$matTag

unique material object integer tag

$Fy

yield strength

$E

initial elastic tangent

$b

strain-hardening ratio (ratio between post-yield tangent and initial elastic tangent)

$R0, $cR1, $cR2

control the transition from elastic to plastic branches.

Recommended values:

$R0=between 10 and 20, $cR1=0.925, $cR2=0.15

$a1, $a2, $a3, $a4

isotropic hardening parameters: (optional, default: no isotropic hardening)

// Default values for no isotropic hardening a1 = 0.0; a2 = 1.0; a3 = 0.0; a4 = 1.0;

$a1

isotropic hardening parameter, increase of compression yield envelope as proportion of yield strength after a plastic strain of $a2*($Fy/$E).

$a2

isotropic hardening parameter (see explanation under $a1)

$a3

isotropic hardening parameter, increase of tension yield envelope as proportion of yield strength after a plastic strain of $a4*($Fy/$E)

$a4

isotropic hardening parameter (see explanation under $a3)

$sigInit

Initial Stress Value (optional, default: 0.0)

the strain is calculated from epsP=$sigInit/$E

if (sigInit!= 0.0) { double epsInit = sigInit/E; eps = trialStrain+epsInit; } else eps = trialStrain;