A-286 RT Fatigue Data

[edbgtr]

Hello All

I'm looking for RT fatigue S-N data for the high strength Cres material A-286, now widely used in aircraft bolts. Only high temperature S-N data is available in the MMPDS-02 and I'm searching for normal operating temperature data relating to the 170 ksi Heat Treat condition.

Curves with log-functions similar to those in the MMPDS will be helpful or p=0.5 Weibull curves if they are available. Any R value will do if only a single stress ratio is available.

There is a shortage of supply in certain high strength bolts and fasteners at present and I'm looking to get approval for possible viable alternatives.

Can anyone help? Any assistance will be much appreciated.

Thanks.

Ed

 

[TVP]

The best source of this type of data would be one of the aerospace fastener producers like SPS, Alcoa (Fairchild), etc. There is one figure showing RT S-N curves for A-286 in the following document (Figure 8.61 on page 80):

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720022813_1972022813.pdf

 

[tbuelna]

edbgtr,

although recently obsoleted, MIL-HDBK-5 gives RT S-N properties for AMS 5737 (A-286 sol. HT & aged to 140ksi uts). I've not normally seen it used as a fastener material at higher strengths than that. If a higher strength material (ie. 180ksi)is needed, AMS 5663 (Inconel 718) is normally used.

A-286 is an iron based alloy and Inconel 718 is a nickel based alloy. Since all of the hybrid cars are now using NiMH batteries, maybe that's why you're having trouble getting nickel alloy fasteners. And what you're experiencing is not uncommon. There is currently a shortage worldwide of many types of high performance steel alloys. The guys that manufacture landing gear are especially hurting:

http://www.nxtbook.com/nxtbooks/mh/mroshownews041707/index.php?startpage=14

Of course, I'm sure there are also unscrupulous parties (or maybe astute businessmen, depending on your viewpoint) that have seen this shortage coming and have bought up and stockpiled these alloys to turn around and sell at a handsome profit.

I used to work for a company that machined a lot of specialized parts in a very high strength alloy, C300. C300 was a proprietary alloy produced in very limited quantities. The owner of the company bought every piece of C300 he could get his hands on and socked it away. When one of these specialized parts needed to be made, either he got the job, or if one of his competitors got the job they had to buy the material from him, at an inflated price.

 

[edbgtr]

TVP, tbuelna
Thank you very much for your input it is much appreciated. The delay in responding to you allowed me to successfully complete the substantiation. Although I wasn’t able to use your suggestions directly, it did help to build confidence in the meagre data I had.
Using bolt manufacturer information and the NAS bolt quality standards, I was able to build enough confidence in what data I had to substantiate the static and fatigue qualities of the alternate bolt. This, coupled with the original joint design work, which was thankfully conservative, allowed me some latitude to clear the alternate bolt for use in the application. The bolt and sleeve design provided a good platform from which to assess the intact fatigue life using the elevated temperature MMPDS data. The good crack growth properties of this tough material took care of the failsafe DT life needed. The MMPDS elevated temperature static strength properties associated with the fatigue data, when corrected for temperature, line up with the minimum RT properties of the alloy, so I was happy that the test material was in the same temper condition as the alternate bolt.
As this alloy is appearing more and more in RT fastener applications, it would be useful if more RT fatigue test data was to appear in the public domain.
Ed