** ERROR 203150 ** Failed to complete analysis within maximum number of incremental loading steps.
With the current solver parameters, the large deflection analysis could not be completed within the maximum permitted number of incremental loading steps (the default value or user-specified value).
When encountering this error, the job progress table of the large deflection analysis may display the following messages:
* CONVERGENCE FAILURE *
or
* DIVERGENCE OCCURRED *
When encountering these warning messages, look at the left column of the table, which shows the different strategies (KSTRA) used during the analysis. If the last value of KSTRA falls within the range of 0-4, the solution is considered satisfactory. However, if the last value is 5, it signifies that the structural or warpage analysis programs have reached a point where equilibrium iterations are no longer feasible, and the results obtained may be unreliable.
To assess the accuracy of the solution, a load-deflection graph can be plotted by requesting a load deflection history when reading the results. After a few steps in strategy 5, the graph typically becomes erratic, indicating an inaccurate solution. Strategy 5 is implemented because, for some non-linear problems, the program may recover after a few steps at this strategy and return to lower strategies.
When using the load control load incrementation method, the analysis cannot traverse a limit point. As the point is approached, the analysis takes smaller and smaller steps and will attempt higher non-linear strategies. Once the limit point is reached, the analysis will likely remain at its highest strategy (KSTRA=5).
Although in many cases increasing the factor controlling maximum step size can speed up the analysis, where there is a true limit point in the load path it is wise to limit the steps to about 5%, otherwise the analysis may overshoot the limit load. It is easy to spot a limit point by tracing the history of a relevant node. The slope of the load-deflection graph will approach zero at a limit point.
If such a situation (prolonged increments in strategy 5) occurs, it doesn't always indicate a limit point. It could indicate a problem with the analysis itself. To find out, follow this procedure:
Run a small deflection analysis. Check that the response is reasonable. A modeling error (or unreasonable shrinkages in the case of a warpage analysis) could cause failure of the non-linear solution.
Check the constraints in the model. In a warpage analysis, if the model is over-constrained so that the shrinkage strains are in conflict with constraints, this will often cause the large deflection analysis solution to fail, even if the small deflection result is reasonable.
Look at the load-deflection graph of some relevant nodes. If there is a true limit point or simply a very non-linear region, then the slope of the graph should gradually decrease until it is nearly horizontal. Alternatively, look at the deflected shapes of several steps just before convergence trouble occurs (this will require reading several results). A highly non-linear region in the load path (that is buckling of the plastic part) usually shows up as a significant change in shape over a small change in load.
Sometimes, if the load steps are too large, the gradual decrease in load-deflection slope is not clear (especially if a limit point was overshot). To look in more detail, re-run the analysis as follows:
i. View the analysis log and examine the Job Progress table. Note the load level (RFAC) at the step before the strategy (KSTRA) becomes 5, call this value RFAC*.
ii. Now re-run a structural or warpage analysis, but this time force the analysis to take smaller steps in the region of RFAC. For example, if trouble occurs at RFAC = 0.55, then type in a series of steps like the following as load factor increments:
0.1 , 0.1 , 0.1 , 0.1 , 0.1 .
iii. Now set the Maximum load factor increase per step to about 0.005. When the analysis takes over the load stepping (after RFAC = 0.5), all steps will be limited to a maximum of 0.005. Then repeat step 3 above, which should show the response in detail near RFAC*.
If this investigation shows that the solution failed because of a highly non-linear region in the load path, then this is strong evidence of a buckling problem with the plastic part. In fact, this is stronger evidence of a problem than any result obtained from the buckling analysis. Usually, however, the buckling analysis could be used for design purposes because it is considerably faster.