Question

A 1.5 in diameter specimen of AISI 4340, quenched and tempered at 600 deg F is subject to fullyv-reversed axial loading. The specimen has a machined finish and is expected to operate at a temperature range of 20 deg F to 130 deg F. For a reliability of 99.9%, determine the fatigue strength corresponding to 300,000 cycles of operation.

Answer 1

Matetial o f Specimen : AISI 4340 (Quenched 옥 tempered at 600F) Specimen is subjected to reverse axfal loading aeter oF Specimen 15 in 38 1 mm m Materiol property Databook for given material Sut = 1000 MPa For steels rotating beamtest= 0.5 sut-500 M Ra (Se) D ModiFication factor for surface -finish (Ka)- aSut) for machine finish a-4.5) , b=-0.26s- 2) Modification factor for size (kb) DKb=0.8 for dia < 50mm 3) Modification factor for given loading condition (Ke 4) Reliability factor kd=0.753 for 99.9% reliability E) Modification fachor for considering the operating temperature Ke o 85 for reversed axial loading kT 0.975 t 0.432 C10-3) TF 0.975 t 0 432(10 )x (o 1303- 0-535u012 x 13 04 Corrected Endurance strengths ka kb Kc k KT.Se (Se) 0,723 x 0.8 x 0.85 x 0.75 3x1 x 500 185-102 MPa

S-N S diaram of Materfal: log 1o ( 0.9Sut) 2.954 10(Se) = loglo(185-102): 2.267 lo(0)- 5.477 lo log idos似2954 5477 6 Applying Similar triangle 1o AACE and AABD AB AC BD EC 2.954 Iogo F5.477-3 6-3 2.954 2.267 logio(F): 2.386 =10 _ = 243.22 MPa 02386 .. . Fatigue Strength corresponding to life of 3지。scycles 243.22 MPa、