{"id":380791,"date":"2024-08-28T06:00:52","date_gmt":"2024-08-28T06:00:52","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/380791\/"},"modified":"2024-08-28T06:10:44","modified_gmt":"2024-08-28T06:10:44","slug":"380791","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/380791\/","title":{"rendered":"Reply To: cannot converge"},"content":{"rendered":"

<p> <\/p><p>First it helps to understand the difference between loadsteps and steps\/substeps the solver takes in each loadstep:<br><br>https:\/\/www.padtinc.com\/2011\/11\/08\/you-dont-wanna-step-to-this-breaking-down-loadsteps-and-substeps-in-ansys-mechanical\/<\/p><p>For nonlinear convergence,<\/p><p>See the below – you can search also for nonlinear convergence and quite a few posts will come up that should help.<\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Some resources that might help. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Some additional links from external sources:<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part I: Using Newton-Raphson Residual Information<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>https:\/\/www.padtinc.com\/2012\/10\/10\/overcoming-convergence-difficulties-in-ansys-workbench-mechanical-part-i-using-newton-raphson-residual-information\/<\/a><\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part II: Quick Usage of Mechanical APDL to Plot Distorted Elements<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>https:\/\/www.padtinc.com\/2012\/10\/18\/overcoming-convergence-difficulties-in-ansys-workbench-mechanical-part-ii-quick-usage-of-mechanical-apdl-to-plot-distorted-elements\/<\/a><\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Nonlinear Convergence Tips<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>https:\/\/www.ansystips.com\/2018\/06\/non-linear-convergence.html<\/a><\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>1. Align nodes between contact and target if possible in the sliding direction (<\/span><span lang=”””DE”””><span lang=”””EN-US”””>link<\/span><\/a><\/span><span lang=”””EN-US”””>)<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>2. Save Newton-Raphson Residuals & Identify Element Violation before analysis starts (<\/span><span lang=”””DE”””><span lang=”””EN-US”””>link<\/span><\/a><\/span><span lang=”””EN-US”””>)<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>3. Use MPC for bonded contacts if needed (<\/span><span lang=”””DE”””><span lang=”””EN-US”””>link<\/span><\/a><\/span><span lang=”””EN-US”””>).<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>4. Set small initial time steps. Here is my default setting for difficult problems:<\/span><\/p><p class=”””MsoNormal””” align=”””center”””><\/p><p class=”””MsoNormal”””><span lang=”””DE”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>The first step would thus be 1\/100= 0.01s with a minimum time step of 1\/1000= 0.001s. Apply this to all “Current Step Number” of interest.<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>5. Have similar size mesh at contacts. If not, Contact has finer mesh while Target is coarser.<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>6. <\/span><span lang=”””DE”””><span lang=”””EN-US”””>Slice and dice<\/span><\/a><\/span><span lang=”””EN-US”””> geometry such that the volumes adjacent to contacts can be Hexahedron elements. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>         – Starting with pretty mesh by the contacts reduces the distortion during the analysis. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>         – Hexahedron elements are less distorted when capturing curved geometries (e.g. holes). <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>7. Drop Contact Normal Stiffness Factor (i.e. FKN) to 0.01. Watch out for excessive penetration.<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>8. Use <\/span><span lang=”””DE”””><span lang=”””EN-US”””>Contact Tool <\/span><\/a><\/span><span lang=”””EN-US”””>to see if any contacts are open. <\/span><span lang=”””DE”””><span lang=”””EN-US”””>Pinball radius<\/span><\/a><\/span><span lang=”””EN-US”””> may need tweaking. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>9. Switch model to Displacement driven instead of Force driven for better stability. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>10. Avoid <\/span><span lang=”””DE”””><span lang=”””EN-US”””>over-constrained<\/span><\/a><\/span><span lang=”””EN-US”””> model whenever possible (e.g. symmetry and bonded contacts) <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>11. Move the body to be just in contact so that it doesn’t ‘fly’ a small distance before touching. <\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””> For metal plasticity:<br><br>https:\/\/www.youtube.com\/watch?app=desktop&v=OZbKnxKTd_0<br><\/span><\/p><p class=”””MsoNormal”””> <\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>All the best<\/span><\/p><p class=”””MsoNormal”””><span lang=”””EN-US”””>Erik <\/span><\/p><p> <\/p><p> <\/p><\/p>\n","protected":false},"template":"","class_list":["post-380791","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"acf":[],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies\/380791","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/reply"}],"version-history":[{"count":2,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies\/380791\/revisions"}],"predecessor-version":[{"id":380797,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies\/380791\/revisions\/380797"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=380791"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}