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  • March 2005

    NASA/TM-2005-213525

    X-43A Rudder SpindleFatigue Life Estimate and Testing

    Edward H. GlaessgenLangley Research Center, Hampton, Virginia

    David S. DawickeAnalytical Services and Materials, Inc.Langley Research Center, Hampton, Virginia

    William M. JohnstonLockheed Martin Engineering and SciencesLangley Research Center, Hampton, Virginia

    Mark A. JamesNational Institute of AerospaceLangley Research Center, Hampton, Virginia

    Micah SimonsenCorrelated Solutions, Inc., Columbia, South Carolina

    Brian H. MasonLangley Research Center, Hampton, Virginia

    https://ntrs.nasa.gov/search.jsp?R=20050136675 2018-05-12T18:27:33+00:00Z

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  • National Aeronautics andSpace Administration

    Langley Research Center Hampton, Virginia 23681-2199

    March 2005

    NASA/TM-2005-213525

    X-43A Rudder SpindleFatigue Life Estimate and Testing

    Edward H. GlaessgenLangley Research Center, Hampton, Virginia

    David S. DawickeAnalytical Services and Materials, Inc.Langley Research Center, Hampton, Virginia

    William M. JohnstonLockheed Martin Engineering and SciencesLangley Research Center, Hampton, Virginia

    Mark A. JamesNational Institute of AerospaceLangley Research Center, Hampton, Virginia

    Micah SimonsenCorrelated Solutions, Inc., Columbia, South Carolina

    Brian H. MasonLangley Research Center, Hampton, Virginia

  • Available from:

    NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS)

    7121 Standard Drive 5285 Port Royal Road

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  • 1

    Abstract

    Fatigue life analyses were performed using a standard strain-lifeapproach and a linear cumulative damage parameter to assess theeffect of a single accidental overload on the fatigue life of theHaynes 230 nickel-base superalloy X-43A rudder spindle.Because of a limited amount of information available about theHaynes 230 material, a series of tests were conducted to replicatethe overload and in-service conditions for the spindle andcorroborate the analysis. Both the analytical and experimentalresults suggest that the spindle will survive the anticipated flightloads.

    Nomenclature

    b = fatigue strength exponentc = fatigue ductility exponentE = elastic modulus (assumed to be isotropic)Kb = notch sensitivity factorKI = mode I stress intensity factorKIC = mode I fracture toughnessKt = stress concentration factorN = number of cyclesNf = number of cycles to failureR = fatigue stress ratio (also, fillet radius)RT = room temperatureea = cyclic strain amplitudeef = fatigue ductility coefficientei = Principal strain (i=1,2,3)eij = strain (i,j=1,2,3)seff = von Mises equivalent stresssf = fatigue strength coefficientsi = Principal stress (i=1,2,3)sm = mean effective stresssu = ultimate stresssys = yield stresstij = shear stress (i,j=1,2,3)

  • 2

    Introduction

    In the summer of 2004, during preparations for flight of the X-43A, one of the rudders onthe vehicle was unintentionally overloaded. The X-43A, an unmanned flight test vehiclethat will make a single hypersonic flight in late 2004, is shown in Figure 1. Previousfinite element analysis determined that the highest stresses and strains during theoverload existed at an O-ring groove in the rudder spindle, as shown in Figure 2 [1]. Atthe request of the X-43A Program Office, a combined analytical and experimentalassessment was planned and executed to determine whether or not the static overloadwould result in premature failure of the rudder spindle during flight test.

    Although a fatigue crack growth assessment was originally considered, it was discountedbecause the magnitude of the overload stresses, residual stresses and plastic strains werelikely to violate linear elastic fracture mechanics (LEFM) assumptions. Hence, a strain-life approach including mean stress effects [2] was used to assess the remaining life ofthe rudder spindle. The strain-life approach is based on the assumption that the fatiguelife of notched components can be related to the fatigue life of small unnotchedspecimens subjected to the same strains as the material at the notch root. Because severalimportant items of information were unknown in this analysis, several assumptions weremade to facilitate the calculation of the fatigue life. These assumptions had a significanteffect on the life predictions.

    Additionally, testing was performed to ensure that the assumptions of the strain lifeanalysis provided a conservative margin of safety for the rudder spindle during in-serviceloading. A test plan (shown in Appendix A) was developed to experimentally simulatethe overload condition as well as the fatigue cycles.

    This report documents the assumptions used in the analysis, the life analysismethodology and results, the configuration of the test specimens, the test method and theresults of the tests.

    Figure 1. X-43A vehicle

    Length=12 (3.7 m)Width=5 (1.5 m)Height=2 (0.6 m)

  • 3

    Fatigue Life Analysis

    Known, Speculative and Assumed Information

    This section summarizes the known and speculative information, assumptions madeabout the material behavior, and assumptions used in the finite element and fatigue lifeanalyses.

    Known Information The X-43A rudder shaft was inadvertently overloaded to an unknown torque. Upon unloading, the rudder had a permanent rotation of approximately 2.5 to 3. The shaft material was Haynes 230 nickel-base superalloy. The shaft was hollow with an outside diameter of 0.92 in. and an inside diameterof 0.1875 in. The shaft configuration included an O-ring groove with a diameter of 0.8 in. anda fillet (notch) radius of 0.015 in.

    Speculative Information The O-ring groove was assumed to be the critical location on the rudder shaftafter the overload. The initial state of the O-ring groove was assumed to be crack and defect free. O-ring groove stress levels due to the overload were determined accurately fromelastic-plastic finite element analyses [1]. O-ring groove stress levels due to in-service, cyclic loads were determinedaccurately from elastic-plastic finite element analyses [1].

    Figure 2. von Mises stress in rudder [1]

    Highest stress at O-ring groove

    Spindle

    Von MisesStresss

  • 4

    The operational temperature of the shaft is 400F. This value was the highestmeasured temperature during a prior test. However, the thermocouple failedbefore completion of the test, so the actual value is unknown.

    Material Assumptions (Data from the Manufacturer [3,4]) The tensile modulus, yield stress and ultimate stress are: E = 30,600 ksi, sys =56.9 ksi, su = 124.9 ksi, respectively [3]. The tensile properties reported by the manufacturer, and based on uniaxialtesting, were appropriate for modeling cyclic torsional loading. The uniaxial strain-life curves that were developed from axial data can be usedto accurately predict failure under torsional lo

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