Linear Penalty Curve (Nonlinear Analysis)

For nonlinear analysis, the contact condition does not change within an iteration, during reevaluation at the end of each iteration, if the contact condition for some or all contact elements has changed, the revised contact condition is used for the subsequent iteration. Therefore the over the course of a nonlinear analysis the contact can open or close multiple times. The Contact stiffness is KA when closed and KB when open, similar to the linear case; however, since the contact status can change, the Contact element force is not tensile, with slope KA, when the contact moves from closed to open status. When the contact is open, the normal stiffness is essentially zero (very small slope KB to avoid singularities). The closure of the contact element increases the stiffness value to KA.

Figure 1. Penalty-based Contact Element Force-Displacement Curves for Nonlinear Analysis

The STIFF field on the PCONT Bulk Data Entry can be used to control the stiffness of the contact interface. The AUTO, SOFT, and HARD options are available for automatic predefined stiffness setting. Additionally, a positive real value can be specified to directly prescribe the contact stiffness value. If a negative real value is specified, then it scales the STIFF=AUTO value by the specified scaling factor.