Fastener Load Distribution
Fastener Load Distribution
(OP)
Where may I find a simple shareware computer program that will "accurately" model the load distribution among fasteners common to joints?
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Fastener Load Distribution
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Fastener Load DistributionFastener Load Distribution(OP)
Where may I find a simple shareware computer program that will "accurately" model the load distribution among fasteners common to joints?
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RE: Fastener Load Distribution
In order to determine the load distribution, a finite element based analysis can be used. The joint is broken down into a series of spring elements. The plates are divided into a number of springs lying between each fastener, which is its self, portrayed as a spring. The spring constant of the plate is a function of cross sectional area and E (Youngs modulous), the spring constant of the fastener (C) is calculated using the NACA document. Once the equations describing deformations of these springs has been derived they can be solved simply in Excel using simple martix inversion methods (which Excel does very well). You don’t need to spend vast sums of dollars and time with expensive FEA software to do this.
The whole point of this exercise is to determine what variation in the plate thickness (spring stiffness) will give an even load distribution. The results of this detailed design and analysis can be seen in joints that are tapered or stepped. Boeing has a manual titled Structural Design for Durability which contains guidance on critical end fastener loads and fatigue resistant joints.
The next stage in the joint analysis is the assessment of the severity factor. This accounts for the effects of the fastener type, method of installation, interference, hole preparation and so on.
Once the severity factor has been determined the fatigue life of the joint can be predicted. This is very important in new designs and also in repair and modification. Fatigue life of repairs and mods can be compared to the original structure, which forms a sound basis for assessing its suitability.
Fastener load distribution is important and can be calculated with relative ease. If anyone would like to know more about this or would like some assistance feel free to contact me.
Nigel Waterhouse
n_a_waterhouse@hotmail.com
A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.
RE: Fastener Load Distribution
Nigel Waterhouse
n_a_waterhouse@hotmail.com
A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.
RE: Fastener Load Distribution
I note that you stated that the stiffness of the fastener could be determined using the NACA reports. I assume that you are referring to NACA TN 1051 (and to its follow up TN 1458).
If so, I have encountered a limitation in this approach that renders it unusable for my requirements. The NACA approach assumes that the bolt will be loaded in a double shear arrangement, with the outer plates carrying equal load.
Beyond this, I have looked at ESDU data sheet 85034, in which its calculations I have little faith. This method can analyse asymmetric cases, but there is an unexplainable discontinuity in its approach, and a double shear case with an outer plate equal to (close to) zero, does not approach a single shear case at all.
Are you aware of any other appraoches that can deal with a variety of materials and assymetric design.
RE: Fastener Load Distribution
RE: Fastener Load Distribution
I am not familiar with the reference you quote. Could you tell me where I can find it, please. Also, I am interested in your problem; sorry I didn't reply to your e-mail. Could you give me a few more details regarding the problem.
Nigel
Nigel Waterhouse
n_a_waterhouse@hotmail.com
A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.
RE: Fastener Load Distribution
Now as a follow up to the original post. My work has involved attempting to write a simple program to calculate the load distribution. It was originally planned as a 4 week task. Now 5 months later, no definitive, acurate, reliable method has been determined to calculate the fastener stiffness. 3 theoretical and 2 empirical methods have been analysed, andnone has been able to be verified. This includes the above NACA TN 1051 method (used in a simplified way in M Niu's "Airframe Structural Design") a couple of propriety methods, and the ESDU method.
None of these methods consider different fastener head properties. Only the ESDU method supports assymetric double shear.
Now for the disturbing aspect. The variation between any of the above methods can be as high as 100%. Using stiffness values that differ by 100& can result in Fastener Loads that differ by up to 50%... obviously resulting in an unreliable application.
As for the Peery/Bruhn suggestion. These do not provide sufficient ingormation to create a generalised calculation methodology, and dot sufficiently allow for differences in fastener stiffness.
RE: Fastener Load Distribution
RE: Fastener Load Distribution
Realize it's a little late but I just read your inquiry.
Try the website: "Design and Analysis of Mechanically Fastened Joints and Bolted Patch Repairs" at
http://www.nrc.ca/iar/bolted_joints_repair.html.
I found that just by going onto Google.
Also the FAA Rapid Assessment and Integrated Design manual at http://www.tc.faa.gov/its/worldpac/techrpt/rapid.pdf
gives load distribution procedures.
Finally, although its dated, you might try "Analytical Design Methods for Aircraft Structural Joints" by McCombs, McQueen, and Perry, AFFDL-TR-67-184
RE: Fastener Load Distribution
http://naca.larc.nasa.gov/reports/1947/naca-tn-1458/
RE: Fastener Load Distribution
RE: Fastener Load Distribution
Thank you
Graham Murphy
RE: Fastener Load Distribution
He can be reached at:
W.F. McCombs
2106 Siesta Dr.
Dallas, TX 75224
He also sells a supplement to the Bruhn textbook which is worthwhile.
Randal Heller
RE: Fastener Load Distribution
I have a copy of the Bruhn "supplement" and it is a very good addition to the basic text.
FYI I finally purchased a copy of the report from NTIS, their No is AD831711.
The report is somewhat dated as it is written pre PC's but there is some interesting data on bolt stiffnesses, and it "filled in some gaps" in my background knowledge.
Rgds
Graham Murphy
Graham Murphy
RE: Fastener Load Distribution
RE: Fastener Load Distribution
Nigel Waterhouse & Associates
Aeronautical Consulting Engineers
Transport Canada and F.A.A approval of fixed and rotor wing aircraft alterations: Structures, Systems, Powerplants and electrical.
n_a_waterhouse@hotmail.com
RE: Fastener Load Distribution
RE: Fastener Load Distribution
RE: Fastener Load Distribution
I don't know of a free or commercial dedicated joint modeller. You tend to find larger companies have in-house methods which have some experimental verification.
[I realise this is way too late to be of use to the original post, but I followed the thread in the hopes of finding more info on free stuff.]
RE: Fastener Load Distribution
Huth, H., The influence of Fastener Flexibility ont he Predictions of Load Transfer and Fatigue Life for Multi-Row Joints," ASTM Conference Presentation
Tate, M.B. Rosenfield, S.J. "Preliminary Investigation on Loads Carried by Individual Bolts in Bolted Joints," NACA TN-1051, Washington, 1946.
Swift, T., "Development of the Fail-Safe Design Features of the DC-10," ASTM STP 486, 1971 pp 164-214.
The were presented in:
Muller, R.P.G. "An Experimental and Analytical Investigation on the Fatigue Behavior of Fuselage Riveted Lap Joints", 1995 Delft University, p 154.