I'm running a compression-shear analysis on a spinal fusion device and am unable to get the solution to converge long-term. What I mean by that is an individual substep will converge, then the solution loses convergence on the first iteration of the next substep. I've included an image below to show what I mean.
I've run this simulation many times using different parameters with similar results. In several cases, multiple substeps will converge, but the solution will always lose convergence in the iteration immediately following the converged iteration.
Is this a problem that can be fixed simply by adding more substeps? More generally, does this pattern (converged substep followed by immediate loss of convergence) indicate a particular solution?
I am happy to provide any further information as necessary. Thank you in advance for your help.