Product: ABAQUS/Standard
User subroutine UHYPER:
can be used to define the strain energy potential for isotropic hyperelastic material behavior;
is called at all material calculation points of elements for which the material definition contains user-defined hyperelastic behavior;
can include material behavior dependent on field variables or state variables; and
requires that the values of the derivatives of the strain energy density function of the hyperelastic material be defined with respect to the strain invariants.
There are several special considerations that need to be noted.
When UHYPER is used to define the material response of shell elements that calculate transverse shear energy, ABAQUS/Standard cannot calculate a default value for the transverse shear stiffness of the element. Hence, you must define the element's transverse shear stiffness. See “Shell section behavior,” Section 15.6.4, for guidelines on choosing this stiffness.
If this capability is used to describe the material of elements with hourglassing modes, you must define the hourglass stiffness for hourglass control based on the total stiffness approach. The hourglass stiffness is not required for enhanced hourglass control, but you can define a scaling factor for the stiffness associated with the drill degree of freedom (rotation about the surface normal). See “Section controls,” Section 13.1.4.
SUBROUTINE UHYPER(BI1,BI2,AJ,U,UI1,UI2,UI3,TEMP,NOEL,
1 CMNAME,INCMPFLAG,NUMSTATEV,STATEV,NUMFIELDV,FIELDV,
2 FIELDVINC,NUMPROPS,PROPS)
C
INCLUDE 'ABA_PARAM.INC'
C
CHARACTER*80 CMNAME
DIMENSION U(2),UI1(3),UI2(6),UI3(6),STATEV(*),FIELDV(*),
2 FIELDVINC(*),PROPS(*)
user coding to define U,UI1,UI2,UI3,STATEV
RETURN
ENDU(1)
, strain energy density function. For a compressible material, at least one derivative involving 
should be nonzero. For an incompressible material, all derivatives involving will be ignored. The strain invariants—
, 
, and —are defined in “Hyperelastic behavior,” Section 10.5.1.
U(2)
, the deviatoric part of the strain energy density of the primary material response. This quantity is needed only if the current material definition also includes Mullins effect (see “Mullins effect in elastomers,” Section 10.6.1).
UI1(1)
UI1(2)
UI1(3)
UI2(1)
UI2(2)
UI2(3)
UI2(4)
UI2(5)
UI2(6)
UI3(1)
UI3(2)
UI3(3)
UI3(4)
UI3(5)
UI3(6)
STATEV
Array containing the user-defined solution-dependent state variables at this point. These are supplied as values at the start of the increment or as values updated by other user subroutines (see “User subroutines: overview,” Section 25.1.1) and must be returned as values at the end of the increment.
BI1
.
BI2
.
AJ
.
TEMP
Current temperature at this point.
NOEL
Element number.
CMNAME
User-specified material name, left justified.
INCMPFLAG
Incompressibility flag defined to be 1 if the material is specified as incompressible or 0 if the material is specified as compressible.
NUMSTATEV
User-defined number of solution-dependent state variables associated with this material (see “Allocating space” in “User subroutines: overview,” Section 25.1.1).
NUMFIELDV
Number of field variables.
FIELDV
Array of interpolated values of predefined field variables at this material point at the end of the increment based on the values read in at the nodes (initial values at the beginning of the analysis and current values during the analysis).
FIELDVINC
Array of increments of predefined field variables at this material point for this increment; this includes any values updated by the user subroutine USDFLD.
NUMPROPS
Number of material properties entered for this user-defined hyperelastic material.
PROPS
Array of material properties entered for this user-defined hyperelastic material.