F.D.+E. Calculation Wrappers for SAE Standard Files
member of Fatigue Design & Evaluation Committee of SAE
March 25, 1999, update 2012
Web page: https://fde.uwaterloo.ca/Fde/saewrap1.html
The Fatigue Design and Evaluation Committee of the SAE
with standard file formats for various types of fatigue data. A useful
addition to this process is the creation of calculation, edit and
display capability. The normal computer calculation process usually
requires that one buy or download some files from the internet and then
run the program on one's local computer. Often this entails serious
user interaction with the operating system, and is thus "unsavory" for
many users. It would be much more pleasant to be able to "click" on a
web page button and get the calculation job done by experts or standard
calculation tools.. This is now possible
on many web pages. Generally one uses a web browser to fetch a page
with a "form" to be filled in and a clickable button to send it away
for analysis. The process is still somewhat painful in that one has
to type or cut & paste a local file into the text fields of the
The Quick/Easy Way for Stress-Strain-Life Fatigue Data:
- Open the example file in a web browser:
__________Example Html File___________
- Using your browser edit the file's lines in the text box.
Adjust the "Copyright (C)..." lines to suit your own data.
You must have a value for the elastic modulus in the
NOTE!: Do NOT use TAB to seperate columns. Use 1 or more spaces.
- Use the "Submit" button to view the file's results.
- Use the "Back" button to review and edit. Then re-submit.
- When things work to your satisfaction use the browser
"View Source" option to see the complete file in a
window. Highlight all the text and copy and paste it
into a file on your disk.
- Suggestion: edit the example file in small sections and between
each edit "Submit" the file and view the changes. That way if the
file chrashes out for some reason, it will be easier to determine the cause.
The Calculation Wrapper Process in Detail:
If you have lots of files that you wish to convert to standard
SAE format and to also add calculation wrappers, the above quick
method may become tedious. You may wish to automate the process
by writing a "script" or other program to do the conversions.
Details of such a process are descibed below.
Graphical Explanation 1.1Kb gif
The file is then automatically sent to one of the experimental
- Create standard file(s) on your computer.
In the present case, a standard file implies one of the new SAE/F.D.+E.
standard files for strain-life data, stress-strain data, or rainflow
data. Each has a specific, yet simple, format specified by FD&E or SAE.
The user can either create his own file with any text editor, or in many
cases the data may originate from a testing center or other supplier.
Examples of standard files:
#FileType= strain_life # in the case of strain life files
#FileType= rainflow # in the case of rainflow files
and the line :
#DataType= raw #"raw"= measured, as opposed to "fitted"
Which could be made part of the "standard" SAE file definition?
The two lines simply tell the calculation site what kind of standard
files to expect. At this time the rainflow one does not work
on this site yet.
- The user then places a "Calc Wrapper" around the standard file.
This consists of 5 or 6 lines of text at the top of the file
and 2 lines at the bottom of the file.
The wrapped file is saved back on the user's own disk.
- Wrapper_Head |
- Wrapper_Tail |
Note that the wrapper script will work on a Linux
operating system, but will require alterations to run
- Using a web browser such as Firefox, the user then must
Open File... i.e. open and view the file just created
and placed on your hard drive somewhere.
- Select an option at the top of the page such as "Plot" or
"Calculate" and then click on the Submit button.
(At the moment only Plot works.)
F.D.& E. calculation sites, is plotted or analysed according to
its type and the user option settings, and then returned to the user
for display on his web browser. A simple pre-wrapped
test file is available for
you to try. (You will have to use the scrollbar to read it all.)
Ok, you may have tried this once and yes its cute, but... you might
"How will this help me do my metal fatigue
(or anything else for that matter) job better?
Here are some things to contemplate.
- As long as you place data into the standard format it can be
displayed/ graphed. Thus you can put a lot of things in this
format and still get them graphed ( or analysed, in the future).
- People who do tests for you can send you their results in this
format via email if you wish. If you use your browser for
mail you can "pop" the attached files right there to view
or analyse them.
- You can correct or change the data easily.
Use notepad in Win.. or vi in Linux, or whatever your
favorite editor may be. Beware however that your
editor is set to NOT format the page. In the standard
file there are comment lines and data lines. If the
lines are joined together or "end wrapped" around to make
a new line by your editor, you will have problems. Turn
this feature OFF before you edit.
- Since the head/tail wrapped standard files are also "HTML"
pages, they can be placed in a folder on your local web
server and, voila, you have a database of files (cheap).
You will probably want to add an index page "above" the
standard files, but not much else is required - only the
SAE standard files (text files, mostly).
Our site at the Univ. of Waterloo has a simple file
Using one real data set (plus some
"virtual" sets to demonstrate the layout) we have
created a structure to show how to start your own database.
