: Factors of safety for joints, inserts and connections .............................................20 Table 4-5: Factors of safety for buckling ................................................................................21 Table 4-6: Factors of safety for pressurized hardware...........................................................21


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1 Scope

Thepurposeof thisStandard is todefine theFactorsOfSafety (FOS),DesignFactor and additional factors to be used for the dimensioning and designverification of spaceflight hardware including qualification and acceptancetests.

ThisstandardisnotselfstandingandisusedinconjunctionwiththeECSSEST32,ECSSEST3202andECSSEST3301documents.

Followingassumptionsaremadeinthedocument:

thatrecognizedmethodologiesareusedforthedeterminationofthelimitloads,includingtheirscatter,thatareappliedtothehardwareandforthestressanalyses;

that the structural and mechanical system design is amenable toengineering analyses by current stateoftheart methods and isconformingtostandardaerospaceindustrypractices.

Factorsof safety aredefined to cover chosen load levelprobability, assumeduncertainty in mechanical properties and manufacturing but not a lack ofengineeringeffort.

Thechoiceofafactorofsafetyforaprogramisdirectlylinkedtotherationaleretained for designing, dimensioning and testing within the program.Therefore,asthedevelopmentlogicandtheassociatedreliabilityobjectivesaredifferentfor:

unmannedscientificorcommercialsatellite, expendablelaunchvehicles, manratedspacecraft,and anyotherunmannedspacevehicle(e.g.transfervehicle,planetaryprobe)specificvaluesarepresentedforeachofthem.Factors of safety for reusable launch vehicles and manrated commercialspacecraftarenotaddressedinthisdocument.

For all of these spaceproducts, factors of safety aredefined hereafter in thedocumentwhatever the adopted qualification logic:protoflightorprototypemodel.

Forpressurizedhardware,factorsofsafetyforallloadsexceptinternalpressureloadsaredefinedinthisstandard.Concerningtheinternalpressure,thefactors


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ofsafetyforpressurisedhardwarecanbefoundinECSSEST3202.ForloadscombinationrefertoECSSEST3202.

Formechanisms,specificfactorsofsafetyassociatedwithyieldandultimateofmetallicmaterials,cable rupture factorsof safety, stops/shaft shoulders/recessyieldfactorsofsafetyandlimitsforpeakHertziancontactstressarespecifiedinECSSEST3301.

Alternateapproach

The factors of safety specified hereafter are applied using a deterministicapproach i.e. as generally applied in the Space Industry to achieve thestructures standard reliability objectives. Structural safety based on aprobabilistic analysis could be an alternate approach but it has to bedemonstrated this process achieves the reliability objective specified to thestructure.Theprocedureisapprovedbythecustomer.

ThisstandardmaybetailoredforthespecificcharacteristicsandconstraintsofaspaceprojectinconformancewithECSSSST00.


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2 Normative references

The following normative documents contain provisions which, throughreference in this text, constitute provisions of thisECSS Standard. Fordatedreferences,subsequentamendmentsto,orrevisionofanyofthesepublications,donotapply.However,partiestoagreementsbasedonthisECSSStandardareencouragedtoinvestigatethepossibilityofapplyingthemorerecenteditionsofthenormativedocuments indicated below. Forundated references, the latesteditionofthepublicationreferredtoapplies.

ECSSSST0001 ECSSsystemGlossaryofterms

ECSSEST1002 SpaceengineeringVerification

ECSSEST1003 SpaceengineeringTesting

ECSSEST32 SpaceengineeringStructuralgeneralrequirements

ECSSEST3202 SpaceengineeringStructuraldesignandverificationofpressurizedhardware


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3 Terms, definitions and abbreviated terms

3.1 Terms and definitions ForthepurposeofthisStandard,thetermsanddefinitionsfromECSSSST0001,ECSSEST1002,ECSSSTE1003,andECSSEST32apply.

