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Verify each item of Eq. 9.4, starting from any of Eqs. 9.1 to 9.3 or preceding items of
Eq. 9.4.
Write definitions in your own words for point stress o, nominal stress S, and the product
4,S. Give an example of a situation where o = S, and also give an example where
oS.
For an S-N curve of the form of Eq, 9.5, two points (Ni, 01) and (Np, 02) are known,
(a) Develop equations for the constants C and D as a function of these values.
() Apply your result from (a) to the data in Fig. 9.5 for Ny <10® cycles, evaluating C and
D to obtain an equation that gives a reasonable representation of these data
The steel 50CrMod can be assumed to have an S-N curve of the form of Eq. 9.6. Some
fatigue test data for unnotched specimens under axial stress, with zero mean stress, are given
in Table P9.4.
(a) Plot these data on log-log coordinates, and determine approximate values for the
constants A and B.
(b) Obtain refined values for A and B, using a linear least-squares fit to log Ny versus
loga,. Then calculate a, and b for Bq. 9.7.
Table P9.4
Oa MPa Ny eyeles
615 14000
578 55000
600 58000
559 61.000
563 165000
540 270000
Soutee: Data in (Baumel 90].
Proceed as in Prob. 9.4, but use the data in Table P9.5 for unnotched, axially loaded specimens,
of 2024-T3 aluminum tested under zero mean stress.
Table P9.5
Oa MPa Ny cycles
331 43.000
276 112.000
241 172000
207 231000
190 546000
179 1165 000
Source: Data in [Baumel 90].
