AN ALGORITHM FOR IMPROVED CONVERGENCE IN FORMING ANALYSIS

Implicit finite element analysis of sheet-forming operations depends o n the ability to find a converged solution, which is frequently diffic ult because of changing contact and friction conditions al arbitrarily shaped interfaces. This sensitivity is aggravated when draw-in is sig nificant, when the well angle is large, and when the contact region or character changes rapidly (during re-draw, for example). A new algori thm has been developed based on the mesh normal and using a consistent full set (N-CFS) of equations, including equilibrium and contact cond itions in the non-linear set. The ''N-CFS'' algorithm exhibits remarka ble stability and strong convergence. In fact, we have not found a wel l-posed problem, i.e. one which is physically stable within the discre te numerical framework, which exhibits numerical instability. The N-CF S algorithm is presented and several challenging example problems are solved, illustrating the robustness of the new method relative to stan dard implicit formulations. A series of smaller improvements for impli cit methods are also outlined. (C) 1997 Published by Elsevier Science Ltd.