8.4.1.5. Anisotropic Hyperelasticity Material Model
You can use anisotropic hyperelasticity to model the directional differences in material behavior. This
is especially useful when modeling elastomers with reinforcements, or for biomedical materials such as
muscles or arteries. You use the format TB,AHYPER,,,,TBOPT to define the material behavior.
The TBOPT field allows you to specify the isochoric part, the material directions and the volumetric part
for the material simulation. You must define one single TB table for each option.
You can enter temperature dependent data for anisotropic hyperelastic material with the TBTEMP
command. For the first temperature curve, you issue TB, AHYPER,,,TBOPT, then input the first temper-
ature using the TBTEMP command. The subsequent TBDATA command inputs the data.
See the TB command, and Anisotropic Hyperelasticity in the Mechanical APDL Theory Reference for more
information.
The following example shows the definition of material constants for an anisotropic hyperelastic mater-
ial option:
! defininig material constants for anistoropic hyperelastic option
tb,ahyper,1,1,31,poly
! a1,a2,a3
tbdata,1,10,2,0.1
! b1,b2,b3
tbdata,4,5,1,0.1
! c2,c3,c4,c5,c6
tbdata,7,1,0.02,0.002,0.001,0.0005
! d2,d3,d4,d5,d6
tbdata,12,1,0.02,0.002,0.001,0.0005
! e2,e3,e4,e5,e6
tbdata,17,1,0.02,0.002,0.001,0.0005
! f2,f3,f4,f5,f6
tbdata,22,1,0.02,0.002,0.001,0.0005
! g2,g3,g4,g5,g6
tbdata,27,1,0.02,0.002,0.001,0.0005
!compressibility parameter d
tb,ahyper,1,1,1,pvol
tbdata,1,1e-3
!orientation vector A=A(x,y,z)
tb,ahyper,1,1,3,avec
tbdata,1,1,0,0
!orientation vector B=B(x,y,z)
tb,ahyper,1,1,3,bvec
tbdata,1,1/sqrt(2),1/sqrt(2),08.4.1.6. Creep Material Model
Creep is a rate-dependent material nonlinearity in which the material continues to deform under a
constant load. Conversely, if a displacement is imposed, the reaction force (and stresses) diminish over
time (stress relaxation; see Figure 8.10: Stress Relaxation and Creep (p. 211)(a)). The three stages of creep
are shown in Figure 8.10: Stress Relaxation and Creep (p. 211)(b). The program has the capability of
modeling the first two stages (primary and secondary). The tertiary stage is usually not analyzed since
it implies impending failure.
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