130 deg Flush Head Fastener Metal Joint Allowables

[edbgtr]

G’day Eng-Tippers,

I have a question that a colleague and I are puzzling over.

Does anyone here have a method for correcting 100 degree flush head fastener data in aluminium sheet for other higher angle flush head fasteners? My reverse engineering of the sparse 120 degree data in the MMPDS appears to show a reduction in the head bearing allowable relative to their 100 degree cousins, but not the Briles. It is well known that the 130 degree flush heads are mainly being used in composite joints, but they are also appearing in metallic joints, where there appears to be an acute shortage of joint allowables for higher CSK angle fasteners.

Can anyone here help me on this topic with perhaps a test-based “rule of thumb” correction factor and/or a reference to an approved document or research paper on this subject?

I look forward to your response.

Ed.

 

[WKTaylor]

edbgtr...

What fastener P/N [family?]... or is this a reverse driven [bucked-tail into 130-deg countersink] solid protruding head, such as MS20470?



Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[edbgtr]

Wil..

Thanks for responding.

The fasteners I have encountered, "Hi-lok" types, blinds and secondary structure bolts, have had large airframer fastener codes allocated to them, so I don't know where they originate from. Most are Ti alloy and in the 3/16 to 1/4" dia. range. Where I work, we usually do 100 deg (not 130) double flush installations, when we do use them.

Ed.

 

[WKTaylor]

edbgtr

IF these parts are design/made by a FASTENER manufacturer, then most likely, they will have MMPDS allowables [maybe limited structural alloys/thicknesses, unpublished available on request]. IF NOT, the OEMs could be persuaded to develop those allowables for Your design [IE: for specific structural alloys, thicknesses, etc].

IF these fasteners have been developed by a airframe manufacturer [Boeing, MDC, etc], then getting their proprietary allowables could be like wrestling a bear... don't expect to be victorious with out great pain.

IF these are "spec" fasteners, which have a governing procurement spec [IE: NASMxxxx], then allowables may be deduced... and/or factored [down] by a conservative design factor 1.15 [IE: P= Pf~ X 0.85] for test/use.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[Sparweb]

Edbgtr,
Are you encountering these fasteners in applications where the fastened sheets are too thin for 100 deg CSK (or 120 CSK for that matter)?

I think we've had a few previous go-rounds on the forum here, on the subject of extrapolating test data from one condition to another or interpolating between two test results, when it came to fasteners with no public allowables data. I think we are often stymied in the effort, either by the clamp-up question or the knife-edge problems when the sheets are thin, and that's usually the case driving the question.

When you're done tearing out your hair over that one, you can take a stab at the 156 degree head HL547 .

All of which is to say that, I fear, the only way to crack the nut is to obtain test data, applicable to the joint you're concerned with, much as Will warned.
The alternative may be to arrange for the tests to be done on your behalf $$$$$.

STF

 

[edbgtr]

Sparweb,

Thank you for your words of wisdom regarding this problem. You are quite right regarding my needing some test data for a 130 deg flush head fastener. In the past, I have used known techniques for reverse engineering fastener data to obtain what I need for an application that was not part of a test data set. It was my hope that someone would sanitize a data set for a 130 degree fastener type in sheet metal and offer it to us on this forum to reverse engineer as we see fit for our application. It is a shame that there seems to be less data available now rather than more regarding fastener allowables. Fastener data is being withdrawn from the MMPDS databases rather than it growing as more data becomes available.

So if someone has such data, which can be sanitized to hide its true origin, I would be most grateful. Fastener data that I use in my everyday work covers the shank nominal diameter range from 3/32 through to at least 1/4 or 5/16". In addition, so that a reasonable attempt can be made to reverse engineer the data, the true nominal diameter values per fastener size would be required as well as the head depth (H). The material type, or ultimate shear stress allowable, for the anonymous fastener would be welcome along with the sheet material applicable to the data set.

A data set like this can be used to make very reasonable estimations for other fastener/sheet combinations.

Ed.

 

[edbgtr]

Hi Eng-Tippers

I spent the day trawling the Internet and found an item relating to this topic that was published in the Journal of Aerospace Engineering.

The item is titled, “Influence of Head Geometry on Bolted Joint Behavior”. It appeared in Vol. 15, Issue 4 (October, 2002) of the Journal, pages 136 thru 153.

Ed.

 

[craddojc]

G'day Ed!
I happened across one of your old posts and you mentioned that back then (2003) you did FEM using MSC/Pal (from the good old DOS days). I used MSC/Pal back in the 1990s and recently stumbled onto my old collection of PAL2 model files. Some would be pretty useful to me right now, if I could find a copy of PAL. Any ideas?
thanks very much!
Jeff

 

[edbgtr]

G'day Jeff,

This is a bit O/T for this thread, nevertheless I'm sure the authorities won't mind me answering your question.

If you still have an old DOS machine you'd be able to run the s/w. The new pseudo-DOS will not run PAL. As I recall your machine needed to be free of all other s/w in memory to operate. I've ditched mine, and now use UNA, which is available on the Internet; the 12000 DOF version is free. It has NASTRAN-like problem setup and you can import/export NASTRAN BDFs via the UNA translator. It means building your model "blind" and there's no graphics output either. I started life on NASTRAN v15.5 (1970s) so using UNA is not such a big problem for me. UNA has genuine shear panels and rod elements in its library, like NASTRAN, so checking classical, pure semi-monocoque problems is easy.

UNA has an excellent Manual and a set of example problems to guide you through your first steps at getting it to run.

Dr Zoran Rudic is the owner of the program. His e-mail address, per the Manual, is (una at surf25 dot de). I've not written to him or used this address so don't know if it works. Some of the Internet links for his website seem to be not functioning; not sure why.

I never have understood why the "Big Boys" of FEA s/w don't have free versions of a reasonable model capacity for people to practice on. Most analysts prefer to stay with the s/w they know really well, and having a free version would accomplish more sales for the creators I'm sure.

Ed.

 

[craddojc]

Ed,
thanks very much for the advice- You are a goldmine as always.
I will track down UNA and give it a try
Thanks
Jeff

 

[WKTaylor]

CAUTION. From what I can tell, all 130-deg flush head [and most 120-deg flush head] fasteners are intended almost exclusively for composite structures.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.