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eBJSFM © - Technical Documentation

© 2010 ESP Composites, LLC of 4

eBJSFM © is an Excel based pre and post processor to the public domain Fortran code

BJSFM (Bolted Joint Stress Field Model) [1]. The full field stresses and strains for bearing and

bypass loads are calculated. The max strain and max stress failure criteria are calculated at the

“characteristic dimension”, d0, to determine failure.

θ

x

y

W

D

d0

Pbr

Nx Nx

Ny

Ny

Nxy

Nxy

θ

x

y

W

D

d0

Pbr

Nx Nx

Ny

Ny

Nxy

Nxy



1.0 Bearing and Bypass Solution

The bypass solution is computed as open hole, using Lekhnitskii’s [2] solution. A finite width

correction factor is not applied to the bypass solution. The bearing solution is then computed via

Fourier series and DeJong’s [3] solution for finite width. These two solutions are combined to

generate the full field stresses and strains.

The bearing solution in BJSFM assumes the bearing load is reacted in tension. However, this is

not the only way to react bearing loads. Bearing loads may be reacted in compression, shear, or

any combination of these. The eBolt program, developed by ESP Composites, LLC provides a

solutions that reacts the bearing load in any desired direction.



2.0 BJSFM Fortran Code

If failure criteria are requested from eBJSFM.exe, the results are not accurate or reliable.

However, the raw laminate stresses and strains and lamina stresses and strains were found to be

accurate and reliable. eBJSFM collects only the laminate stresses and strains from eBJSFM.exe.

Within the Excel spreadsheet, the lamina (layer) stresses and strains are then transformed into

their respective 1-2 systems and the maximum stress and maximum strain failure criteria are

calculated. This approach was found to give accurate results.

3.0 eBJSFM Hard Coded Variables and Output

eBJSFM calculations occur at every 5 degrees from 0 to 360 degrees around the hole and this

cannot be changed. This is minimum that BJSFM will allow for without modification.

eBJSFM.exe inputs are bypass stresses and bearing stress. Since the more common input

method is to use bypass running loads and bearing loads, these modifications are computed

internally in the Excel spreadsheet.

The “input.txt” and “output.txt” files are coded to have a set number of input and return lines.

Therefore, all 8 layer directions are automatically analyzed. If the layer is not used in the

analysis, a dummy layer is used, with a return value of 9.99 degrees in the “output.txt”. This is

filtered out in the Excel file and therefore 9.99 degrees can not be used an actual input to

eBJSFM. The dummy layers are give a thickness of 0.00000001”, which does not have a

significant effect to the result. In the event that the Excel bearing load input is 0.0, a dummy

value of 0.00000001 lb is used, which does not have a significant affect to the solution.



4.0 References

[1] Garbo, S.P., and Ogonowski, J.M., "Effects of Variances and Manufacturing Tolerances on

the Design Strength and Life of Mechanically Fastened Composite Joints," Vol 1, 2 and 3,

AFWAL-TR-81-3041, April 1981.

[2] Lekhnitskii, S.G., Anisotropic Plates, Gordon and Breach, New York, (1968).

[3] DeJong, “Stresses Around Pin-Loaded Holes in Elastically Orthotropic or Isotropic Plates”,

Journal of Composite Materials, Volume 11, July 1977, p.313-331

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