3.2 Terms specific to the present standard 3.2.1 local design factor (KLD) factorusedtotakeintoaccountlocaldiscontinuitiesandappliedinserieswithFOSUorFOSY

3.2.2 margin policy factor (KMP) factor,specifictolaunchvehicles,whichincludesthemarginpolicydefinedbytheproject

3.2.3 model factor (KM) factorwhichtakesintoaccounttherepresentativityofmathematicalmodels

3.2.4 project factor (KP) factorwhichtakes intoaccountatthebeginningoftheprojectthematurityofthedesignand itspossibleevolutionandprogrammaticmarginswhichcoverprojectuncertaintiesorsomegrowthpotentialwhenrequired

3.2.5 prototype test testperformedonaseparateflightlikestructuraltestarticle

3.2.6 protoflight test testperformedonaflighthardware

3.2.7 test factors (KA and KQ) factors used to define respectively the acceptance and the qualification testloads

3.2.8 ultimate design factor of safety (FOSU) multiplying factor applied to the design limit load in order to calculate thedesignultimateload


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3.2.9 yield design factor of safety (FOSY) multiplying factor applied to the design limit load in order to calculate thedesignyieldload

3.3 Abbreviated terms For thepurposeof thisstandard, theabbreviated terms fromECSSSST0001andthefollowingapply.

Abbreviation MeaningAL acceptancetestload

DLL designlimitload

DUL designultimateload

DYL designyieldload

FOS factorofsafety

FOSU ultimatedesignfactorofsafety

FOSY yielddesignfactorofsafety

FRP fibrereinforcedplastics

GSE groundsupportequipment

KA acceptancetestfactor

KQ qualificationtestfactor

LCDA launchvehiclecoupleddynamicanalysis

LL limitload

N/A notapplicable

QL qualificationtestload

S/C spacecraft


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4 Requirements

4.1 Applicability of structural factors of safety

4.1.1 Overview ThepurposeofthefactorsofsafetydefinedinthisStandardistoguaranteeanadequatelevelofmechanicalreliabilityforspaceflighthardware.

4.1.2 Applicability a. Thefactorsspecifiedinclauses4.1.4,4.1.5and4.3shallbeappliedfor:

1. Structural elements of satellites including payloads, equipmentandexperiments.

NOTE ThesefactorsarenotappliedfortheGSEsizingandqualification.

2. Theexpendablelaunchvehiclesstructuralelements.

3. Manrated spacecraft structures including payloads, equipmentsandexperiments.

b. The factors in clauses 4.1.4, 4.1.5 and 4.3 shall be applied for both thedesignandtestphasesasdefinedinFigure41.

4.1.3 General a. Design factor and additional factors values shall be agreed with the

customer.

4.1.4 Design factor for loads

4.1.4.1 General a. FordeterminationoftheDesignLimitLoad(DLL)theDesignFactorshall

beused,thisisdefinedastheproductofthefactorsdefinedhereafter.

NOTE Robustnessof the sizingprocess is consideredthroughtheDesignLimitLoads(DLL).


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4.1.4.2 Model factor a. A model Factor KM shall be applied to account for uncertainties in

mathematical models when predicting dynamic response, loads andevaluatingloadpaths.

NOTE1 Themodel factor is applied at every level of theanalysis treesystem (Figure42)wherepredictivemodels are used. It encompasses the lack ofconfidence in the information provided by themodel,e.g.hyperstaticity (uncertainty in the loadpathbecauseofnonaccuracyofthemathematicalmodel), junction stiffness uncertainty, noncorrelateddynamicbehaviour.

NOTE2 Whilegoingthroughthedesignrefinement loops,KM can be progressively reduced to 1,0 afterdemonstration of satisfactory correlation betweenmathematicalmodelsandtestmeasurements.

NOTE3 For launch vehicles, at system level, KM is alsocalledsystemmargin.

b. KMvalueshallbejustified.

NOTE Justification can be performed based onrelevant historical practice (e.g. typical valuesof1,2areusedforsatellitesatthebeginningofnewdevelopmentand1,0for internalpressureloads for pressurized hardware), analytical orexperimentalmeans.

4.1.4.3 Project factor a. AspecificprojectfactorKPshallbeappliedtoaccountforthematurity

oftheprogram(e.g.stabilityofthemassbudget,wellidentifieddesign)and the confidence in the specification given to theproject (this factorintegrates aprogrammaticmargin e.g. for growthpotential for furtherdevelopments).

