PARAM, KTPLAST
Bulk Data Entry Beneficial for problems involving a combination of plasticity, contact, and pretension.
Parameter  Values  Description 

KTPLAST  <1 ≤ N ≤ 10000> No default Defaults:

PARAM,
KTPLAST, N: The elastic stiffness matrix is used for the first N nonlinear iterations, at each load step. After the first N nonlinear iterations, a consistent elastoplastic stiffness matrix is used. This allows OptiStruct to hold the element tangent stiffness matrix fixed until the contact nearly converges, and then switch to the standard elastoplastic formulation. 
Comments
 PARAM, KTPLAST, N is beneficial for problems involving a combination of plasticity, contact, and pretension.
 Currently, PARAM, KTPLAST, N is only supported for solid elements in smalldisplacement analysis.
 It should be used in conjunction with PARAM, EXPERTNL, NO.