## S/N curves for unnotched 7050-T7451 plate

## S/N curves for unnotched 7050-T7451 plate

(OP)

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.

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.

## RE: S/N curves for unnotched 7050-T7451 plate

Different thicknesses? Test conditions? confidence factor?

There are lots of possibilities.

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P.E. Metallurgy, consulting work welcomed

## RE: S/N curves for unnotched 7050-T7451 plate

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%

## RE: S/N curves for unnotched 7050-T7451 plate

800cpm or 13Hz vs 20,000Hz, that is a big difference and is likely the reason for the different values.

The second one is nearly low cycle fatigue.

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P.E. Metallurgy, consulting work welcomed

## RE: S/N curves for unnotched 7050-T7451 plate

## RE: S/N curves for unnotched 7050-T7451 plate

One thing that puzzles me is the large amount of scatter in the second set of data.

That just does not sit right, and would lead to a much lower value in order to have the same level of confidence.

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P.E. Metallurgy, consulting work welcomed

## RE: S/N curves for unnotched 7050-T7451 plate

## RE: S/N curves for unnotched 7050-T7451 plate

Her email is rubaduejatbattelle

This is a dotorg email.

Just don't tell here where you got this

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P.E. Metallurgy, consulting work welcomed

## RE: S/N curves for unnotched 7050-T7451 plate