NOTE Thevalueof this factor isgenerallydefinedatsystem level and can be reduced during thedevelopment.

b. KPvalueshallbejustified.

NOTE Justification can be performed based onrelevant historical practice or on foreseenevolutions.

4.1.4.4 Qualification test factor a. ThequalificationfactorKQshallbeappliedforsatellites.

NOTE Forsatellites,thequalificationloadsarepartofthespecifiedloadsandareaccountedforinthedimensioning process. This is different for


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launchvehiclesforwhichQLareconsequencesofthedimensioningprocess.

4.1.5 Additional factors for design

4.1.5.1 Overview Alltheanalysiscomplexityorinaccuraciesanduncertaintiesnotmentionedinclause4.1.4aretakenintoaccountwiththefollowingadditionalfactors.

4.1.5.2 Local design factor a. Alocaldesignfactor,KLDshallbeappliedwhenthesizingapproachor

thelocalmodellingarecomplex.

NOTE This factor accounts for specific uncertaintieslinked to theanalysisdifficultiesor to the lackof reliable dimensioning methodology orcriteriawheresignificantstressgradientsoccur(e.g. geometric singularities, fitting, welding,riveting, bonding, holes, inserts and, forcomposite, layup drop out, sandwich corethicknesschange,variationofplyconsolidationasaresultofdrapeovercorners).

b. KLDvaluesshallbejustified.NOTE1 Justification can be performed based on relevant

historical practice, analytical or experimentalmeans.

NOTE2 For satellites,a typicalvalueof1,2 isused in thefollowingcases:

Compositestructuresdiscontinuities; Sandwich structures discontinuities (face

wrinkling, intracell buckling, honeycomb shear);

Jointsandinserts.NOTE3 Theuseofa localdesignfactordoesnotpreclude

appropriateengineeringanalysis(e.g.KLDdoesnotcover the stress concentration factors) andassessmentofalluncertainties.

4.1.5.3 Margin policy factor a. AmarginpolicyfactorKMPshallbeappliedforlaunchvehicles.

NOTE This factor, used to give confidence to thedesign,covers(notexhaustivelist):

the lackofknowledgeon the failuremodesandassociatedcriteria.


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the lack of knowledge on the effect ofinteractionofloadings.

thenontestedzones.b. KMPvaluesshallbejustified.

NOTE1 Justification can be performed based on relevanthistorical practice, analytical or experimentalmeans.

NOTE2 KMP can have different values according to thestructuralareatheyarededicatedto.

4.2 Loads and factors relationship

4.2.1 General a. QL,AL,DLL,DYL, andDUL, for the test and the design of satellite,

expendablelaunchvehicles,pressurizedhardwareandmanratedsystemshallbecalculatedfromtheLLasspecifiedinFigure41andTable41.

NOTE1 Asa resultof the launchvehiclesatellite coupleddynamic loadanalysis (LCDA)performedduringthe project design and verification phases, theknowledgeof theLL canbemodifiedduring thecourseof theproject, leading toa finalestimationof the loadsLLfinal.Then for finalverification, it isusedasaminimum: QL=KQLLfinal for qualification, andAL=KALLfinal foracceptance

NOTE2 Theyielddesignfactorofsafety(FOSY)ensuresalowprobabilityofyieldingduringloadingatDLLlevel.

NOTE3 The ultimate design factor of safety (FOSU)ensuresalowprobabilityoffailureduringloadingatDLLlevel.

b. Theapplication logicforfactorsofsafetyasgiven inFigure41shallbeappliedinarecursivemannerfromsystemleveltosubsystemlevelorlowerlevelsofassembly.

c. DLLcomputedateachlevelshallbeusedasLLforanalysisattheirownleveltocomputetheDLLforthenextlowerlevelsofassembly.

NOTE ThisisgraphicallyshowninFigure42.

d. For satellite,KQ shall be used only at system level in order to avoidrepetitiveapplicationofqualificationmargins.