- If you do not have access to a web server, a simple folder in
your own disk will accomplish the same thing. After you "open"
the first local page from your own machine, like an index, your
browser can find the other pages that the index points to.
Open Page... -> index_file -> file1_fatigue_life.html
Thus even if you don't wish to set this up for other people
you can have your own browsable database.
- In the Head of the wrapper there is an HTML address or URL pointer
which vectors the file contents to a calculation site. Initially
in this case the site is https://fde.uwaterloo.ca/ and the process
it executes there is "catgnume". It is easy to change this site
to some other that you prefer to get the service from. It is also
not terribly difficult for your own web administrator to set this
up on your own server. In fact if you dual load Linux alonside
your MSWindows system, and you then choose a Linux boot,
an APACHE web server is often running, and
it is fairly simple to provide a similar calculation site for
whatever data types you happen to like.
- Security: Because the transportation of your wrapped file data and
the return transport of the results is not presently encrypted, the
data could be "observed" by sites using "packet sniffers". Although
the probability of such acts is fairly low, it is still a possibility
and the user should not transmit any sensitive files in this manner.
If the F.D.&E. folks decide that the whole thing has merit, we may
try to test some encryption methods in the future.
- HTML "pointers" in the data files do not work when they are in a text
field, such as created by the saeheadwrap and the saetailwrap text lines.
The user must click on the submit button and when the file/data returns
the pointers become active and can then be clicked for further files.
- When the plots come back, the directory or folder in Netscape becomes
the same as the address of the calculation/plot handling software.
"Relative" HTML pointers such as: a href="anotherfile.html" will thus
go to the wrong address. It is therefore necessary, presently, to
use the full path in imbedded html pointers. This may be an advantage in
the long run, as it prevents confusion as to where files came from, but
it does make transfer of directory structures across systems more
- The gnuplot utility does a nice job of plotting hysteresis loops, but
the quality of the strain-life plots leave much to be desired. We are
working on getting some better plot routines.
- We are working on getting some data fitting (least squares, etc) routines.
Just for fun, one could ask, "Where could all this lead?". Here is some speculation
on what might be useful (if you think of more, send & we will post them):
- It would be interesting to have a "large" computer facility involved,
such as the one at U. Illinois, to handle large files -filtering RPC road load
files for example. A problem that would arise is the transfer of "large"
RPC files (these days (1999) a large web file is 10Mb), and it would not
be good citizenship to ship a lot of these around the net. A general rule
should be "Keep the files small, and the problems large".
- Many fatigue life computational problems involve "small" input files of
loads or life information and long process times. Simulating the propagation
of a crack through a stress concentratioin zone under variable amplitude loads
can take a long time, particularly if one attempts to do it for a large number
of FEA results, for example. Under such circumstances it might be useful to
ship a standard file to the cgi-bin handling routine of a "broker" machine.
The broker could split the problem into smaller chunks and assign them to
some willing secondary computation machines.
Visual of Concept
The compute load of the calculation machines could be announced to the
broker in some automatic method using similar forms of standard files.
After the individual machines have completed their parts of the solution they
transmit their results back to the broker who collects and returns them to
the client. Such a distribution of the computation would allow one to pose
questions such as: "Give me the life predictions for my Rainflow file
for all 600 materials in
the distributed FDE materials data base" and the means of obtaining a
result fairly quickly.
- If one takes another step and assumes that not only the problem
files, but also the output files from the cgi sites, have a standard
format, one can then "plug" the results into another problem and
repeat the process. Thus we could have a standard "raw" data
strain-life fatigue file that is sent to a cgi calc site, is
reduced and comes back as the common 6 or 7 strain-life fatigue
parameters, or a "fitted" digital curve, and is then sent to
another program that uses it and a rainflow file to
compute life. In a rough analogy one could compare the raw
strain-life file to a "problem-bolt". Our problem-bolt gets sent
to a calc site and returns as a "solution-bolt". In the meantime
a raw time history (problem-nut) is sent to a cgi site and
returns as a rainflow file or
"solution-nut". When they have both returned, along
with possibly a Kt/FEA description ("solution-washer?"), the whole
thing gets re-assembled into a solution-prediction. This might
then be returned to the originator/broker who is assembling a whole
bunch of FEA predictions etc. etc.
As long as a given problem is big enough to warrant the effort,
and decomposible into smaller segments,
the method may be worthwhile. This type of feature may require
inventing some sort of problem identification tag for files, e.g.:
which would require another addition to the standard file description.
How to Proceed?
Can't spoil all the fun. Besides we don't really know if any
of this is worth beans. I guess its a good topic for an
FD&E planning meeting?
Anyone who asks the managerial "When will you have this done"
will have to buy all present a beer.
Page comments to : conle(a)mecheng1*uwaterloo*ca
Last update April 14, 1999.