7075 vs 7068 Fatigue Data 1

[BrainFailure]

I have always wondered if 7068 would perform better at high cycle fatigue, but until recently I could not find any information. Here is what I found:

http://www.kaiseraluminum.com/wp-content/themes/kac/files/alloy-7068-rod-and-bar.pdf

The only problem is that this test had a static stress concentration factor of Kt = 1.6

1)Does anybody have a 7075 curve with Kt = 1.6 for comparison?

2)Is there a way to estimate how 7068 would perform with Kt = 1?

3)Are the stresses that are plotted already adjusted for the static stress concentration factor or are the stressed plotted just the cyclic max of the average stress over the stress area?

 

[TVP]

DOT/FAA/AR-MMPDS-01 Metallic Materials Properties Development & Standardization has a curve of 7075 with Kt = 1.6. This was the replacement for MIL-HDBK-5, and has now been updated to at least the -04 level. The exact location is page 3-407, Figure 3.7.6.1.8(b). Best-fit S/N curve for notched, Kt = 1.6, 7075-T6 aluminum alloy rolled bar, longitudinal direction.

If you do not have access to this standard, and cannot afford to purchase it, you may be able to find it at a university library. For what it's worth, the fatigue data for the two alloys are similar, with perhaps a small improvement at high cycles for 7068. For example, under fully reversed conditions (R = -1), a 20 ksi maximum stress for 7068 results in around 1.5 million cycles or thereabouts. For 7075, a 20 ksi max stress would result in around 200,000 cycles. Not sure if the Kaiser data has been accepted as statistically valid for acceptance to MMPDS...

 

[BrainFailure]

Thanks TVP!!

$600 is quite a steep price. Probly worth it but I know I couldn't convince my boss.