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Expendable launch vehicles,pressurized hardware and manned system Test Logic

Common Design LogicSatellitesTest Logic

Limit Loads - LL

Design Limit LoadsDLL

x Coef. A

DYL

x Coef. B

DUL

x Coef. C

x KQ x KA

QLAL

x KQ x KA

QL

AL

Incr

easi

ng L

oad

Leve

l

Figure41:LogicforFactorsofSafetyapplication

Table41:Relationshipamong(structural)factorsofsafety,designfactorsandadditionalfactors

Coefficient SatelliteLaunchvehiclesandpressurisedhardware Manratedsystems

CoefAorDesignfactor

KQxKPxKM KPxKM KPxKM

CoefB FOSYxKLD FOSYxKMPxKLD FOSYxKLD

CoefC FOSUxKLD FOSUxKMPxKLD FOSUxKLD


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System

Limit Loadsat system level

(KQ(1)), KP, KM,

Design Limit Loads

=

Limit Loadsfor subsystem or component

Subsystem or componentKP, KM,

Design Limit Loads

KLD , FOS(KMP(2))

DYL, DUL

KQ(1): for satellite KMP(2): for launch vehicles

Figure42:Analysistree

4.2.2 Specific requirements for launch vehicles a. TheQLshallbedefinedwithacorrectedKQ.

NOTE1 The correction takes into account manufacturingvariabilityanddifficultiesofhavingtestconditionsfullyrepresentativeofflightconditions.

NOTE2 The commonly used method for defining thecorrected KQ is presented in Annex A forinformation.


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4.3 Factors values 4.3.1 Test factors a. ThetestfactorsKQandKAshallbeselectedfromTable42.

Table42:Testfactorvalues

Requirements CommentsLoadtype

Vehicle KQ KA

Satellite 1,25a 1

Launchvehicle 1,25correctedb 1orJpc

TypicalvaluetobeconsideredfordimensioningareJp=1,05to1,1

Launchloads 1,4

Globalflightloads

ManratedS/C

Onorbitloads

1,51,2

Internalpressure inconformancewithECSSEST3202 i Applicableforsatelliteandlaunchvehicles

Satellite 1,25a,e 1 Dynamiclocalloadsd

Launchvehicle 1,25e N/A

Hoistingloadsf Satellite 2 N/A

Hoistingloadsg(failsafe)

Satellite 1 N/A

Storageandtransportationloads

Satellite

localtransportationandstorageloads

othertransportationloads

2

1,4

N/A

Satellite 1 1Thermalloadsh

Launchvehicle 1 1

a AhighervaluecanbespecifiedbytheLaunchvehicleAuthorityorthecustomer.

b Seeclause4.2.2.

c Jpistheprooffactorforpressurizedstructure.

d Localloadsaresystemlevelloadscomputede.g.onunits,appendages,equipments,fixturesduringdynamicanalyses.

e Thevalueappliesforqualificationtestsunderlocalloadconditions.Ahighervaluecanbespecifiedforspecificpurposes.

f Nationallawscanspecifyhighervalues.

g Failsafemeansincaseoflossofoneofthehoistingslings.Inthiscase,thelimitload(LL)isdeterminedbyusingpeakdynamicloadduetothefailureofthehoistingsling.

h Thermalloads(i.e.mechanicalloadofthermoelasticorigin)aretakenwithaqualification/acceptancefactorequalto1byusingtemperatureandgradientslevelsatqualification/acceptancelevelswherethequalification/acceptanceleveltemperatureincludesthermalpredictionuncertaintyplusaqualification/acceptancetemperaturemargin.

i KQisdefinedasBurstFactorandKAisdefinedasProofFactorinECSSEST3202.


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4.3.2 Factors of safety

4.3.2.1 Metallic, FRP, sandwich, glass and ceramic structural parts

a. The factor of safety for metallic, FRP, sandwich, glass and ceramicstructuralpartsshallbeselectedfromTable43.

b. Forsatellitesandmanratedspacecraft,thefactorsprovidedinTable43shallapplyforalladditiveloadsincludingthermalinducedloads.

c. For satellites andman rated spacecraft,when loads including thermalinducedloadsarerelieving,bothFOSUandFOSYshallbe1,0orless.

NOTE SeeECSSEST32.

d. Forexpendablelaunchvehicles,FOSUandFOSYassociatedwiththermalinducedloadsshallbe1,0.


