Hi Sparweb
Yes, lots of folks have made the same mistake and there are some issues with the simplified method too. Along with a friend of mine we teach a 40 hour class twice a year which goes thru the full flight by flight spectrum development process as well as the simple once per flight gag...
Hi
Hate to disagree with anyone here but gag damage being the most significant is just not true. It actually depends on the mission profiles and utilization as well as where on the airframe. For example,actual data shows large transport aircraft like 747, 767, 777, 787, A330, A340, etc have GAG...
Hi Jnnal
There are many papers on spectrum development in the public domain and in particular on the gag cycle, see the ASTMs. Just be very careful about trying to use one equivalent gag cycle to represent the same damage as a full spectrum, This usually does not work. You need to first know the...
Hi
This accident was due to fatigue failure of the anti-rotation lugs. This is one I have covered many times in our DTA course. This was actually missed because the fatigue loads on this part were not representative. The fatigue spectrum did not account for a large number of added cycles which...
You got me, not the best at typing on this particular site using my phone. Obviously, I meant "uses", fingers are too fat ;)
With regards to Bruhn, took me years to get a copy of his missile structures book, its pretty hard to find. It does have a nice reference to a method for developing...
Hi rb1957
Not entirely. The efforts on developing methods for ring analyses goes back even before ww2 and spans the globe. Here are some earlier papers (some easier to find than others):
"A Solution of the Circular Ring", by Roy Miller, May 2, 1931;
"Monocoque Fuselage Circular Ring...
Hi All
Just to add some relevant information. All of the OEM stress manuals I have seen (Boeing, Grumman, Lockheed, McDonnell Douglas, Curtiss Wright, etc.) including both new and old versions, all reference the NACA series of methods for ring frame analysis. The method depends on the time...
Hi ChasGen61
As the other replies you received, yes fuselage structure is allowed to buckle so long as it is not permanent. That being said, on commercial fuselage can tend to happen around 60% of limit. So it can occur at fatigue stresses. Also, pressurization does not entirely prevent...
AliBaig1991
The 2500 hours you quoted in many cases is not atypical of past failures. In fact, many GA aircraft in the past have had wing failures. Here are a few for reference all of which occurred at less than 10,000 hours:
Piper J-3 Cub - 1947 - 566 flight hours
Twin Pioneer - 1957 - 563...
Hi eix
Unfortunately the process is not easy. First of all, there are numerous archives and their search engine is not very good. Once you find the report you are interested in, you can place a request for quote which is limited to a max of 3 documents. Then it takes about 2 to 3 weeks to get a...
Dear eix
It is indeed a great idea to go back and look at past structural analyses. In all my years as a DER, structural reports have progressively gotten worse. Also, much analysis is performed via FEA but many engineers do not correctly validate them as they do not know how to perform the...
Dear ashco
From your diagram, seems like you are modifing tha wing carry thru with an external pod? If yes, this is a big deal. I have worked the 350 on numerous projects as a DER, this is no trivial mod. As the others suggested, you need to find some expert help. In addition to external loads...
If you are trying to use a couple flight tests to extrapolate exceedance data for fatigue spectra, I can tell you, imho, that is a waste of time and will not provide any conclusive data.
There are upwards of 50 or more public references (NASA, DOT/FAA, RAE, DOD, ect) with existing large...
Hi jpaero
If you want to see the changes, you can look at the comet 4 or nimrod structural ipc and srm and compare to the comet 1. There are also RAE papers showing the stress investigations around cutouts.
As for other significant sources, you could always contact The Hub at farnborough and...
Hi jpaero
I concur with the recommendations from LiftDivergence. The process of developing a fatigue spectrum let alone a test spectrum is not a trivial effort particularly if one's aim is to extend the life of the airframe. I have seen several life extension test programs turn into life...
jpaero
Hi, I would recommend looking at and using Hart Smiths codes (a4ej/k). See afwal-tr-81-3154. I find it more useful but thats just preference.
good luck
I believe you will find the curves you are looking for in "Fatigue Data Book: Light Structural Alloys ", 1995 by ASM
If you are looking at a pure theoretical case for a notch in a bar, then I think the reference should give you what you need. However, if you are trying to perform a fatigue...
Hi IBD
Just as a follow up to LiftDivergence, he is right, be very careful with UDRI method. It does not meet 25.571 requirements and can be unconservative depending on the aircraft model and usage. Dr Fawaz and I have presented data on this issue including test results. He and I will be...
