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7050 Plate Lug Curves 3
- Thread starter bf109g
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Hi Gustav
From a reliable in-house source I have compared Ftu/Fty ratios and ultimate strain values for 7050-T7451 plate with 7050-T736 die forgings. For L-grain parallel with the axial direction of the lug, the ratios are similar i.e. circa 1.17 and max strain is 6 percent. For the forging material they use a Ktu vs W/D curve that has the following W/D vs Ktu coordinates; (1.5;0.94), (2.5;0.86), (3.5;0.73), (4.5;0.64). Fit a smooth curve through these points. This curve is also used for 2618-T651 rolled or machined plate less than 3.25 inches thick.
As a first pass design sizing exercise, a fitting factor could be applied and maintain a positive static margin on top of that so that you can address manufacturing concessions and in-service repairs if your component cannot be easily replaced.
The use of FTI bushes claim to improve the fatigue life, but static and fatigue strength should be proven by test.
I hope this helps.
Ed.
From a reliable in-house source I have compared Ftu/Fty ratios and ultimate strain values for 7050-T7451 plate with 7050-T736 die forgings. For L-grain parallel with the axial direction of the lug, the ratios are similar i.e. circa 1.17 and max strain is 6 percent. For the forging material they use a Ktu vs W/D curve that has the following W/D vs Ktu coordinates; (1.5;0.94), (2.5;0.86), (3.5;0.73), (4.5;0.64). Fit a smooth curve through these points. This curve is also used for 2618-T651 rolled or machined plate less than 3.25 inches thick.
As a first pass design sizing exercise, a fitting factor could be applied and maintain a positive static margin on top of that so that you can address manufacturing concessions and in-service repairs if your component cannot be easily replaced.
The use of FTI bushes claim to improve the fatigue life, but static and fatigue strength should be proven by test.
I hope this helps.
Ed.
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Gustav
My apologies for the delay, but my data from different sources for aluminum alloys is not consistent. This appears to be due to in-house test results yielding different Ktru and Ktry values for plots similar to those given in Bruhn Fig D1.15. This alternate source groups ALL aluminum alloys under a single curve for Ktru and another for Ktry. Their Ktry curve is more optimistic than Curve 3 of D1.15.
Where I am working now, an in-house lug analysis tool (computer program) suggests using Curve 6 for Ktru and Curve 3 for Ktry from Fig D1.15 with 7050-T7451 plate.
It should be noted that the Kt-factors in the Bruhn lug analysis are referred to stress concentrations, which is not totally true. The allowable loads increase with increase in Kt, which somehow doesn't quite make sense. The inverse should be true.
Ed
My apologies for the delay, but my data from different sources for aluminum alloys is not consistent. This appears to be due to in-house test results yielding different Ktru and Ktry values for plots similar to those given in Bruhn Fig D1.15. This alternate source groups ALL aluminum alloys under a single curve for Ktru and another for Ktry. Their Ktry curve is more optimistic than Curve 3 of D1.15.
Where I am working now, an in-house lug analysis tool (computer program) suggests using Curve 6 for Ktru and Curve 3 for Ktry from Fig D1.15 with 7050-T7451 plate.
It should be noted that the Kt-factors in the Bruhn lug analysis are referred to stress concentrations, which is not totally true. The allowable loads increase with increase in Kt, which somehow doesn't quite make sense. The inverse should be true.
Ed
bf109g,
I ran into a similar problem. There is a Boeing document which covers these materials, although the document is proprietary. I only mention it as I do not know whom you work for.
The alternative is to use the cutoff curves for aluminum alloys, thus ensuring you are as conservative as possible. You could then make an arguement that the 1.15 Fitting Factor would not need to be applied as the data is validated by test (this is a strech, but maybe worth a try).
jetmaker
I ran into a similar problem. There is a Boeing document which covers these materials, although the document is proprietary. I only mention it as I do not know whom you work for.
The alternative is to use the cutoff curves for aluminum alloys, thus ensuring you are as conservative as possible. You could then make an arguement that the 1.15 Fitting Factor would not need to be applied as the data is validated by test (this is a strech, but maybe worth a try).
jetmaker
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strWennie1
Aerospace
I highly recommend you using the AFFDL-TR-69-42 lug method. I believe that the grumman manual also assessed lugs with this methodology.
I know the OEM's put strict limits on ratio ranges- more restrictive than bruhn. Many times the test lab will do a few points and say use xx curve valid for W/d range XX.
I know the OEM's put strict limits on ratio ranges- more restrictive than bruhn. Many times the test lab will do a few points and say use xx curve valid for W/d range XX.
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