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Table43:Factorsofsafetyformetallic,FRP,sandwich,glassandceramicstructuralparts

Requirements

Structuretype VehicleFOSY FOSU

FOSYverificationbyanalysisonly

FOSUverificationbyanalysisonly

Satellite 1,1 1,25 1,25 2,0

Launchvehicle 1,1 1,25 SeeNotec 2,0

Metallicparts

ManratedS/CLaunchOnOrbit

1,251,1

1,41,5

SeeNotec SeeNotec

Satellite N/A 1,25 N/A 2,0

Launchvehicle N/A 1,25 N/A 2,0

FRPparts(awayfromdiscontinuities)

ManratedS/CLaunchOnOrbit

N/AN/A

1,52,0

N/AN/A

SeeNotec



FRPparts(discontinuities)a

ManratedS/C N/A 2,0b N/A SeeNotec



Sandwichparts:

facewrinkling

intracellbuckling

honeycombshear ManratedS/C N/A 1,4 N/A SeeNotec


Launchvehicle N/A SeeNotec N/A SeeNotec

Glassandceramicstructuralparts

ManratedS/C N/A 3,0 N/A SeeNotec

a e.g.:holes,frames,reinforcements,steepchangeofthickness.

b ThisvalueisforconsistencywithNASASTD5001andalreadyincludeaKLDfactor.

c Nocommonlyagreedvaluewithinthespacecommunitycanbeprovided.


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4.3.2.2 Joints, inserts and connections a. The factorof safety for joints, inserts and connections shallbe selected

fromTable44.

Table44:Factorsofsafetyforjoints,insertsandconnectionsRequirements

Structuretype VehicleFOSY FOSU

FOSYverificationbyanalysis

only

FOSUverificationbyanalysis

only

SatelliteN/AN/AN/A

1,25N/AN/A

N/A1,251,25

2,0N/AN/A

LaunchvehicleN/A1,11,1

1,25N/AN/A

N/A N/A

Jointsandinserts:a

Failure

Gapping

Sliding

ManratedS/C SeeNotec1,41,41,4

SeeNotec SeeNotec

Satellite SeeNotec 2,0 SeeNotec SeeNotecElastomersystemandelastomertostructureconnectionb

Launchvehicle SeeNotec 2,0 SeeNotec SeeNotec

a Thesefactorsarenotappliedontheboltspreloadseethreadedfastenersguidelineshandbook(ECSSEHB3223).

b Analysisandtestareperformedtoshowthatthepossiblenonlineardynamicbehaviouroftheelastomerdoesnotjeopardizethesatellitestrengthandalignment.

c Nocommonlyagreedvaluewithinthespacecommunitycanbeprovided.

4.3.2.3 Buckling a. The factorofsafety forglobaland localbucklingshallbeselected from

Table45.

NOTE The factor of safety does not cover the knockdown factors commonly used in bucklinganalysesseeBucklinghandbook(ECSSEHB3224).


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Table45:FactorsofsafetyforbucklingRequirements

VehicleFOSY FOSU

FOSYverificationbyanalysis

only


Satellite SeeNotea 1,25 SeeNotea 2,0

Launchvehicle

Global

Local

N/A

1,1

1,25

1,25

SeeNotea

2,0

2,0

ManratedS/C SeeNotea 1,4 SeeNotea N/A

a Nocommonlyagreedvaluewithinthespacecommunitycanbeprovided.

4.3.2.4 Pressurized hardware a. The factorofsafety forpressurizedhardware,engine feeding lines,and

tank pressurisation lines shall be selected from Table 46 for themechanicalloadsexcepttheinternalpressure.

NOTE1 For internal pressure loadings and loadscombination,seeECSSEST3202.

NOTE2 PressurizedhardwareisdefinedinECSSEST3202.

Table46:FactorsofsafetyforpressurizedhardwareRequirements

VehicleFOSY FOSU

FOSYverificationbyanalysisonly


Satellite 1,1 1,25 SeeNotea SeeNotea

Launchvehicle 1,1 1,25 SeeNotea SeeNotea

ManratedS/C 1,25 1,4 SeeNotea SeeNotea

a Nocommonlyagreedvaluewithinthespacecommunitycanbeprovided.


