Learning Forum

[boonthiam13]

Hi guys, I hope someone can help in overlooking the issue I faced. I encountered message as below after I changed some of the contacts from bonded to frictionless and the model failed to converge now:n***Element 34852 located in Body A Grider Segment\\Solid (and maybe other elements) has become highly distorted. You may select the offending object and/or geometry via RMB on this warning in the Messages window. Excessive distortion of elements is usually a symptom indicating the need for corrective action elsewhere. Try incrementing the load more slowly (increase the number of substeps or decrease the time step size). You may need to improve your mesh to obtain elements with better aspect ratios. Also consider the behavior of materials, contact pairs, and/or constraint equations. If this message appears in the first iteration of first substep, be sure to perform element shape checking. Named Selections for the offending element can be created via the Identify Element Violations property on the Solution Information Object.***nAs the message suggested, I have been refining the mesh till the limit that my personal laptop can handle and reducing the load size but still cannot get the model converge. I attached wbpz file in the link below for your reference. Would be grateful if someone could assist me to troubleshoot this model.nnhttps://drive.google.com/drive/folders/1X7b1gdWeN-InHK54k3kr-pQhJeJhVk09?usp=sharingnnThanks!nRgds,nBoo

[SaiD]

Hi Boon,nI suspect your issue is related to the contacts, since I am assuming your simulation was working when all the contacts were bonded? nTo debug, first let's look at the Newton-Raphson residuals. To do this, go to Solution Information-->Details-->Newton-Raphson Residuals --> 2 (the number indicates that last 2 Newton-Raphson residual plots will be saved). Then solve the simulation and plot the Newton-Raphson residuals. This is a useful debugging tool in general to figure out the region that is causing convergence issues.nIf the residuals are high in the contact region, then try to reduce the normal contact stiffness. To do this, select the contact pair where the residuals are high. Details of contact pair-->Advanced-->Normal Stiffness --> Manual and Normal Stiffness Factor-->0.1nnHope this helps,nSain

[wancheng gao]

Hi SaiD, May I ask a question? In my static strutural model using ANISO material, one of  the contact regions is for debonding cohesize zone model and I found out high newton raphson residuals in there. Do I also need to reduce the normal contact stiffness? I am confused that the normal contact stiffness is for closing the contact or openning the contact? If for both, that makes more sense. I also saw highly distorted element at this location. Should i refine the mesh anyway? Because I think the mesh is fine already.

Thank you for your help!