This paper on "An Iterative Finite Element Method for Tool Design of Stretch Formed C-17 Skin Panel" was presented at the NAFEMS World Congress on Effective Engineering Analysis - 25-28 April 1999, Newport, Rhode Island, USA.

Abstract

This paper presents a finite element based method to develop the tool contour for the stretch forming of a doubly curved C-17 panel. The analysis utilizes an iterative algorithm to compensate for springback. At each iteration. the algorithm uses the springback calculations to modify the die surface until the die contour produces post-springback that is within the tolerance. Verification of springback predictions was achieved via coupon testing. The stretch forming simulation is performed using ABAQUS finite element code which allows for the nonlinear numerical simulation of contact surfaces. A technique for adding viscous damping to stabilize the model from numerical instabilities is also presented. The results from the simulation indicate that the die generated by the iterative scheme will produce a better fitting skin after springback than current procedure.