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Annex A (informative) Qualification test factor for launch vehicles

InEuropean launchvehicleprograms, theQL tobe implementedduring thetestisdefinedwithacorrectedKQfactor,derivedbylocationandfailuremode.

KQismodifiedbycorrectingfactorssuchas:

( )

+=KK

1KKKFOSYKQ Tadjmin for loading at yield load

( )

+=KK

1KKKFOSUKQ Tadjmin for loading at ultimate load

Takingintoaccountthefollowingpoints: Theactual thicknessofqualificationmodelversus thicknessused

forsizing.ThisisdonethroughtheuseofthecorrectingfactorKminwhich accounts for the effect of the thickness on the structurestrength. Itcorresponds to theratioof the thicknessmeasuredonthetestspecimentothedimensioningthickness. Kmin is only applicable to metal structures, for other structures,Kmin=1.0isused.

Theadjacentstructuresinfluenceonthestressfieldbetweenflightandtestconditions.ThisisdonethroughtheuseofthecorrectingfactorKadjwhichaccounts for the influenceofadjacentstructuresnotpresentduringstatictests.

o Iftheadjacentflightstructuresaresimulatedduringstatictests,Kadj=1,0isused.

o Elsewise,Kadjisdeducedastheratioofthestressstate(flight)computedinflightconfigurationtothestressstatecomputedintestconfiguration(test)increasedbytheoverfluxfactorusedforthedesign.

),0,1max( overfluxtest

flightadj kK =

Effectof thermalgradient stress.This isdone through theuseofthecorrectingfactorKTwhichisdefinedastheratiooftheincreasein the stress due to the local thermal gradient to the stresscorrespondingtonolocalthermalgradient.


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The effect of temperature onmechanical characteristics (Youngsmodulus, strength). This is done through the use of thecorrecting factor K which is the ratio of the mechanicalcharacteristicsconsideredatflightoperatingtemperatureCflighttotheonesattesttemperatureCtest.

test

flight

CC

K

=

TheinfluenceofAvaluesforsizingandmoreprobablevaluesforthematerial constitutiveof the qualificationmodel.This isdonethroughtheuseofthecorrectingfactorK.Iff(Ci) isthefunctiontranslating theeffectof characteristicCion the failuremode, thecorrecting factor K is defined as the ratio of f(Ci) for thecharacteristicvalueused fordesign to f(Ci) for the characteristicvalueofthetestedspecimen.

( )( )testi designiCfCf

K =

If several characteristics C1, C2, are affecting the consideredfailuremode,Kisdefinedas:

( )( ) ( )( ) ( )( )testn designntest2 design2test1 design1 CfCf

.....Cf

CfCf

CfK =

Thecorrectingfactorsaredefinedandagreedwiththecustomer.


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Bibliography

ECSSSST00 ECSSsystemDescription,implementationandgeneralrequirements

ECSSEHB3223 SpaceengineeringThreadedfastenershandbook

ECSSEHB3224 SpaceengineeringBucklinghandbook.

NASASTD5001 Structuraldesignandtestfactorsofsafetyforspaceflighthardware(June21,1996)

A5SG1X10ASAI(issue5.12,Aprilthe8th;2003)

Structuredesign,dimensioningandtestspecifications

Change log1 Scope2 Normative references3 Terms, definitions and abbreviated terms3.1 Terms and definitions3.2 Terms specific to the present standard3.3 Abbreviated terms

4 Requirements4.1 Applicability of structural factors of safety 4.1.1 Overview4.1.2 Applicability4.1.3 General4.1.4 Design factor for loads4.1.4.1 General4.1.4.2 Model factor4.1.4.3 Project factor4.1.4.4 Qualification test factor

4.1.5 Additional factors for design4.1.5.1 Overview4.1.5.2 Local design factor4.1.5.3 Margin policy factor

4.2 Loads and factors relationship 4.2.1 General4.2.2 Specific requirements for launch vehicles

4.3 Factors values4.3.1 Test factors4.3.2 Factors of safety4.3.2.1 Metallic, FRP, sandwich, glass and ceramic structural parts4.3.2.2 Joints, inserts and connections4.3.2.3 Buckling4.3.2.4 Pressurized hardware

Bibliography

Documents

ECSS-E-ST-32-10C_Rev.1(6March2009).pdf