Libris Britannia 4/science library(b).zip/science library(b)/ENGINEER/H477.ZIP/PBS.DOC

Text File | 1990-12-05 | 23KB | 522 lines

                       PBS - Plate Bending Solutions

     General Introduction

     PBS is the COPAN/II module that analyzes LAMCON cross-sections
     for strength and stiffness in pure plate bending configurations.
     The edge fixity is simply supported on all four edges.   The
     plate X-Y dimensions are input by the user and should be limited
     to aspect ratios of less than 5.  PBS handles evenly distributed
     pressures which act normal to the plate surface.

     The laminate to plate orientation may be set to any angle. If an
     angle is not given, then the default value of 0 degrees is used.
     This means the 0 degree axis of the laminate runs parallel to the
     1st side of the plate.

     In addition to bending solutions, PBS Version 1.0 includes a
     buckling routine to produce a edge force density.   This value
     does not refer to face buckling on sandwich structures but rather
     general buckling of an isotropic plate.

     PBS is supplied as a executable COM file although it can be
     called from the ACCESS menu.    To run PBS from DOS, enter BS and
     hit the <CR> key.  (Even though the module name is PBS, we have
     given it the name BS on the disk.)

     PBS is not copy protected.  This is true even on the lower priced
     version which uses a copy-protection scheme.  This means that PBS
     can be used without having a master disk in drive A.  (for those
     of you with the less expensive model)

        A suggestion for floppy disk users

        If  you  will  be using PBS with a single  or  dual  floppy
        system,  or  with  a lap-top machine with 3.5"  drives,  we
        suggest  that  you  set  up a virtural  RAM  disk  for  PBS
        calculations.

        When solving the stiffness matrix, PBS will be reading the
        material file as well as making stratch calculations on
        disk.   To the user, this will be transparent as the
        disk files are erased as soon as PBS is done using them.

        Because of this,  a floppy system may not be desireable due
        to all of the disk spinning that will take place.   Another
        disadvantage  with  the  DC powered lap-tops is that disk
        access draws quite a bit more power from the already small
        reserve.

        A  remedy  to this situation is to set up what is called a
        virtural RAM disk.   With most machines, this can be done
        using a DOS program called VDISK.COM, which is usually
        defined in a CONFIG.SYS file.  eg DEVICE=VDISK.COM *64
     


        The amount of memory that you reserve for the VDISK is
        based on the amount you have available.  However, if
        possible, we suggest at least 64K.   This will give you
        enough room to copy PBS and the .PRP files as well as write
        .OUT  files to it.    A batch file can be created to assist
        with this repetitive task.   If you do not know how to make
        a batch file, check out your DOS manual.

        Now, when you are running calculations, PBS will read and
        write to the virtural disk.   The operations will be
        absolutely quiet and a ton faster.   In addition to saving
        your disk drives from overload, your battery pack will allow
        you a few extra hours of COPANing.


     Starting-Up PBS

     Operating PBS is simple.

     You will load PBS using one of two methods.   Which one you use
     will be determined by how you are using the COPAN/II system.

                             The ACCESS Method

     After ACCESS has been loaded, move the menu pointer to PBS.

     After positioning the pointer to PBS,  hit the <CR>.   The screen
     should  blank out for a few seconds.   The opening screen of PBS
     should then be visible.  If not, read on.


     Troubleshooting the ACCESS System

     For some reason, PBS does not load via ACCESS on all claimed
     compatibles.   Obviously, this is due to some of the subtle
     hardware differences between machines.   It stands to reason that
     if the ACCESS system loaded,  PBS should kick-in with no problem.
     Unfortunately, this is not always the case.   Should the DOS
     prompt appear after your PBS request from ACCESS,  reload ACCESS
     and try it a second time.   Possibly the shell partition was not
     properly reserved on the first attempt.

     NOTE:   If you have been using your machine for other memory
     resident programs, be sure to do a three finger reboot before
     loading ACCESS.

     If after the reboot and reload, ACCESS can still not call PBS, it
     might be safe to assume that your machine is not 100%  comptible
     with COPAN/II.   Not to worry however, you can run PBS directly
     from DOS.
     


                              Running From DOS

     If you are using the ACCESS System,  you need not bother yourself
     with the following instructions.   The exception of course is if
     you were not able to load PBS from ACCESS due to hardware
     incompatiblity problems.

     To load PBS from the DOS prompt, enter BS.  A few examples are
     given:

              A>BS   or   B>BS   or   C>BS   or   C\COPAN>BS

     Be sure to hit the <CR> after you have typed this.


