I get the following error when trying to use curve fitting to create a hyperelastic foam material model when compressive (negative values) uniaxial data was supplied to the curve fitting solver.

*** WARNING *** CP= 9.484 TIME= 13:25:08

Base term is negative in Base^Exponent. Absolute Value of Base Term is
Used

Then I get a visual C++ runtime library error and ANSYS aborts.

Is this a bug?


Yes.

In fact this was working fine in 8.0. If you have 8.0, you should be able to fit uniaxial compression data.

(-ve strains,-ve stress)

This bug was introduced in 8.1. And again fixed in 9.0


NOTE:

No defect number was ever issued - this bug was fixed without a formal record of its existence.


SAMPLE INPUT LISTING (STILL ISSUES WARNING ABOUT NEGATIVE BASE EXPONENT AND TAKE SEVERAL MINUTES TO SOLVE FOR THE COEFFICIENTS, BUT IT DOES WORK AT Release 9.0BETA UP20040819):

/batch,list
/verify,cfhy-fo22
/title,cfhy-fo22,rjayasee,Ogden Foam Model with Uniaxial Compression Data

*create,dv-378-uniaxial.exp
-0.0909091 0.027793258 -4.887613251
-0.181818 0.052677884 -8.352980402
-0.272727 0.075149245 -11.11183782
-0.315 0.085149245 -12.31183782
-0.363636 0.095590469 -13.5472426
-0.4053636 0.105590469 -14.7472426
-0.454545 0.114302669 -15.87934828
*end

/prep7

tbft,eadd,1,unia,dv-378-uniaxial.exp

tbft,fadd,1,hyper,foam,1
tbft,solve,1,hyper,foam,1,1,100
tbft,fset,1,hyper,foam,1

tblis,all,all

/delete,dv-378-uniaxial.exp





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