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Stress Calculations

thread828-240633

Stress Calculations

Stress Calculations

(OP)
Hi, I am very new to Mechanica. I am trying to do a simple stress calculation on a cantilevered beam, so that I can verify the stress calculations that Mechanica does, with my hand calcs. The beam is a 1in*1in*100in beam.

I have constrained the back face of the beam so there is no rotation nor translation in any of the three possible directions, and on the furthest face (the tip), i have a force (300in*lbm/s^2) along the top edge going downwards.

The stress calculations seem to very from my hand calcs by as much as 32%.

My calcs max stress = 180,000 lbm*in/in^2*s

Mechanica: max_stress_prin = 2.214994e5
Max_stress_zz=-2.37e5

Does anyone know what threads i can look in for more information on this, or what could be wrong? Thanks.

RE: Stress Calculations

(OP)
This is what mechanica outputs to me.





------------------------------------------------------------
Mechanica Structure Version K-03-39:spg
Summary for Design Study "MyAnalysis"
Fri Mar 20, 2009   14:32:29
------------------------------------------------------------

Run Settings
   Memory allocation for block solver: 128.0     

Parallel Processing Status
   Parallel task limit for current run:            4
   Parallel task limit for current platform:      64
   Number of processors detected automatically:    4
Checking the model before creating elements...
These checks take into account the fact that AutoGEM will
automatically create elements in volumes with material
properties, on surfaces with shell properties, and on curves
with beam section properties.

   Generate elements automatically.
Checking the model after creating elements...

Excluded elements may be required near one or more
loads due to concentrated stresses.
No errors were found in the model.

Mechanica Structure Model Summary

   Principal System of Units: Inch lbm Second (Pro/E Default)

   Length:          in
   Mass:            lbm
   Time:            sec
   Temperature:     F

   Model Type: Three Dimensional

   Points:                 12
   Edges:                  33
   Faces:                  34

   Springs:                 0
   Masses:                  0
   Beams:                   0
   Shells:                  0
   Solids:                 12

   Elements:               12

------------------------------------------------------------

Standard Design Study

Analyses:
   MyAnalysis
   static_mpa

Analysis MyAnalysis requires input data from
analysis static_mpa.

Static Analysis "static_mpa":

   Convergence Method: Single-Pass Adaptive
   Plotting Grid:      4

   Convergence Loop Log:                         (14:32:30)

   >> Pass  1 <<
         Calculating Element Equations           (14:32:30)
            Total Number of Equations:     288
            Maximum Edge Order:              3
         Solving Equations                       (14:32:30)
         Post-Processing Solution                (14:32:30)
         Checking Convergence                    (14:32:30)
         Resource Check                          (14:32:30)
            Elapsed Time     (sec):       0.73
            CPU Time         (sec):       0.45
            Memory Usage      (kb):     180156
            Wrk Dir Dsk Usage (kb):          0

   >> Pass  2 <<
         Calculating Element Equations           (14:32:30)
            Total Number of Equations:     567
            Maximum Edge Order:              5
         Solving Equations                       (14:32:30)
         Post-Processing Solution                (14:32:30)
         Checking Convergence                    (14:32:30)
         Calculating Disp and Stress Results     (14:32:30)

         RMS Stress Error Estimates:

         Load Set          Stress Error  % of Max Prin Str
         ----------------  ------------  -----------------
         MyLoadSet          3.20e+03       1.3% of  2.37e+05

         Resource Check                          (14:32:30)
            Elapsed Time     (sec):       0.95
            CPU Time         (sec):       0.58
            Memory Usage      (kb):     182260
            Wrk Dir Dsk Usage (kb):          0

   Total Mass of Model:  9.791206e+00

   Total Cost of Model:  0.000000e+00

   Mass Moments of Inertia about WCS Origin:

     Ixx:  3.26382e+04
     Ixy: -7.11237e-17  Iyy:  3.26382e+04
     Ixz: -6.21725e-15  Iyz:  7.10543e-15  Izz:  1.63187e+00

   Principal MMOI and Principal Axes Relative to WCS Origin:

            Max Prin           Mid Prin           Min Prin
           3.26382e+04        3.26382e+04        1.63187e+00

   WCS X:  0.00000e+00        1.00000e+00        0.00000e+00
   WCS Y:  1.00000e+00        0.00000e+00        0.00000e+00
   WCS Z:  0.00000e+00        0.00000e+00        1.00000e+00

   Center of Mass Location Relative to WCS Origin:
                  (-3.54343e-18, -2.26780e-17,  5.00000e+01)

   Mass Moments of Inertia about the Center of Mass:

     Ixx:  8.16015e+03
     Ixy: -7.11237e-17  Iyy:  8.16015e+03
     Ixz: -7.95197e-15  Iyz: -3.99680e-15  Izz:  1.63187e+00

   Principal MMOI and Principal Axes Relative to COM:

            Max Prin           Mid Prin           Min Prin
           8.16015e+03        8.16015e+03        1.63187e+00

   WCS X:  0.00000e+00        1.00000e+00        0.00000e+00
   WCS Y:  1.00000e+00        0.00000e+00        0.00000e+00
   WCS Z:  0.00000e+00        0.00000e+00        1.00000e+00

   Constraint Set: MyConstraintSet

   Load Set: MyLoadSet

      Resultant Load on Model:
         in global X direction: -7.083754e-06
         in global Y direction: -3.000000e+02
         in global Z direction: -7.049525e-09

