Failure Investigation Question 1:IsTheProblem BatchRelated? Allfailedswitches plusothernon-faulted unitswerecharacterized dimensionally. Allinstallation fitswere normal andcorrect. Racesandballsfromthetwoundamaged failedunitswerecompliant todesign. Retainers fromallofthefailedunitswereexamined andcompared withnewretainers fromthesameand fromdifferent manufacturing lots.Allretainers conformed todesign. Particular attention waspaidtothe ballpocket openings asthesedimensions influence thesnap-over forceoftheassembly. Allsamples weresimilar insize(albeitnearthewideendofthetolerance band).Theballpocketopenings ofthe faulted retainers showed novisiblewearordeterioration andwereindistinguishable fromnewmaterial evenunderhighmagnification. Nodefectorbatchdependant issues werefound.Noindication of progressive faultasmightresultfromwearorfatiguewasfound. Question 2:IsRetainer Desiqn Deficient? Several experiments wereexecuted todetermine theforcenecessary todislodge theball-retainer andto assess thecharacteristics ofapartially disassembled bearing. Theforcenecessary tofullyremove the retainer ranged from5to7N.Giventheretainer massof171mg,anacceleration of3,000g'swouldbe required tosimplyejecttheretainer whichismuchhigherthatanycalculated vibration induced condition. Intermsofpartialdisassembly, itwasalsoobserved thatthefirst(lowest energy) quasi-stable dislocated stateoftheretainer entailed oneballbeingfullydisengaged fromitscagepocket. Suchaballwouldnot likelyreturntoitsoriginal position indynamic conditions, butratherwouldtendtoadvance onanadjacent ballandfurtherdisengage thecagefromthebearing. Inthisrespect smallrotaryoscillations around the equilibrium position mayfavorthefailure. Theforcenecessary toattainthispartialejection isbetween 1 and2Nand,whilelowerthanthatrequired forstraight ejection, itisamoment forceapplication. Sucha condition isequally asremote asthestraight ejection. Question 3:CanVibration Induced LoadsJustifyTheFault? AsseeninQuestion 2above, accelerations simply resulting fromthehighvibration inputscannot adequately explain thecageejection. Regardless, thereisavibration testfailurehavingfiveoccurrences inanapplication seemingly differing littlefrompriorsuccessful applications. Todealeffectively with vibration induced loads,detailed structural andbearing analyses follow. Thestructural analysis usesanalytical andmeasured datatoresolve effectsofcrossaxiscoupling and hammering thereby determining, asaccurately aspossible, accelerations andbearing loads.Thebearing analysis evaluates bearing deflections basedontheseloadconditions. Together, theseanalyses maybe applied todescribe thecomplex motions involved andtoidentify resonant conditions thatmayexacerbate thefaultcondition. Structural Analysis Foranalysis purposes themobile package displacements areseparated intodisplacements duetothe free-body motionanddisplacements duetostructural deformation. Bearin.q AxialLoads Thefree-body motionoftherotarypackage consists inalongitudinal translation andarotation around the bearing axis.Inthecaseofthelongitudinal translation, thesimplified system describing themotion isa single-degree-of-freedom (SDOF) masssupported onanidealspring. Thestiffness ofthisspring(the magnetic axialpreload fromtheactuator) isdetermined bymeasurement tobe192.3N/m.Low-level sine vibration measurements ofthetotalpackage revealthattheresponse isdominated bythehousing response andhasaminimum natural frequency of767HzonY-axis(coordinate system presented in Figure2)andnatural frequencies of1700Hz fortheothertwoaxes.Thisisduetothemuchhigher housing stiffness andmasswhencompared tothemobile-package &magnetic-spring system. NASA/C P--2002-211506 297