Question

Question 1 A flat leaf spring made from AISI 1020 cold drawn steel has fluctuating stresses between the maximum stress, Smar of 360 MPa and minimum stress, Smn of 160 MPa; applied for a duration of 8 (10) cycles. The AISI 1020 CD material has a fully corrected endurance strength of Sa 5 175 MPa, yield strength, S, of 390 MPa and ultimate strength, S of 470 MPa. Assume that the fatigue strength fraction, f of 0.9 Using Miner's method, predict how much longer will the spring survive when the load is then changed to Smar of 320 MPa and Smn of-200 MPa. Apply the modified Goodman citerion for failure in evaluating the average stress for failure. (15 markah/marks)

Answer 1

iven Su= 470 MPo Syc390 MPA, Se IT5 MPa first loadeng 360 +160- 260 MPa o mia 360-16 Os 100 good (rae(a 1-260 410 Ca 233-8MPa >se firnite life (Sulo9 (470] l022.5 MPa Se bz- log/.410) T5 0.1211 223 8 1022.5 N = cyeks second oadong NE 145,120 (G 232a0-200'-60 MPa (ra 3 20 200 260 MPo (alea= 260 - 298 MPa method Oi271 298 022.5 cyeles Na = 15,58o .N2 80,D00 45920 5520 gyceles Y =7000