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Official AN bolt material and strength specification
|
| be2
(Mechanical) |
19 Sep
05 9:22 |
Hi, I´m a mechanical engineer with some
knowledge in airplane design. I have a pilots license
and have been involved in some airplane design on an
EAA-basis.
I am now designing a light
biplane two-seater and I´m currently collecting all the
necessary material strength data.
My main
question is: Where do I find official and up to date
AN/MS specifikations for all the ordinary hardware that
you need to design a light airplane.
I
don´t want to specify strength values that I found in
various books or catalogues,though generally I have no
reason to doubt them. I will NOT use data found directly
at Internet sites.
I just want to be official
because my design will be checked by the Swedish
equivalent to the FAA.
One thing I find
especially irritating is that I just can´t find any
official specifikation on the material of ordinary
AN-bolts (AN3 to AN 20).It´s rather important since I´m
going to use a lot of these bolts.
I have the
latest Mil-hdbk (5J) and a wealth of information on
materials from a number of sources (Books, aircraft
material trading companies etc).They all tell me that
AN-bolts are made of 4037 or 8740 steel heat
treated to 125 ksi tension and 75ksi shear. Mil-hdbk has
data on 8740/4140 and Chapter 8, tables 8.1.5.a/b has
information on strengt data for threaded fasteners heat
treated to 125ksi tension and 75 ksi shear. Bruhn and
the old ANC-5 has also strength data on AN-bolts
(bending and combined strengths). Of course I trust
Bruhn and ANC-5 (more or less) but that is strictly not
official strength data.
I have a
specifikation sheet on AN-bolts but it says nothing
about the material, it just specifies the dimensions and
tolerances. I don´t know if the "procurement
specifikation" (Mil-B-6817 I think) says
anything about the material because I can´t find that
spec either.
Can anyone help me with this.I have
no reason to doubt all the strength information I have
gathered from different sources but I just want to get
the official data. I found a specifikation on AN 655
(turnbuckles) but thats all.AC- 4313 has all the info on
steel wires and their specifikations and I´m happy about
that.
To me these are especially important
questions but a lot of people just don´t seem to care
very much.
Would be nice to read some
comments | |
| rb1957
(Aerospace) |
19 Sep
05 10:21 |
|
The actual AN Mil Spec ("BOLT - MACHINE,
AIRCRAFT", AN3 THRU AN20 14 JAN 91) has a table of
strengths. (AN is actually now obsolete, and is
superseded by NASM which has the same table.) The NASM
is published by the AIA:
Aerospace Industries
Association of America, Inc.,
1250 Eye Street,
N.W.
Washington, D.C. 20005.
http://www.aia-aerospace.org/
http://www.aia-aerospace.org/library/library.cfm
For
aerospace standards this website shunts you off to
http://global.ihs.com/?RID=AIA
where
you can buy NASM3-20 and all the other NAS, etc.,
standards for $34 a pop.
It's similar for the
MIL-B-6812 (superseded by NASM6812).
My company
has a deal with IHS so that we access all the common
standards online. It used to be you subscribed and got
hardcopy, then that was superseded by CD-ROM, now it's
via the web. It has never been cheap. How small outfits
get affordable access I don't know (especially a
one-man-band like yourself, be2).
It seems odd
that you've got some sort of spec with the bolt
dimensions but not the strength table. In the AN spec.
the strengths are listed on the last page, page
4.
| |
| wes616
(Aerospace) |
19 Sep
05 13:15 |
I agree with rb1957, use the Assist
website, download the specs (pg 4 of 4 has a strengh
table), and use the table listed on the spec. Even
though the P/N is SS by the NASM, there are plenty on
the market that were made under the old AN p/n.
Wes
C.
| |
Well I'll be, the assist site has the old
AN standards for free.
Handy.
| |
| wes616
(Aerospace) |
19 Sep
05 13:45 |
RP.. that Assist Site is amazing...
this will be my one and only THANK GOD FOR THE
GOVT.
Wes
C.
| |
| be2
(Mechanical) |
20 Sep
05 5:18 |
| Thanks a lot all of You, I think I can
live with the old standards, I already printed and saved
most of what I need them. Its amazing what good advice
there is, if one only asks for
it. | |
be2
1. Sounds like You
need a Boeing, Lockheed, Cessna, etc… liaison handbook,
and/or design manual(s)… which have all the info You are
looking for… and MUCH MORE about aero fastening. Good
luck.
2. If this (1)
is NOT feasible, then I recommend the following basic
documents for starters… most easily procurable thru the
web at say IHS or the FAA AC website. Some may have to
be purchased at nominal cost (of doing business).
MIL-HDBK-5 (old) or MMPDS (current)
metals and fastener data and [any version].
AN3—20 (old) or NASM3—20 (current)
base spec for AN3-X to AN20-X Bolts
Note:
I recommend using newer generation hardware such as
NAS6203—6220 for a number of reasons,
but most importantly higher strength, tighter tolerances
and OVERSIZES are available [for
“aw-sh*ts].
AN960 or NAS1149 for
washers
AN310, AN315, AN316, AN320
[Or equiv NASMxxx], NAS679, etc
Nuts
FF-N-836 or MIL-N-25027
[NASM25027] procurement specs for
Nuts
AS567 Safetying Hardware,
General Practices
MIL-B-6812 (old) or
NASM6812 (current) procurement spec for AN
bolts.
