In springback analysis, we had no problem when gravity effect is not considered. However, after gravity effect is included in the input deck, there were some strange error messages. What might be the cause?

Double-check the density of the material model. Some people prefer to use the unit system as (gm,mm,ms), while others prefer to use (mm,s,n). If, by mistake, the incompatible unit for the density is chosen, then problem might occurs.

If larger density is chosen (for example, for mm, s, n, the density for steel is 7.8e-9. However, some people use 7.8e-3 by mistake because the later value is for the unit mm,ms,n). At this time, the whole structure of the sheet can not sustain the weight due to the wrong density, and it crashed. Accordingly, some strange error message might happen.

If smaller density is used, then the effect gravity effect might not be considered properly. If the part is big and is not very stiff, the predicted springback will be far away from experimental data.

Accordingly, Even though springback process can be regarded as a static process, we still need to be careful with material density.