Bearing bypass stress in skin with countersunk fasteners

[philwi]

I would like to know how to analyze countersunk fasteners through composite skin subjected to both bearing and by-pass stresses. The composite skin is structural and carries considerable load in compression in shear, with a large quantity of fasteners introducing additional compression into the panel through bearing. I know the Interactive Composite Bolted Joint Stress Field Model (BJSFM) is intended for such a condition, but lacks any factors for countersinks. Any help is greatly appreciated, thanks.

 

[Klompder]

Philwi,
The factor for the countersink is incorporated in the test coupon configuration by using the applicable CSK fasteners. Normally the joint bearing stress allowable "p" is derived from the results of the test specimen configuration(s) by application of statistical and other procedures on the test data.

 

[RPstress]

Is the BJSFM the one described in this report from 1981?:

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA101659&Location=U2&doc=GetTRDoc.pdf

http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA101659

 

[fbdandloadpath]

Rpstress,

Yes, that's the BJSFM referred to. The key to the use of BJSFM is the correlation of the analytical predictions possible with BJSFM to reality. The DIST parameter (some call it Rc) is what is used to adjust the analytical predictions to match test data.

First get statistically determined materials properties from lamina test specimens using the material system and specimens made in your facility. Set up a laminate test program with both open holes (countersunk and non-countersunk), and loaded holes (counetrsunk and non-countersunk). Run the tests to failure. Use BJSFM to determine the correct DIST parameter to match your test results. Be ready to determine various DIST parameters for different material conditions (hot, cold, wet, etc.). Once you have derived approprate DIST factors, you are ready to use BJSFM as an analytical tool to predict states of strain and to predict laminate failure. Use of BJSFM without the above is not "real". An efort such as the above could take ~6 months to accomplish.

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