Learning Forum

[Matthew Pirkle]

I am trying to model composite damage in a flat plate (fixed at one end with applied displacement on the other; basically a tension test) with a central hole using progressive damage analysis via the CDM method with the Hashin failure criteria. The layup is quasi-isotropic: [0_3/(+-45)_3/90_3]S. The type of element used is SHELL281. I am able to get the nonlinear solution to converge, but do not know what the displayed results mean.

When I view the results using PLNSOL,PDMG,MT, what do the numbers represent on the color scale at the bottom of the screen? Are these the failure index, I, for the Hashin Criterion? In effect, am I really just plotting a nodal contour of the failure index?

From my understanding, if these numbers are indeed the failure index, any value above 1 would indicate that failure is predicted to occur for the particular failure mode (MT, MC, FT, or FC) in the particular lamina displayed. In my case, I am seeing results for the various layers and failure modes, but the values in the color scale at the bottom of the screen never exceed 1, which would lead me to believe that none of the laminas will experience failure. The results are displayed in the 1.0 true scale setting in the displacement window options. Please see attached.

I am trying to increase the amount of applied displacement in order to see if I can get the numbers in the color scale to exceed 1, but I am unable to apply more than 0.8 mm of displacement, as the solution will no longer converge due to highly distorted element and nodal displacement warnings. I have increased the number of substeps from 100 to 200, and increased the allowed nodal displacement to 1000000000000, but still encounter distorted element errors. Is it possible I need to perform local mesh refinement? The displacement is applied over 8 load steps at 0.1 mm per load step.

Here is a chunk of the code:

/SOLU                                                   !ENTER THE SOLUTION MODULE

/NERR,,,-1                                           !SUPPRESS ERROR MESSAGES

ANTYPE,STATIC                                 !SET STATIC ANALYSIS

NLGEOM,ON                                     !TURN NONLINEAR GEOMETRY ON

TIME,1                                                  !SET THE TIME AT THE END OF EACH LOADSTEP TO 1 SECOND

CNVTOL,F,,,0                                     !DEFINE CONVERGENCE TOLERANCE FOR RESIDUAL NODE FORCES

OUTRES,ALL,ALL                           !STORE RESULTS OF STATE VARIABLES

AUTOS,OFF                                        !AUTOMATIC SUBSTEPS OFF (MIN SUBSTEP=1/DESIRED)

NROPT,FULL,,OFF

NEQIT,1000                                         !INCREASE THE MAXIMUM NUMBER OF EQUILIBRIUM EQUATIONS PER SUBSTEP FROM 15 (DEFAULT) TO 1000 TO HELP THE SOLUTION TO CONVERGE

PRED,OFF,,OFF

 

UPDATE-Adjusting the convergence tolerance values allows the solution to converge for higher displacements. But I still do not know what the numbers in the color scale mean when I use PLNSOL,PDMG,MT