5491

5151

كارشناسي ارشد

طراحي كاربردي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1389

ده،78ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

محمودرضا فروزان

محمد مشايخي

4/8/89

محسن اصفهانيان، محمود كدخدايي

مهندسي مكانيك

ID5151

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Service life prediction of a helicopter main rotor shaft Mohammad bagheri nouri mhmmd bagheri@yahoo com Date of submission 2010 04 28 Department of mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Mohammad Reza Forouzan forouzan@cc iut ac ir Abstract Subject of this dissertation is the life prediction of a helicopter main rotor shaft since application ofDamage Tolerance concepts on the shaft is not possible for practical reasons such as limitations due toinspectability according to FAR regulation the safe life approach was used Because the shaft loading isnon proportional and the material has low ductility the combinations of the amplitude of alternating shearstress with maximum normal stress on the critical plane should be used as controlling parameter for fatiguedamage Therefore for life prediction findley criterion was applied The Loading of the shaft effect of several components like tail plane tail rotor and hub on the loadingwas studied Because applied torque variation with the blades rotation is different from the applied thrustforce variation two separate finite element analyses for each of the loading was done Because of shaftsymmetry one thirtieth of the shaft that includes a tooth of the spline was modeled For life predictionaccording to findley criterion an APDL code was developed in ANSYS software Because of the linearmaterial behavior the code uses superposition principle and results of the two finite element analyses toattain stress tensor variation with the blades rotation in each node The code applies a load factor of 2 5 thatensures us about the most severe manoeuvres The code uses the minimum circumscribed circle approach tocalculate the amplitude of shear stress The code determines the critical plane according to findley criterionand compares the damage parameter with material specifications to predict the life The output of this code islife contour of the elements attached to the selected nodes To find the critical node the life was calculated in extremum of components of stress tensor The criticalnode is in the root of spline tooth The shaft life was calculated 4389542 revelutions equal to 250 flight hoursfor the most critical manoeuvres in this node Life contour of the elements around this node was plotted Forplotting fatigue sensitivity in the critical node the loading was changed with coefficient of 0 5 to 1 5 andfatigue result variation was observed Fatigue sensitivity analysis implied that if stresses were decreased twotimes the life would be infinite and if stresses were increased two times the life would decrease 66 percents Replacing the material with AISI SAE 4340 that has ultimate tensile strength of 125 Ksi and AISI SAE 4130with ultimate tensile strength of 117 Ksi leads to life reduction of 99 percents and 55 percents respectively Key words life prediction non proportional loading critical plane approach helicoptermain rotor shaft

محمودرضا فروزان

محمد مشايخي

محسن اصفهانيان، محمود كدخدايي