Best fit S/N curves for 7050-T7451

Question

Best fit S/N curves for 7050-T7451

feajob (Aerospace)

(OP)

10 Apr 22 19:23

Hi Guys,
I recently noticed that there is significant difference between the predicted life with S/N curves shown in Figures 3.7.5.2.8(b)and 3.7.5.2.8(e) in MMPDS-09. Both of them are "for unnotched 7050-T7451 plate, long transverse direction, t/4 specimen locations". The second one is giving very conservative results comparing to the first one. I would like to know how we can explain this significant difference? I also noticed that these curves are not shown in MMPDS-15.
Thanks,
A.

EdStainless (Materials) · Answer 1 · 2022-04-10 22:29:07

Give us the rest of the figure titles, including any footnotes.
These are very detailed.
If in doubt contact Battell Columbus, they maintain MMPDS data.

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P.E. Metallurgy, consulting work welcomed

feajob (Aerospace) · Answer 2 · 2022-04-10 23:34:57

Figure 3.7.5.2.8(b):
Product Form = 4.25 to 8.50 inches thick
Specimen Details: Unnotched 0.25 inch diameter
Surface Condition: Polished, final surface finish unspecified
Test Parameters: Loading - Axial, Frequency - 20 Hz, Temperature - RT, Environment - Air
No. of Heat/Lots: Unspecified
Sample Size = 57
Std. Error of Estimate = 0.183
Standard Deviation = 0.814
R^2 = 95%

Figure 3.7.5.2.8(e):
Product Form = 1 to 6 inches thick
Specimen Details: Unnotched 0.25 and 0.30 inch diameter
Surface Condition: Not Specified
Test Parameters: Loading - Axial, Frequency - 800 cpm and unspecified, Temperature - RT, Environment - Air
No. of Heat/Lots: 15
Sample Size = 85
Std. Error of Estimate = 0.507
Standard Deviation = 0.794
R^2 = 59%

EdStainless (Materials) · Answer 3 · 2022-04-11 13:34:23

I took this up in the other thread

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Best fit S/N curves for 7050-T7451