Lutz Beyland Composite Design Engineer German Aerospace Center DLR Institute of Composite Structures and Adaptive Systems Elisabeth Ens RWTH Aachen ICCS20 International Conference on Composite Structures ID: 1043629
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1. Bolted joints with radial pretension for thick-walled composites structuresLutz Beyland, Composite Design Engineer,German Aerospace Center (DLR)Institute of Composite Structures and Adaptive SystemsElisabeth EnsRWTH AachenICCS20, International Conference on Composite Structures4-7 September 2017 – CNAM, Paris, France
2. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 2OutlineState of the art bolted joints in thick walled laminatesConcept of bolted joint with radial pretensionAnalytical approachFE-CalculationBearing testsConclusion and Outlook
3. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 3Bolted joints for thick laminates - state of the artFields of application for many decadesmulti-stage rockets for transportation of satellitesconnection of aircraft wing and fuselageroot connection of rotor blades of wind turbinesFailure modesTensionShear OutCleavageBearingPayload adapter Ariane 5 [DIEM]T-Bolt connection for rotor blades [HAU]
4. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 4Problems of state of the art bolted jointsJoint stiffness and wear depend on bolt-hole clearanceAvoiding big bolt-hole clearance leads toHigh effort for precise drilling of boreholeNeed for reaming / drilling of both joint parts in one processBig ClearancePPLow Stiffness, high wearPPHigh Stiffness, medium wearSmall / No ClearanceRadial PretensionPPVery high stiffness, low wear
5. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 5Concept of radial pretensionClamping bush overcomes clearance and creates a radial pretension between bolt and bore holeRadial pretension by axial tightening of inner and outer ringOuter ring of clamping bush is slatted >> Diameter increase of 1 mm possible2 - No Clearance3 - Radial Pretension1 - ClearanceInnerringOuterringBoltPlate with bore holeOuter ringInner ringOuter ringInnerringClamping bush [MÄDLER]
6. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 6Research topics on bolted joint with radial pretension Analytic modelto describe stress state around bore holeFE modelto validate mathematical model andfor detailed analysisBearing testsStatic and fatigue strength
7. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 7Analytic approachPretension [Timoshenko] Bolt load [Zhang] Superposition
8. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 82D FE model - setupFE-Software: Ansys Workbench 18.1Boundary conditionsSymmetry at midplaneFixed support of disk‘s peripheral surfaceBolt load as distributed force on bolt’s peripheral surfaceRadial pretension by thermal expansion of boltFrictionless contact between bolt and holeMaterialLinear-elastic modelDisk: GFRP, quasi-isotropic stiffnessBolt: SteelFixedsupportBolt loadThermal expansionDiskBoltSymmetry
9. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 92D FE model - resultsRadial stressParameterVariableValueUnitRadius bore holea32,5mmOuter radius diskb800mmYoung‘s Modulus diskE27GPaPoisson's ratio diskν0,343-Pretensionpi270MPaRadial expansion (caused by pretension)u00,5mmBolt loadp28kN/mmUse case
10. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 10Comparison of analytical and FE model Circum-ferential pathStresses at bore hole (circumferential path)σrad maximum difference: 2 MPaσtan maximum difference: 5 MPaConclusion: Analytical model is accurate for stresses at bolt hole
11. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 11Comparison of analytical and FE model Radial pathStresses at bore hole (radial path)σrad maximum difference: 16 MPa (~7%)σtan maximum difference: 20 MPa (~17%)Conclusion: Analytical model is sufficient for stresses at whole disk
12. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 12Effect of friction on stress distribution – 2D-FEFriction strongly influences stress distributionCoefficient of friction µ between bolt and hole is not well knownLiterature [Cuntze] suggestsµ = 0,1 – 0,3>>> µ = 0,1 chosenNearSlidingStickingContact statusµ = 0 µ = 0,1 µ = 0,5 Circum-ferential path
13. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 13Effect of pretension on stress distribution – 2D-FEAmount of pretension significantly influences both radial and tangential stressHigh pretension avoids clearance under bolt load >> no tangential stress peak atMedium pretension results in minimum overall tangential and radial stresses SzenarioPretensionpi [MPa]Expansionu0 [mm]High pretension2700,5Medium pretension1350,25No pretension00 Circum-ferential path
14. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 14Bearing test setupSpecial 3-Point bearing test setupLaminate thickness t = 10…20 mmMaximum static load: F = 500 kNMaximum fatigue load: -50 kN < F < +200 kNSpecimen GFRP[+45 / -45 / 0 / 90]5sBoltd = 40 mmBore hole for fixationBearing failure
15. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 15Clearance fit vs. radial pretensionClearance fitClamping bush for radial pretensionClearance = 0,1 mmRadial expansion u0 = 0,4…0,8 mm
16. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 16Results in bearing strength Bearing strength F… bolt load at failured… hole diametert… laminate thicknessStatic bearing strength with radial pretension -15% compared to clearance fitFatigue bearing strength with radial pretension +40% compared to clearance fitHigh pretension results in slightly higher fatigue strength
17. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 17Conclusion and OutlookConclusionAnalytic model for bolted joints with radial pretension is found and validated by FE-calculation (neglecting friction and cleavage)Friction has a big impact especially on tangential stressesRadial pretension results in smooth distribution of stresses around the bore holeBearing tests with radial pretension show an increase in fatigue strength, but a decrease in static strengthOutlookDetailed understanding of bearing failure with radial pretensionPrediction of failure load from FE-calculation>>> failure criteria for bearingBearing tests with different pretensions>> evaluation of optimum pretensionBearing tests with combined radial and axial pretension
18. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 18MANY THANKS FOR YOUR ATTENTION !Lutz Beyland, Composite Design Engineer,German Aerospace Center (DLR), Institute of Composite Structures and Adaptive SystemsLilienthalplatz 7, 38108 Braunschweig, GermanyLutz.Beyland@DLR.deDO YOU HAVE ANY QUESTIONS ?
