Question

A rotating-beam specimen is made of AISI 1018 CD steel. Estimate its

(a) Endurance limit,
(b) Fatigue strength at 1000 stress cycles, and
(c) Fatigue strength at 200,000 stress cycles. Use SI units.

Answer 1

a.
`S_(e)`= 220 MPa

b.
`(S_(f) )_(1000) = 220.6 Mpa`

c.
`(S_(f) )_(200000) = 91.06 MPa`

Step-by-step explanation:

AISI 1018 Cold drawn steel mechanical properties

`S_(ut)=440 MPa`

For Steel

`S_(e)`= rotating beam specimen endurance limit = 0 .15
`S_(e)`

a.

for Endurance limit,

`S_(e)`= 0.5 x 440

`S_(e)`= 220 MPa

b. For Fatigue strength at 1000 stress cycles,

`S_(e)`= 220 MPa

`S_(ut)=440 MPa`

N = 1000

Ф.f=
`(S_(ut) +345)Mpa=785Mpa`

`b=( -log(785/220))/(log(2 .1000))`

b=-0.167

Now equation for S-N line

`(S_(f) )_(N) = \phi_(f) (2N)^(b) =785(2N)^(-0.167)`

`(S_(f) )_(1000) =785(2*1000)^(-0.167)`

`(S_(f) )_(1000) = 220.6 Mpa`

c.

`(S_(f) )_(200000) =785(2*200000)^(-0.167)`

`(S_(f) )_(200000) = 91.06 MPa`