abaqus umat

a simple approach could be to define 2 umats in the same umat routine. here is how:

1. u can define material props for umat. so for elements that use umat1, provide prop=1, for umat2 prop=2

now combine umats like this:

subroutine umat

...

if (prop=1) then

call umat1(...)

elseif (prop=2) then

call umat2(...)

end

end subroutine umat

subroutine umat1

...

end subroutine umat1

subroutine umat2

...

end subroutine umat2

Since the input arguments are same for all umat routines, its not a lot of work to combine. 

this may not be very efficient, there could be better ways of doing it that i am not aware of.

Yes, the above approach is quite similar to the manual 's suggestion:

Abaqus, user subroutine reference, 1.1.31–9

~~~~~~~~~~~~~~~~~~~~~

Example: Using more than one user-defined mechanical material model
To use more than one user-defined mechanical material model, the variable CMNAME can be tested for
different material names inside user subroutine UMAT as illustrated below:

IF (CMNAME(1:4) .EQ. 'MAT1') THEN
    CALL UMAT_MAT1(argument_list)
ELSE IF(CMNAME(1:4) .EQ. 'MAT2') THEN
    CALL UMAT_MAT2(argument_list)
END IF

UMAT_MAT1 and UMAT_MAT2 are the actual user material subroutines containing the constitutive
material models for each material MAT1 and MAT2, respectively. Subroutine UMAT merely acts as a
directory here. The argument list may be the same as that used in subroutine UMAT.