19. > ICCS20 > Beyland > 05.09.2017DLR.de • Slide 19References[DIEM]Diem, H.: Tragfähigkeit von Bolzenverbindungen in dickwandigen Faserverbundstrukturen; Dissertation; TU München; 19.2.2007[HAU]Hau, E.: Windkraftanlagen: Grundlagen, Technik, Einsatz, Wirtschaftlichkeit, Springer Berlin Heidelberg, ISBN 978-3-540-72150-5[MÄDLER]Mädler GmbH: Spannsätze COM-AS Bohrung 19 bis 100mm; http://www.maedler.de/product/1643/1621/spannsaetze-com-as-bohrung-19-bis-100mm; accessed on 30.8.2017[TIMOSHENKO]Timoshenko, S.: Theory of Elasticity; McGraw- Hill; 1934[ZHANG]Zhang, K.-D.; Ueng, C. E.: Stresses Around a Pin-loaded Hole in Orthotropic Plates; Journal of Composite Materials 18 (1984), No. 5, p. 432-446[CUNTZE]CUNTZE, R.; Das Versagensmoduskonzept, ein praktikables Auslegungswerkzeug bei neuen Leichtbauwerkstoffen“; Handout, Dresdner Leichtbausymposium, 7.-9. June 2001
20. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 20Anhang
21. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 21Lösungsraum für segmentierteRotorblätterJOULE IIIEnerconE126GamesaInnobladeIndeol / CENERModular Wind EnergyJOULE IIIConnection principleDetachableNon-DetachableBolting in longitudinal directionBolting in transversal directionBolting of pieces with a large overlapWelding of thermoplastsBonding of thermosetsT-boltsMetallicinsertsForm-fitForce-fitConnection tubesBolting of shear webSingle lapMulti lapSingle lapMulti lapMegawindJOULE IIIDEBRA-25T-boltsMetallicinsertsConnection tubesMulti lap
22. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 22Wo teilen?0.2100.30.40.50.60.70.8TransportationExtra mass = dynamic loadsSpar cap loadsSecondary loadsBig extra mass = extra costLittle spaceBoltingBonding
23. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 23Konzept „Stegverschraubung“Schnitt A-AWurzel-GurteTipGurteWurzel-StegTip-StegzxSchraube mit Mutter (ca. M36)Stegbuchse WurzelsegmentStegbuchse TipsegmentStegbuchse TipsegmentStegbuchse Wurzelsegmentca. 5mDetail ZyxWurzel-GurtWurzel-StegeTip-StegeTip-GurtyxSchnitt B-BzyDetail ZAABB
24. CAD-Modell „Stegverschraubung“ in Nordex-Rotorblatt NR58.5tipseitige VerschraubungwurzelseitigeVerschraubung> ICCS20 > Beyland > 05.09.2017DLR.de • Folie 24
25. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 25Segmentiertes Rotorblatt – Testpyramide (10-2016)
26. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 26Lochleibungstests BiLoKlebstoff>> verklebte Probe ohne FlanschSpannbuchse>> verspannte Probe>> gesteckte ProbeSpielpassung
27. > ICCS20 > Beyland > 05.09.2017DLR.de • Folie 27Rax-Buchse – Funktionsdemonstrator + Patentanmeldung