Implicit Nonlinear - Contact - Combination of Bolted (with preload) and Pinned Connections 1

[nmruble]

Hello,
I am relatively new to Patran so please bear with me ...
I am looking to model an assembly in Patran, somewhat like a four-bar linkage. In the rear, the top link is pinned to the back link, and the bottom link is pinned to the back link. In the front, the top link is bolted to the front link and the bottom link is bolted to front link. The surface of the rear link is constrained translationally in all directions, and a uniformly distributed load is applied to the surface of the front link (I modeled this as a pressure). The bolts and pins were also drawn as solid geometry and meshed. I defined each solid as a contact body and created a contact table to solve using sol600. Each bolt and pin is connected to a 1d bush soft spring (made using a bar connected the center node of the bolt end to a translated node normal to the bolt ends surface) which is fixed nodally. Essentially, my model is a more complicated version of the lug-pin-clevis tutorial for patran. I cannot, however, get my solution to converge. Does anyone know where I could find more tutorials on modeling contact assemblies in Patran, or where I might be going wrong? Also, could anyone point me towards advice/tutorials on modeling preload in a 3D meshed bolt? Thanks so much for any help you might be able to provide!

 

[Sam_Boch]

Hey,

First off all I suggest to do a comprehensive debugging of the model:
try to replace all bolts and pins by basic rigid bush elements connected to links by rigid MPC's (No contact)
run normal modes analysis to see if the structure is defined by the way you intended.
after that you can start replacing back to bolts and pins with contact and check all contacts defined properly, that can be done using linear (sol101) runs which use same contact algorithms such as implicit nonlinear.
hopefully these steps can help you find your convergence problems.

for preloaded bolts there's a special feature in Patran which adds preload definition to meshed bolts.

if you're an academic student I suggest using MSC learning center to get access to all relevant courses of Nastran and Patran (for your case I think NAS133 and NAS400 are required) - it cost 100$ for students per year and for me it was extremely helpful to get into Patran and Nastran.

Good luck

 

[nmruble]

Thank you Sam! I will look into the learning center. To clarify, did you mean create a node in the center of the hole for each link (make that node a bush), and use rbe2 to web from that node to the nodes that the bolt would touch, and then use a cbeam to connect the rbe2 at each end of the hole through the links. Not sure yet how to properly make rigid connections and was thinking that would be how I would go about it.