OptiStruct Nonlinear Convergence

In this document, three examples are presented to demonstrate the convergence issues encountered in a non-linear implicit static analysis and the remedies to overcome the convergence-issues.
The results presented in this document were obtained using OptiStruct version 2022.2
Example1: Snap-fit analysis to demonstrate the correct choice of the secondary and main surfaces in a contact pair, the use of the SOFT contact penalty stiffness option in the PCONT bulk data card and the primary difference between NLPARM and NLCTRL bulk data cards.
Example2: Denting analysis to demonstrate the convergence issue encountered due to the application of a force on a rigid body and the remedies to prevent the rigid body motion like removing the initial gap between contacting surfaces, the use of contact stabilization (CNTSTB) and the use of weak grounded springs (CELAS2).
Example3: Motion between two solid deformable blocks to demonstrate the use of the CLEARANCE option in the PCONT card to prevent unconstrained rigid body motion.
A PDF file is attached with the details. In the article body here, only the animations are embedded as the animations cant be included in a PDF file.
The same title that is used in the PDF file is used here followed by the animation so that the reader can locate the animation when looking at the PDF file.

Animations: Example1: Snap Fit – Runs 1 & 2      Main and secondary switched in Snap_Fit2


Animations: Example1: Snap Fit – Runs 2 & 3            STIFF = SOFT in Snap_Fit3


Animations: Example1: Snap Fit – Runs 3 & 4            EPSU, EPSP=0.0001 in Snap_Fit4

DTRAN (BWE) used in Snap_Fit7
Animation: Example1: Snap Fit – Runs 7


Thickness Gap = 2.0mm in Dent2 & Dent2a
Secondary & Main Switched in Dent2a

Animations: Example2: Denting – Runs 2 & 2a


Animations: Example2: Denting
Runs 2, Plastic Strain


Animation: Example3
Deformable Blocks – Run 2


Animation: Pitfall of Using Clearance – Dent2, Dent5


Animation: Pitfall of Using Clearance – Dent2, Dent6