| Friction has been considered to significantly affect the final shape and strain distribution of a blank in sheet metal forming processes. The final product mainly depends on effective control of friction. An accurate modeling of the friction effect is essential for finite element simulation of metal forming problems.; Objectives of this research are including: (1) derive the consistently-linearized form of contact stiffness for finite element solution, (2) develop a generalized interface law and (3) develop an effective contact search algorithm.; To start with, a generalized contact/friction formulation, that allows frictional slip motion between arbitrary curved surfaces, is derived on the basis of the perturbed Lagrangian variational method. To model the interfacial behavior, a generalized friction law has been developed by analogy to plasticity. Lastly, an effective contact search algorithm has been developed to detect the kinematic incompatibilities produced between contacting bodies.; The proposed formulation and algorithm have been implemented into the nonlinear finite element program (NFAP), and extensive numerical tests have shown the developed computer code to be very reliable and effective for practical sheet metal forming problems. In addition, it has been found that friction has a significant effect on strain distribution of material in sheet forming problems. |