NAS618 standard fastener
dimensions and hole
tolerances
MIL-STD-403C Rivet and
Screw [and low-grade bolt] Installation
spec
AC43.13 for acceptable
maintenance and repair techniques. [FAA
website]
ACs for general maintenance
practices [specifically need procedures for Nut/Bolt
Installation]
3. How does this all
work to insure a fully analyzed Bolted joint
Installation??? As follows..
3.1 MIL-HDBK-5 Para 8.1.5 discusses
how to analyze for “standard bolts” [not shear head,
because reduced fasteners may fail the head in pin
bending when shear-loaded... think-about-it].
3.2 MIL-HDBK-5
Table 8.1.5(a) defines absolute shear
strength of generic “bolts”, based on known [heat treat]
shear-stress capability. ANXX bolts are roughly 75-KSI
and NAS62XX Bolts are 95-KSI [approx values ONLY]. NOTE:
the NASM3—20 spec actually provides max rated strength
for each bolt size. Example form this table for a
0.250-In diameter 75-KSI shear bolt:
P
(shear-ult) = 3680-lbs
3.3 MIL-HDBK-5
Table 8.1.5.1. Unit Bearing Strength of Sheet and Plate
in Joints With Threaded Fasteners or Pins; Fbru = 100
KSI. This defines bearing-tear-out for
“generic 100-KSI material [try finding it]. The intent
is to match fastener [hole] diameter and sheet thickness
to determine a “shear ultimate”… based on 100-KSI
material. This number is then factored up/down based on
the FBru of the “real-world” alloy being analyzed.
Example [MIL-HDBK-5J, Table 8.1.5.1]:
0.250-In
Dia Hole thru 0.10-thick material (at 100-KSI Fbru) =
2500-lbs bearing force.
For 7075-T6 sheet,
0.10-thick, 2-D edge distance, from table 3.7.6.0(b1),
Fbru (A) = 156-KSI.
Therefore max allowable
bearing load for this sheet metal is 156/100 x 2500-lbs
= 1.56 x 2500 =
3900-lbs
3.3 Comparing
shear ultimate VS material Bearing ultimate determines
MAX allowed P (shear) at this location. Example [for the
0.250-dia bolt in 0.100-thick sheet]:
Bolt Shear
Ult = 3680-lbs
Hole Bearing Ult =
3900-lbs
Therefore, Ult allowable load at this
hole is the lesser of these loads = 3680-lbs [bolt fails
slightly before the hole fully-tears-out, not a bad
joint if I do say-so].
Note: this analysis
presumes a "standard head bolt" with a shear-rated nut
[W/WO a washer].
Regards, Wil
Taylor | |
| be2
(Mechanical) |
21 Sep
05 5:54 |
Hi,Wil, thanks for Your
comments.
I have the Mil-hdk 5-J, AC 43-13 and a
number of fairly up to date hardware specifikations that
I recently downloaded . It´s very nice that someone
takes the inconvenience to diskuss the analyze of a bolt
fitting.
I work as a consultant mechanical
design engineer, doing various small CAD-engineered
projekts in that field (currently designing a horrible
smelling food-waste pump for restaurants). So I´m
supposed to do stress calculations now and then, but it
seldom happens. I am very interested though in airplane
stress calculations and think I have a fairly good idea
what it´s all about. That´s why I´m a stickler about
specifikations and getting the numbers
right.
In my little private project I try
to run it as a professional would do, from two reasons:
In the long run it will help me to get my design cleared
without discussions (and redesign) and I myself will
feel a lot more confident at the time of getting the
thing off the ground.
About bolted joints:
I have a lot of information from Bruhn etc (lug
analysis, multiple bolt joints etc) and I think it makes
sense to try to analyze my fittings using various
assumptions. I will also separately stress test all
fittings that I´m unsure of,and that´s a good practice
when it comes to FEA analyzed fittings too, besides
testing the whole airplane.
So, thanks Wil, for
running the example from the Mil-hdbk, it´s very
reassuring for me that I understand what You´re talking
about since I don´t have contacts with any real
knowledge in airplane design, that I can share my ideas
with.
I don´t know if it´s necesarry to use
high strength bolts except in a few areas. Many of my
fittings will be bolted to wooden mebers (I have a copy
of ANC-18 and -19) and I guess its wooden bearing
strength that is often critical there. The reasons You
give for using higher strength (and oversize) bolts are
however very well worth of considering. I hadn´t thought
of the {aw-sh*ts}until now.
As for sheet material
it will be mainly 4130N since I think it will be the
easiest and cheapest to find. I don´t think I will try
to trade sheet thickness for high strength (buckling
considerations) except maybe if I really gain something
with it.
/Anders
| |
| rb1957
(Aerospace) |
21 Sep
05 9:42 |
be2,
4130N maybe be cheap, but the
resulting design will be heavy. i would have
thought that if you could get 4130N, then you could get
4130 "1/4hard" (125ksi). possibly buy the
annealled condition, then heat treat (possibly after
forming) ... shouldn't distort too much
good luck
with your
project | |
| be2
(Mechanical) |
22 Sep
05 10:40 |
| Thanks, I need all he luck I can get.I
try to keep it as simple and cheap as possible, and I
will keep radiuses gentle and large so I won´t have to
stress releive the
fitings. | | |
|
|
| |
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