how to implement mixed elements

[meepmeep]

Hello dear all,

is someone out there who would explain to me how to implement mixed elements? I did not find an answer in the manual.
Which command do I need and where do I need to put it in the attached file?

it would be very kind to tell me if you find severe mistakes in the attached file, as I'm a newbie to feap

thank you

[JStorm]

The options for mixed and enhanced element formulations are explained on page 94-97 in the manual (FEAP86).

[meepmeep]

Thank you very much for your answer!
To be more precise: I'm trying to set up enhanced assumed strain (EAS) elements.
according to the manual I need to change the material definition to

material,1
 Solid
 Plane Strain
 elastic isotropic 3550 0.5
 ENHAnced
...

am I right?
but if I do that I get the following Error:

*ERROR* Residual norm is NaN or Inf

what am I doing wrong?

thank you

[Prof. R.L. Taylor]

Please tell  us what version of the program you are using.  You also need to check the output file "O" named file to see if there is more information.  Check that what you specified in the input file has an associated output, etc.

If you are using FEAPpv, it does not have all the options available in FEAP so will not use much of the data you give, thus producing an error.

[Prof. R.L. Taylor]

You cannot specify poisson ratio of 0.5, try 0.499 -- only FEAP has incompressible (and only in ver8.6)

[meepmeep]

Thank you very much for the answer.

I am using FEAPpv, Version 8.2
It seems to work now.

Is the Mixed-Enhanced command closer to an EAS element than the Enhanced Strain command? What is the difference? 
 
thank you

[Prof. R.L. Taylor]

MIXEd ENHAnced is: "A mixed-enhanced strain method. Part I: Geometrically linear problems",
Computers and Structures, Vol 75, 237-250, 2000.

ENHAnced is EAS

[meepmeep]

Thank you very much