     How to Operate PBS

     Analyzing composite plates for strength and stiffness is quick
     and easy with PBS.   The following is a list of the information
     which you must provide in order for a calculation to occur.

     1.  LAMCON file name
     2.  Plate dimensions
     3.  Fiber Reference Orientation (optional)
     4.  Loading in a uniform pressure


                            Using PBS keywords

     When using PBS, it will be necessary to enter specific keywords
     in order to produce the required prompts.   Each keyword is
     abbreviated with a certain number of leading characters.   For
     example, to exit, you would type EXI.   To load a laminate, you
     would key in LAM.  Upper or lower case is fine.  If you enter too
     many or not enough characters,  PBS will clear the input line and
     redisplay the happy blinker.   As a guide, all keywords are
     displayed on the 25th row of the screen with the necessary
     leading characters in UPPER case.


                          Entering a LAMCON file

     The first order of business is to call in a LAMCON property file.

     When PBS loads, the opening screen will appear.  The screen
     format resembles PCAT and LAMCON in that a rectangular box is
     produced on top of a list of available keywords.   One noteworthy
     difference is that the keywords must be entered manually.   They
     are not assigned to the function keys.
     


     To enter a LAMCON file,  type in the keyword LAM when the happy
     blinker is visible.  This will produce the following prompt.

     Prompt 1 --->      Enter LAMCON / .PRP Laminate:


     PBS is waiting for a the name of an existing LAMCON file.   You
     should not enter the .PRP as only .PRP files can be entered.  PBS
     will attach this file extension for you.  The reason it does not
     say --->  Enter LAMCON file:  is because PBS does not assume that
     the  file  was created with LAMCON.   It is possible for you to
     build and analyze an ASCII .PRP file without using the LAMCON
     module.

     If you decide to cancel without entry, press the <CR> with
     nothing entered.

     After entering a valid LAMCON file name,  PBS will read the file
     and produce a status box in the upper left hand corner of the
     screen.  This box will always be present to remind you which
     laminate file is in memory.   The information in the LAM box is
     the JOB (file name),  the total ply quantity and the overall
     laminate thickness.

     If the file shown in the LAM box is not correct,  you may type in
     LAM again and prompt 1 will be redisplayed.   It is then possible
     to load in a different LAMCON file.   If you have forgotten the
     name of the file,  you will have to exit from PBS using the EXI
     keyword.  The directory may then be reviewed from DOS or from the
     ACCESS program using the [Esc] key function.


                         Defining Plate Dimensions

     The plate thickness will have been predefined based on your
     material selections from LAMCON.  This leaves only the length and
     width to be entered.  The units in which the X-Y values should be
     entered will be displayed just above the happy blinker.

     To activate the necessary prompt,  key in the code,  PLA from the
     happy blinker.  Don't forget the <CR>.

     Prompt 2  --->    Enter Plate Dimensions (### ###)

     Enter the values that you wish your plate to assume.   Keep in
     mind the format required here.  PBS will be expecting both values
     to be entered on the same line separated with one or more blank
     spaces.   If you should press return with only a single value
     entered, or if you forgot the blank space, PBS will let you know.
     


        A PBS Modeling Hint

        When doing a ply-by-ply stress analysis,  keep the plate
        dimensions equal, that is to say, analyze square plates.
        Using aspect ratios other greater than four, with certain
        laminate cross-sections, can sometimes produce "uncertain"
        stress results.

        For this reason, we recommend that you get in a habit of
        using square plates for stress problems.   If you are only
        concerned with laminate bending results, aspect ratios  of
        up to five produce very reliable solutions.  Ratios higher
        than five are accomodated but the theory of plates is being
        stretched a bit (No pun intended) so be careful.


     After the plate dimensions have been entered and accepted by PBS,
     a second status box is displayed just below the LAM box.  The
     information given keeps you abreast of your plate size and the
     orientation of the laminate with respect to the plate side.


                       Modifying the Laminate Angle

     The laminate angle will automatically default to a value of 0
     degrees AFTER the plate dimensions are entered.   This default
     value will be displayed in the PLA status box which is located
     about one third of the way down the left side of the screen.

     To change this 0 to a non-zero, enter the first three characters
     of the keyword ANGLE.  This will produce the following prompt:

     Prompt 3 --->   Laminate angle to first side?

     At this prompt, you should then enter a value between 0 and 90.
     This value will then be displayed in the PLA status box.


        Why Use the Laminate ANGle?

