Why the analysis takes multiple iterations to solve even it has bonded contact and linear in nature?
There is a list of features that trigger Newton-Raphson iterations (i.e., a nonlinear solution), but having any contact elements (even if bonded) will trigger NR iterations. (The other things that trigger NR iterations - plasticity, nonlinear springs, etc. - are usually more obvious.)
What we do in Workbench Mechanical is to use the following command to force a single iteration: neqit,1, force with this, one will see the following warning printed:
*** WARNING *** CP = 2.090 TIME= 12:09:08 Using 1 iteration per substep may result in unconverged solutions for nonlinear analysis and the program may not indicate divergence in this case. Check your results.
What this warning is saying is: if the analysis is truly linear (i.e., small deflection theory), you should have force balance; if the analysis is actually nonlinear, you won't get force balance.
Now, let us say the analysis was solved as a 'linear' analysis, but large deflection effects should have been turned on - we would not know this, either, since a 'linear' analysis does not use NR method. Hence, by specifying "neqit,1, force", we are saying that we believe that it is a linear analysis, and we are forcing that assumption on the solver. If you want to be safe, then use 1 substep (NSUBST,1,1,1), but this may require multiple equilibrium iterations. If it is linear, it should converge quickly (e.g., 2-3 iterations), and one will be ensured of numerically accurate results. If one is confident that the analysis should be run as linear, then use 1 equilibrium iteration (NSUBST,1,1,1 with NEQIT,1, FORCE) and there will not be any additional checks, but the solution will just be 1 iteration, like a linear analysis.