      Measures:

      max_beam_bending:   0.000000e+00
      max_beam_tensile:   0.000000e+00
      max_beam_torsion:   0.000000e+00
      max_beam_total:     0.000000e+00
      max_disp_mag:       3.028639e-01
      max_disp_x:         2.798528e-05
      max_disp_y:        -3.028552e-01
      max_disp_z:         2.292079e-03
      max_prin_mag:       2.371181e+05
      max_rot_mag:        0.000000e+00
      max_rot_x:          0.000000e+00
      max_rot_y:          0.000000e+00
      max_rot_z:          0.000000e+00
      max_stress_prin:    2.371181e+05
      max_stress_vm:      1.650229e+05
      max_stress_xx:      1.098862e+05
      max_stress_xy:     -7.696971e+03
      max_stress_xz:     -2.665295e+03
      max_stress_yy:      1.045842e+05
      max_stress_yz:      2.954562e+03
      max_stress_zz:      2.370292e+05
      min_stress_prin:   -2.214972e+05
      strain_energy:      4.542822e+01

Analysis "static_mpa" Completed  (14:32:30)

Buckling Analysis "MyAnalysis":

   Convergence Method: Single-Pass Adaptive
   Plotting Grid:      4

   Convergence Loop Log:                         (14:32:30)

   >> Pass  1 <<
         Calculating Element Equations           (14:32:30)
            Total Number of Equations:     288
            Maximum Edge Order:              3
         Solving Equations                       (14:32:30)
         Post-Processing Solution                (14:32:30)
         Checking Convergence                    (14:32:30)
         Resource Check                          (14:32:30)
            Elapsed Time     (sec):       1.25
            CPU Time         (sec):       0.73
            Memory Usage      (kb):     187316
            Wrk Dir Dsk Usage (kb):          0

   >> Pass  2 <<
         Calculating Element Equations           (14:32:30)
            Total Number of Equations:     381
            Maximum Edge Order:              4
         Solving Equations                       (14:32:30)
         Post-Processing Solution                (14:32:30)
         Checking Convergence                    (14:32:30)
         Calculating Disp and Stress Results     (14:32:31)

         RMS Stress Error Estimates:

         Mode   Stress Error  (% of Max Modal Stress)
         ----  --------------
            1      19.6%

         Resource Check                          (14:32:31)
            Elapsed Time     (sec):       1.49
            CPU Time         (sec):       0.86
            Memory Usage      (kb):     188404
            Wrk Dir Dsk Usage (kb):          0

   Total Mass of Model:  9.791206e+00

   Total Cost of Model:  0.000000e+00

   Mass Moments of Inertia about WCS Origin:

     Ixx:  3.26382e+04
     Ixy: -7.11237e-17  Iyy:  3.26382e+04
     Ixz: -6.21725e-15  Iyz:  7.10543e-15  Izz:  1.63187e+00

   Principal MMOI and Principal Axes Relative to WCS Origin:

            Max Prin           Mid Prin           Min Prin
           3.26382e+04        3.26382e+04        1.63187e+00

   WCS X:  0.00000e+00        1.00000e+00        0.00000e+00
   WCS Y:  1.00000e+00        0.00000e+00        0.00000e+00
   WCS Z:  0.00000e+00        0.00000e+00        1.00000e+00

   Center of Mass Location Relative to WCS Origin:
                  (-3.54343e-18, -2.26780e-17,  5.00000e+01)

   Mass Moments of Inertia about the Center of Mass:

     Ixx:  8.16015e+03
     Ixy: -7.11237e-17  Iyy:  8.16015e+03
     Ixz: -7.95197e-15  Iyz: -3.99680e-15  Izz:  1.63187e+00

   Principal MMOI and Principal Axes Relative to COM:

            Max Prin           Mid Prin           Min Prin
           8.16015e+03        8.16015e+03        1.63187e+00

   WCS X:  0.00000e+00        1.00000e+00        0.00000e+00
   WCS Y:  1.00000e+00        0.00000e+00        0.00000e+00
   WCS Z:  0.00000e+00        0.00000e+00        1.00000e+00

   Previous Static Analysis: static_mpa
   Load Set: MyLoadSet

   Constraint Set: MyConstraintSet

   Number of Modes: 1

      Mode    B. L. F.    
      ----  ------------  
         1  1.151762e+02

Analysis "MyAnalysis" Completed  (14:32:31)

------------------------------------------------------------

Memory and Disk Usage:

   Machine Type: Windows NT/x86
   RAM Allocation for Solver (megabytes): 128.0

   Total Elapsed Time (seconds): 1.54      
   Total CPU Time     (seconds): 0.89      
   Maximum Memory Usage (kilobytes): 188404    
   Working Directory Disk Usage (kilobytes): 0         

   Results Directory Size (kilobytes):
   460 .\MyAnalysis

------------------------------------------------------------
Run Completed
Fri Mar 20, 2009   14:32:31
------------------------------------------------------------
 

RE: Stress Calculations

Hi rentien

Well first how are you doing your hand calculations for stress?  Are you calculating the Von Mises stress, because this will take in consideration of all of the principal stress and max shear and this is what you see in your plot?  

 

Tobalcane
"If you avoid failure, you also avoid success."  

RE: Stress Calculations

Oh, also you should do your ProM in units of Inch Pound Seconds instead of Inch Mass Secounds, makes life easier.

Tobalcane
"If you avoid failure, you also avoid success."  

RE: Stress Calculations

Hi Mohan,

Are you using ProM? And it would be a good idea to start your own thread on this topic.

Tobalcane
"If you avoid failure, you also avoid success."  

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