        The ANG feature is used to orient your LAMCON cross-section
        with the plate that you are analyzing.   Remember that the
        section you constructed with LAMCON has no physical
        references with which to align the fibers.   The ANG option
        allows you to define a reference axis.



        Suppose you created a LAMCON file with all fibers running
        at 0 degrees.   Then, in PBS, you defined a plate with X-Y
        dimensions of 40 and 60 inches.   It is obvious that the
        alignment of the unidirectional fibers within the plate
        will have a substantial impact on the plate stiffness.

        If the ANG option is not used when calculating this plate,
        the fibers will be aligned parallel to the short side of
        the plate.    To rotate the orientation so that the fibers
        run  perpendicular to the short side,  a ANG value of 90
        would be entered.

        Consider this example as well.   A LAMCON file is defined
        with a series of 0/90 roving plies.    The file is then
        submitted to PBS to determine the amount of bending under a
        specific pressure.   The same laminate can now be rotated
        45 degrees within the plate to make a direct comparison to
        between the 0/90 orientation and the double bias
        configuration.


                          Entering a Bending Load

     The final requirement for producing PBS results is the load
     entry.  In this version, the load is always an evenly distributed
     pressure acting normal to the plate surface.   A normal force
     vector is perpendicular to the plane of the plate.

     The units in which the pressure should be entered will be
     displayed just above the happy blinker.   They will appear in  a
     reverse video format immediately after the LAMCON file is read.

     To enter a pressure, invoke the prompt with the key code BEN LOA
     It is necessary to have a space between the BEN and the LOA


     Prompt 4 --->     Enter a uniform pressure:


     Any real value will be accepted.  When the entry is complete, PBS
     will display the boundary conditions (simply supported) and the
     pressure that will be applied.

     


                 Submitting the LAMCON File for Processing

     To produce results, the file must now be submitted to PBS for
     processing.   This final task is accomplished with the following
     key code: BEN SOL.  This is an abbreviation for Bending Solution.

     After this command is entered, and if all required input data has
     been supplied,  PBS will respond with a prompt for an output file
     name.  This  is an ASCII file that PBS will use for storing the
     calculation results.  If you do not enter a name, PBS will assume
     that you do not want the output saved on disk.  In this case, all
     output will be routed to the screen; data will not be saved.



                           Quick Printer Summary

        If all that you require is a quick summary, the print-screen
        function  can be used AFTER the results  have  been
        written to the monitor.   A [Ctrl] [PrtSc] will send all
        text to LPT1, which is the primary parallel printer port.

                     More Words About the Output File

     By supplying an output file name, you will be creating a type of
     outbox for all subsequent results.   Each time that you BEN SOL a
     laminate file,  PBS will ask you if you wish to add to the outbox.
     The prompt will appear as:

     Prompt 5 --->   Append output file (Y/N)?

     By pressing the <CR> without a typed response, PBS will assume
     you wish to append the outbox.   Pressing the [N] key and hitting
     the <CR> will suspend output to the file.    On the next
     calculation, the prompt will again appear.  This way, you may be
     selective with the information that is compiled to the outbox.

     With this concept, it is possible to write all information to a
     single report.   Rather than having to "search and collect"  all
     the necessary single output files, one report can be reviewed and
     acted upon.


                          Reviewing Output Files

     The output files created with PBS are formatted  ASCII  files.
     This means that the file on disk is in the same layout as you
     would see on a 80 column sheet of paper.   The data contained by
     any PBS output file can be reviewed with either an editor or via
     a line printer.

     


     (1)  Using a Full Screen Editor

     If you have your own favorite editor such as  WORDSTAR,  open a
     non-document file to review COPAN/II text files.


     (2)  Outputting Text Files to the Printer

     The output files created with PBS can be routed directly to  the
     line printer for hard copy review.   This can be done a number of
     different ways.

     The quick way out is to use the DOS function called PRINT.  The
     major disadvantage with PRINT is that COPAN/II files are not page
     formatted.  This means that a ^L character is not embedded in the
     text which causes the printer to do a form feed.   What you will
     end up with when using PRINT is your output printed across the
     form perforations.   If you must use PRINT,  you could always go
     into the text, and insert some ^L characters.  This would cause
     the printer to page feed at each occurence.   Of course, the
     better way is to use LINER.

     Using LINER to Print Text Files

     A smarter option is using the COPAN/II module called LINER.  This
     is a separate module which has been designed specifically to
     print, fully page formatted, COPAN/II text files.  This program
     can be loaded via ACCESS.    Turn to the section of this
     manual  that addresses the operation of LINER.


