CONVERGENCE OF THE NEWTON-RAPHSON ALGORITHM IN ELASTIC PLASTIC INCREMENTAL-ANALYSIS

A spatially continuous, time discrete formulation of the loading of an elastic, perfectly plastic body governed by a von Mises yield condition is presented. It is assumed that incremental changes in strain occur along minimum work paths, which is equivalent to a backward difference implicit integration algorithm or the radial return method. This assumption permits the incremental problem to be formulated as a convex non-linear programming problem. The classical Newton-Raphson algorithm can be adopted to provide an iterative solution of the non-linear programming problem. It is shown that if an elastic or secant predictor modulus is used, the algorithm converges monotonically. However, if a tangent predictor is used, a line search algorithm must be included to ensure convergence.