                          Summary of a .OUT File

     All of the information that is presented on the video screen is
     also written to the output file.   The disk output file also
     contains a stiffness matrix of equivalent material.   This
     information is available only when a output file is requested.

     Generally speaking, the output file consists of three parts.  The
     first section is the calculation parameters and laminate file
     details such as name, thickness,  x-y dimensions, fiber/plate
     orientation, loading and so on.

     The second section contains the matrix information.  Two matrices
     are given for each laminate cross-section.   The matrices are
     printed for the first calculation.    Then for subsequent
     calculations on the same laminate, the matrix data is not printed
     if the matrix values do not change.    For example, if a laminate
     file is calculated several times with the pressure different on
     each run, the matrix information will be printed only once.  When
     a change is made to the laminate that cause the stiffness matrix
     to be recalculated, the new values will be written.



     The third and final section, of each output report is the bending
     and ply stress data.  A maximum plate displacement is provided
     along with three maximum stress values per ply.

     Maximum plate deflection will occur at the middle of the plate.
     The stress information is defined as Sig-1,  Sig-2 and  SHEAR.
     The short side of the plate is sigma 1 so it follows that the in-
     plane  stresses  for Sig-1 are in  that  direction.   Sigma-2  is
     obviously   the  in-plane  stresses  in  the  direction  of   the
     longitudinal  edge.   SHEAR is a little different than what you
     might expect.

     With normal plate theory,  the subject of shear stress through
     the thickness is given all too little attention.   With
     isotropics, this is no problem,  as shear strength is usually
     high enough to not cause any problems.   This is certainly not
     the case with low to medium density  plastic foam cores.   Rather
     than ignore this,  we have built in a custom routine which
     produces realistic core shear results.   This alogrithm was
     developed using a mainframe finite element processor which
     incorporated a true composite element.  By make multiple runs
     with this system,  we have calculated our own table of
     coefficients for laminated sandwich plates.



     A Word to Our Wise Users

     While we are very pleased with the results,  it is not possible
     for us to say that the calculated shear values will be identical
     to the stress levels that your core may experience within any
     given structure.   We feel obligated to make this statement
     because of the inherent variability of composite constructions.


     The Story of a Sap

     In discussing this, it brings to mind the small story of how a
     finite element processor was given its name.   The program, known
     as SAP, was one of the early mainframe codes that gave engineers
     a real taste for full powered designs.   For many years, users
     referred to the program and, quite unfortunately, the meaning
     behind the name was forgotten.   What took its place was a not so
     clever acronym for Structural Analysis Program.

     The original meaning of SAP was just that, sap.   You know, the
     noun sap, as in without brains, idiot; your basic dumbshit.  It
     was given that name to always remind engineers that computer
     programs, especially the complex ones, are dangerous tools unless
     used by thinking - reasoning - scrutinizing humans.   This one is
     no different.   Never assume that a calculation is anything other
     than just a mathematical approximation.    What you can assume
     quite confidently,  is that error always exists and its your job,
     as the responsible technician, to determine if the amount of
     error is acceptable.
     


                    COPAN/II Plate Bending Benchmark

     In order to verity that PBS is producing reliable results,  a
     benchmark calculation can be run using the following plate
     bending problem:

     Plate dimensions:   78.771" x 78.771"   (2000mm  x  2000mm)

     Thickness       :   .4726"              (12mm)

     Plate Stiffness :   3.04 E+07           (21,000 daN/mm^2)

     Poisson ratio   :   .30

     Uniform Pressure:   .29 lbf/in^2        (200 daN/M^2)

     Edge Fixity     :   Simply Supported


     The  results  obtained  with  COPAN/II  are  compared  with   the
     analytical  solution  for  maximum  deflection as  given  in  the
     Therory of Plates and Shells by S. Timoshenko (Ref 1)


                           Maximum Deflection

                       Theory    COPAN/II    % Error
                       ======    ========    =======
                       .1540"     .1546"      .3896
                      (3.912)    (3.925)


     This benchmark should be used to periodically ensure that PBS is
     producing predictable results with your specific   hardware
     configuration.   If the solution  that your machine produces is
     significantly different from the value given above - you've got a
     problem.

     Note:   A file has been included on one of the COPAN/II diskettes
     which is contains the above properties.   All you will have to do
     is enter the plate dimensions and loading.

     The file name is BENCH.PRP

     REF 1. Timoshenko - Woinowsky - Krieger.
            Theory of Plates and Shells, 2nd Edition, New York 1969